I

WEEDS AND THEIR CONTROL

in

RICE PRODUCTION

Agriculture Handbook No. 292

Agricultural Research Service

UNITED STATES DEPARTMENT OF AGRICULTURE

in cooperation with

Arkansas Agricultural Experiment Station
WEEDS AND THEIR CONTROL

in

RICE PRODUCTION > 1

JLoy J. Smith, Jr., and W. C. Shaw

Crops Research Division" '=-'"'

Agricultural Research Service

Agriculture>landbook^o. 292

Agricultural Jlesearch Service ^ UNITED STATES DEPARTMENT OF AGRICULTURE

in cooperation with

Arkansas Agricultural Experiment Station

Washingtoiv;:!). C. Issued January 1966

For sale by the Superintendent of Documents, Government Printing Office,

Washington, T . C. 20402. Price 50 cents
PRECAUTIONS

Pesticides are poisonous to man and animals. Use them only when

needed and handle them with care. Follow the directions and heed all

precautions on the labels.

Keep pesticides in closed, well-labeled containers in a dry place.

Store them where they will not contaminate food or feed, and where

children and animals cannot reach them.

When handling a pesticide, wear clean, dry clothing.

Avoid repeated or prolonged contact of pesticide with your skin.

Wear protective clothing and equipment if specified on the container

label. Avoid prolonged inhalation of pesticide dusts or mists.

Avoid spilling pesticide concentrate on your skin, and keep it out of

your eyes, nose, and mouth. If you spill any on your skin, wash it off

immediately with soap and water. If you spill it on your clothing, launder

the clothing before wearing it again.

After handling a pesticide, do not eat, drink, or smoke until you have

washed your hands and face. Wash your hands and face and any other

exposed skin immediately after applying pesticide.

To protect water resources, fish, and wildlife, do not contaminate

lakes, streams, or ponds with pesticide. Do not clean spraying equipment

or dump excess spray material near such water.

To protect honey bees and other pollinating insects that are necessary

in the production of many crops, apply pesticide, when possible, during

hours when the insects are not visiting the plants.

Avoid drift of pesticide to nearby bee yards, crops, or livestock.

Dispose of empty pesticide containers at a sanitary land-fill dump, or

bury them at least 18 inches deep in a level, isolated place where they will

not contaminate water supplies. Wrap small containers in heavy layers of

newspapers and place them in the trash can.

{AeP«4á<!üÁl^a^

P01.L0W THC LABEL

U.S. BErAlIHfHT Of AGIItUUUIE

Mention in this handbook of commercially manufactured equipment

or the use of trade names of products does not imply endorsement by the

U.S. Department of Agriculture over similar equipment or products not

mentioned.
Contents

Page

INTRODUCTION 1

THE WEED PROBLEM 1

Effect of Weed Competition on

Growth of Rice 2

Dissemination of Weeds 3

Longevity and Dormancy of Weed Seed 3

CULTURAL METHODS OF

WEED CONTROL 4

Weed-Free Seed 4

Crop Rotations 4

Land Leveling and Levee Construction 5

Seedbed Preparation 5

Seeding 6

Water Management 6

Fertilizer Management 7

Cultivation 8

CHEMICAL METHODS OF

WEED CONTROL 8

Herbicides 9

General Precautions for

Using Herbicides 10

Principles of Controlling Weeds With

Herbicides 12

IMPACT OF NEW AND IMPROVED

METHODS OF CHEMICAL

WEED CONTROL ON

RICE PRODUCTION 30

Impact on Seeding Methods and

Water Management 31

Impact on Selection of Varieties 31

Impact on Fertilizer Management 31

Impact on Insects 31

EQUIPMENT FOR WEED CONTROL. 32

Hand Sprayers 32

Tractor Sprayers 33

Fixed-Wing Airplane Sprayers 34

Helicopter Sprayers 35

CALIBRATION OF TRACTOR AND

AERIAL SPRAYERS 35

Tractor Sprayers 35

Aerial Sprayers 36

WEEDS 36

Arrowhead 37

Barnyardgrass 33

Beakrush 39

Brachiaria 41

Bulrush 42

Burhead 43

Cattail 44

Curly Indigo 45

Ducksalad 46

Fimbristylis 47

Gooseweed 48

Knotgrass 48

Mexican-weed 49

Morningglory 49

Red Rice 50

Redstem 51

Sesbania 52

Smartweed 53

Spikerush 53

Sprangletop 55

Umbrellasedge 56

Waterhyssop 57

Waterplantain 58

Waterprimrose 58

BIBLIOGRAPHY 61

APPENDIX 64

ADDENDUM 64

m
Acknowledgments

The information in this handbook is based

largely on research by personnel of the U.S.

Department of Agriculture in cooperation with

the Arkansas Agricultural Experiment Station

at Stuttgart, Ark. The authors wish to

acknowledge the cooperation of Kenneth L.

Viste, formerly with the Crops Research Division, Agricultural Research Service, U.S. Department of Agriculture, Davis, Calif., for

providing unpublished data. The authors are

also indebted to a number of investigators

whose published research results were used.

The references that were used are listed in the

Bibliography.

Industry supplied the herbicides used in

many of the experiments. The Food Machinery

and Chemical Corp., Niagara Chemical Division, Middleport, N. Y.; Monsanto Chemical

Co., Agricultural Chemical Division, St. Louis,

Mo.; Pittsburgh Plate Glass Co., Chemical Division, Pittsburgh, Pa.; and Rohm & Haas Company, Philadelphia, Pa., also provided financial

support for some of the research conducted at

Stuttgart, Ark.

The authors express appreciation to Harold

Bessee and Charles E. Green, custom aerial

applicators from Stuttgart, Ark., who gave

valuable technical advice on fixed-wing and

helicopter sprayers, respectively.

The authors thank John B. Baker, Louisiana

State University, Baton Rouge; Harry H. Hudgins, Texas Agricultural Experiment Station,

Beaumont; Ruel P. Nester, Arkansas Agricultural Extension Service, Little Rock; and H. L.

Weir, Arkansas State Plant Board, Little Rock,

for their review and suggestions in the preparation of the manuscript.

IV
WEEDS AND THEIR CONTROL

IN RICE PRODUCTION

By ROY J. SMITH, JR., and W. C. SHAW, Crops Research Division,

Agricultural Research. Service

INTRODUCTION

Weed control is one of the most laborious

and expensive steps in rice production. In

underdeveloped countries, such as India, Indonesia, Korea, and Pakistan, weeds are removed

by hand weeding. In developed countries, such

as Australia, France, Italy, Japan and the

United States, weeds are removed primarily by

chemical-cultural weed control methods.

In 1962 herbicides were used to control

weeds on 940 thousand acres of riceland in the

United States—about 52 percent of the rice

acreage—at a cost of more than $6 million

{80)} Weeds are a problem on almost every

acre of rice grown in the United States. As

new herbicides are developed for controlling

weeds in rice, herbicides will be used more

extensively. The development, acceptance, and

use of cultural, chemical, and combination

methods of weed control in rice have been outstanding.

Cultural methods of controlling weeds in rice

are an integral part of rice production. These

methods include seeding weed-free crop seed,

practicing crop rotations, leveling land.

thoroughly preparing seedbeds before seeding

the crop, selecting seeding methods that reduce

weed problems, and managing water and fertilizer properly. Where cultural methods do not

control weeds effectively, herbicides can be used

advantageously. However, combinations of cultural and chemical practices are more effective

in controlling weeds in rice than either practice

used alone. The interdependence and the interrelations of cultural and chemical methods of

weed control in rice production are emphasized

in this handbook.

This handbook is designed as a guide on weed

control in rice for research scientists, extension

specialists, county agents, vocational agriculture teachers, and organizations concerned with

rice production research and education in the

United States and abroad.

Since the status of chemical weed control in

rice is changing rapidly, and new herbicides or

new uses for older ones are being recommended, it is important to keep in touch with

the U.S. Department of Agriculture, State agricultural experiment stations, or manufacturers

of specific products for up-to-date information.

THE WEED PROBLEM

Conditions favorable for growing rice are

also favorable for the growth and reproduction

of terrestrial, aquatic, and semiaquatic weeds.

Weeds in rice produce an abundance of viable

seeds, and once these seeds infest the soil they

are difficult to remove. The practice of seeding

' Italic numbers in parentheses refer to literature

included in Bibliography, p. 61.

rice by broadcasting or drilling prevents cultivation after emergence to remove weeds. The

best approach to weed control in rice is to

prevent weed infestations by seeding weed-tree

rice and removing scattered weed seedlings

from the field before they produce seed. Atter

the soil becomes infested with weeds, however,

they may be effectively controlled by a combination of selected cultural and chemical

methods.
AGR. HANDB. 292, U.S. DEFT. OF AGRICULTURE

Effect of Weed Competition on

Growth of Rice

Weeds compete with rice for light, nutrients,

water, and other growth requirements. They

reduce yields, lower the market value of the

crop by reducing quality, and increase the cost

of harvesting, drying, and cleaning.

Both research and grower experience indicate that weeds reduce the average yield of rice

m the United States about 13 percent. Weeds

also cause losses of about 4 percent in the

quality of the harvested crop and losses of

about 3 percent due to extra land preparation,

water, and fertilizer. Thus, losses in the rice

crop due to weed competition amount to about

20 percent of the potential farm value of the

rice crop, or more than $60 million each year.

In addition, farmers spend about 9 percent of

the value of the rice crop to control weeds by

cultural, mechanical, and chemical methods, or

almost $24 million each year. Therefore, annual losses caused by weeds in the rice crop in

the United States and the cost of their control

amount to approximately $84 million.

Barnyardgrass - is a serious problem in all

ricegrowing areas of the United States. In one

field investigation at Stuttgart, Ark., plots with

one barnyardgrass plant per square foot and

with an optimum stand of rice yielded 4,380

pounds per acre of rough rice compared with

5,350 pounds from grass-free plots. Plots with

five barnyardgrass plants per square foot

yielded 3,440 pounds per acre. Thus, barnyardgrass at stands of one and five plants per

square foot reduced rice yields 18 and 36 percent, respectively.

In another field experiment at Stuttgart,

Ark., barnyardgrass was allowed to compete

with rice for 9 days after its emergence, then

was removed by handweeding and kept out

thereafter. The grass was removed when it had

one to three leaves. Plots of rough rice yielded

4,610 pounds per acre. When barnyardgrass

competed with rice for 16 and 23 days (an

additional 1 or 2 weeks), plots yielded only

3,830 and 3,810 pounds, respectively—a 17-

percent reduction as compared with competition for 9 days.

Extensive cooperative investigations by the

chemical industry and ricegrowers showed that

in Arkansas weeds reduced rice yields approximately 74 percent; in Louisiana, 35 percent; in

Mississippi, 64 percent; in Texas, 48 percent;

and in California, 36 percent (15). The most

destructive weed in these investigations was

barnyardgrass, although other grass weeds,

sedges, broadleaf weeds, and aquatic species

caused some losses.

In a 5-year field investigation at Stuttgart,

Ark., losses were greater when ducksalad, a

destructive aquatic weed, competed with rice

for an 8-week period than when it competed

for 2 or 4 weeks or all season (table 1). The

value of these losses from weed competition

ranged from $13 to $72 per acre.

TABLE 1.—Effect of ducksalad competition on

rice, Stuttgart, Ark., 1957-61

Time of

Rough rice, per acre

competition

after emergence

Yield Loss in yield

Loss in

value'

0 (check).

Pounds

5,220

4,960

4,460

3,780

4,100

Pounds Percent Dollars

2 weeks .. . 260

760

1,440

1,120

5

14

28

21

13

4 weeks . . 88

8 weeks

All season

72

56

- Scientific names of weeds are given in the section

on weeds, p. 36.

' Rough rice valued at $5 per hundredweight.

Sesbania and curly indigo lower the quality

of rice and are noxious weeds in seed rice. In

Arkansas no sesbania or curly indigo seeds are

allowed in foundation and registered seed, and

only one seed in 2 pounds of seed rice is permitted in blue tag certified seed (7). The

quality and value of milled rice is reduced by

the presence of either of these species of weeds.

A 2-year field investigation showed that

yields of rice decreased as the time sesbania

competed with rice after weed emergence increased (table 2). Another field investigation

showed that as the number of sesbania plants

per acre increased, yields of rice decreased

(table 3).

Weeds, such as sesbania, curly indigo, Mexican-weed, and red rice, reduce the value of rice

by lowering the quality of the crop. All are

difficult to remove from the rice grain. Red

rice, for example, differs from white rice by

having a red seedcoat instead of the usual

brown one. It belongs to the same species as

white rice, but in most markets milled white

rice is preferred by consumers. Rough rice

containing red grains must be milled closely

to remove the red seedcoats. Close milling

breaks many white rice kernels. Broken rice

has less value than whole milled rice. If the red
WEEDS AND THEIR CONTROL IN RICE PRODUCTION 3

seedcoat is not removed, however, the milled

rice is unattractive and its market value is

reduced.

TABLE 2.—Effect of sesbania competition on

rice, Stuttgart, Ark., 1961-62

Rough rice, per acre

Time of

competition'

Yield Loss in yield

Loss in

value0 (check)

Pounds

5,710

5,620

5,470

5,200

4,630

Pounds Percent Dollars

4 weeks . 90

240

510

1,080

2

4

9

19

4 50

8 weeks

12 weeks

15 weeks'

12.00

25.50

54.00

' Sesbania population was one-half plant per square foot.

^ Rough rice valued at $5 per hundredweight.

' Sesbania competed until rice was mature.

TABLE 3.—Effect of sesbania competition on

rice, Stuttgart, Ark., 1960-62

Sesbania plants

Rough rice, per acre

per acre

(number) 1

Yield Loss in yield

Loss in

value^

None (check) __

Pounds

5,520

5,060

4,770

4,060

3,370

Pounds Percent Dollars

5,445 460

750

1,460

2,150

8

14

26

39

23.00

10,890 37.50

21,780 73.00

43,560. 107.50

' Sesbania competed until rice was mature.

' Rough rice valued at $5 per hundredweight.

Dissemination of Weeds

Weeds are disseminated in ricefields by seeding rice that contains weed seed and by transporting weed seeds in irrigation water, on farm

machinery, and by birds and animals.

Many weeds are spread almost entirely by

seeding rice containing weed seed. Red rice,

sesbania, curly indigo, and Mexican-weed are

major weeds disseminated with seed rice.

Even cleaned seed rice may contain these weed

seeds, because they are difficult to separate

from the crop seed with available cleaning

equipment.

Many weed seeds are very light and are carried by irrigation water. These include seeds

of barnyardgrass, curly indigo, ducksalad, and

redstem. When these weeds grow to maturity

on canal banks and in ricefields, their seeds

drop into the water and are disseminated with

moving irrigation water.

Machinery used in rice production—for

breaking the land and for harvesting—carries

weed seed from field to field. Dissemination of

weed seed by machinery may be reduced by

cleaning the equipment thoroughly between use

on each field. Weeds should be controlled in

service areas where equipment is cleaned or

stored, to prevent weed seed from being carried

by equipment into ricefields. Mowing, burning,

oiling, grazing, and soil sterilants control weeds

in these areas.

Weed seeds are carried by birds, livestock,

and wild animals. Some species of blackbirds

feed largely on wild grasses, which include

paspalums (Paspalum spp.), barnyardgrass,

crabgrass (Digitaria spp.), brachiaria, and

foxtail {Setaria spp.). The diet of many species

of blackbirds contains as much as 10 percent

of barnyardgrass seed. Livestock that graze

stubble ricefields scatter weed seed either on

their hoofs or hide, or through manure. The

practice of livestock grazing pastures infested

with weeds contributes to the dissemination of

weed seed.

Longevity and Dormancy of Weed Seed

Weed seeds remain viable in the soil for

many years. In experiments initiated in 1879

in Michigan, freshly gathered seeds of 20 species of weeds were mixed with sand, placed in

pint bottles, and buried 18 inches below the

ground surface {11, 73). After 40 years'

burial, viable seeds were present in 12 species

of weeds; after 80 years' burial, viable seeds

were present in 3 species of weeds—common

eveningprimrose {Oenothera biennis L.), curly

dock {Rumex crispus L.), and moth mullein

{Verbascum blattaria L.).

Although weed seeds are viable, they may be

incapable of germination immediately after

maturity, even when conditions are favorable.

This characteristic is called dormancy. Seeds

of cocklebur {Xanthium spp.), wild oat {Avena

fatua L.), and redroot pigweed {AmarantMs

retroflexus L.) exhibit dormancy {73). Seeds

of barnyardgrass may lie dormant in the soil

for 10 to 48 months after maturity before they

will germinate {3, J^). Secondary dormancy

may occur after a period in which the seeds can

germinate. For example, seeds of barnyardgrass were dormant for 10 months immediately

after they matured on the plant. They then

went through a period in which they germi-
AGR. HANDB. 292, U.S. DEPT. OF AGRICULTURE

nated. After submergence for 4 or 5 months,

these seeds went through a period of secondary

dormancy in which they did not germinate.

Environmental factors, such as variations in

drying and wetting and changes in temperatures, help to break primary and secondary

dormancy of barnyardgrass seeds.

Experiments, therefore, indicate that once

weed seeds are present in the soil they infest

ricefields for many years.

CULTURAL METHODS OF WEED CONTROL

Cultural practices of weed control are those

that (1) prevent or reduce weed infestations,

(2) suppress weed growth, and (3) kill weeds.

Cultural methods of controlling grass and

broadleaf weeds in rice predominate in the

United States. Weed-free seed, crop rotations,

land leveling and levee construction, seedbed

preparation, seeding methods, and water and

fertilizer management are all vital in a weedcontrol program. The use of herbicides in combination with effective cultural practices is

more effective in controlling weeds in rice than

either cultural or chemical methods used alone.

Weed-Free Seed

Planting weed-infested crop seed is one of

the major ways of infesting clean fields with

weeds. Red rice, a serious weed in ricefields, is

spread largely by planting rice seed containing

seeds of red rice. Other weeds, such as sesbania, curly indigo, barnyardgrass, Mexicanweed, and beakrush, are also spread when

planting rice seed. Once weeds infest a ricefield, they are difficult to control.

The ricegrowing States have regulations on

the sale and distribution of certified or registered seed that contain noxious weed seeds.

Seed-certification programs provide for inspecting seed fields and harvested seed for the presence of weed seeds as well as for other aspects

of seed quality. The seeding of rice seed grown

under certification standards is a sound practice of weed control.

The use of herbicides to control weeds in the

rice crop helps in the production of weed-free

seed. The use of propanil to control barnyardgrass, brachiaria, and other annual grasses and

the use of phenoxy herbicides to control curly

indigo, sesbania, Mexican-weed, umbrellasedge,

spikerushes, beakrush, and other broadleaf

and sedge weeds can reduce weed-seed infestations in rice seed.

Crop Rotations

Properly managed rotations combined with

use of herbicides are important for controlling

weeds in rice. Weed competition in rice is

effectively reduced in Louisiana and Texas by

a rice-pasture rotation, and in Arkansas by a

rice-soybean-oat rotation. To obtain maximum

benefits during the year rice is grown, all crops

in the rotation must be kept weed free.

In Louisiana and Texas a rice-pasture rotation reduces infestations of red rice, sesbania,

curly indigo, Mexican-weed, cattails, bulrush,

and many species of annual sedges. If sesbania,

curly indigo, Mexican-weed, or annual sedges

infest the pasture crop they should be controlled by timely applications of phenoxy herbicides. Although the rice-pasture rotation controls many species of weeds, it does not control

barnyardgrass satisfactorily.

In Arkansas, rice-soybean-oat or rice-soybean rotations significantly reduce infestations of barnyardgrass, sesbania, curly indigo,

ducksalad, spikerushes, umbrellasedges, and

other weeds. The soybean crop in a rice-soybean-oat rotation can be kept weed free by

combining cultural practices with use of preemergence herbicides. The oat crop can be kept

free of bi'oadleaf weeds by the use of 2,4-D or

MCPA. The land may also be summer-fallowed

after oat harvest to control weeds not controlled in the soybeans and oats. Summer

fallow is especially effective in controlling barnyardgrass.

Crop rotation experiments at Stuttgart, Ark.,

from 1931 thi'ongh 1940 showed that rice and

cultivated soybeans planted in alternate years

significantly reduced grass, broadleaf, and

sedge weeds in the rice crop when compared

with rice cropped continuously (6^). Barnyardgrass was one of the main weeds in this experiment. Furthermore, barnyardgrass and other

weeds were most effectively controlled with a

crop rotation consisting of 1 year of rice followed by 2 years of cultivated soybeans.

Crop rotations coupled with hand pulling of

scattered plants are important in controlling

red rice. Pasture; cultivated row crops, such

as soybeans, grain sorghums, and cotton; and

summer and fall fallowing after harvest of a

small grain crop are rotation practices that reduce problems with red rice in the rice crop.

Rotations of rice with an unirrigated row

crop, such as saffiower, or with fallow are

valuable in California for reducing populations

of cattails, bulrush, spikerush, and other perennial weeds with large rootstocks. For fallow to
WEEDS AND THEIR CONTROL IN RICE PRODUCTION

successfully control these weeds, the soil must

be dried to a depth of 12 inches.

The combination of crop rotations and use

of herbicides is more effective in controlling

weeds in rice than either practice used alone.

Preemergence and postemergence herbicides

applied on row and pasture crops rotated with

rice also reduce weed populations in the rice

crop. Likewise, propanil and phenoxy herbicides used to control grass, broadleaf, and sedge

weeds in the rice crop reduce weed infestation

in the crops rotated with rice as well as in the

rice crop.

Land Leveling and Levee Construction

Land leveling, combined with construction of

levees to permit uniform depth of irrigation, is

important in a weed-control program. Land

leveling permits maintenance of a uniform

depth of water on the field and allows adequate

surface drainage. Land used for rice should be

devoid of hummocks, ridges, sloughs, and hollows.

Aquatic weeds, including umbrellasedge,

spikerush, ducksalad, algae, gooseweed, cattails,

and bulrush, are most numerous in low areas

where surface drainage is inadequate. Other

weeds, including barnyardgrass, sesbania, and

curly indigo, may be a problem on the ridges

where water does not cover the land adequately.

Therefore, land leveling and levee construction

to eliminate low and high areas in the ricefield

and to maintain 4 to 8 inches of water on the

ricefield reduce problems with weeds. In addition, leveled land requires fewer levees; this

facilitates control of grass and broadleaf weeds

on the levees, which are ideal places for growth

and reproduction of weeds. Elimination of

levees reduces reinfestation areas for weeds.

Research in Arkansas and California has

shown that plastic levees may be used satisfactorily in ricefields to control water (38, 57).

Plastic levees help control grass and broadleaf

weeds because they eliminate the need of soil

levees where weeds grow and produce seed that

fall onto the soil or water and reinfest the ricefield. Barnyardgrass, brachiaria, sesbania, curley indigo, morningglory, and smartweed are

serious problems on soil levees. But methods

have not yet been developed for adopting plastic levees to general field usage.

Herbicides reduce problems with weeds on

ricefields with improper land leveling. Silvex,

2,4-D, 2,4,5-T, and MCPA control weeds, such

as umbrellasedge, spikerush, ducksalad, gooseweed, and bulrush, that are associated with low

or wet areas in the ricefield. Likewise, propanil

reduces barnyardgrass infestations, and 2,4-D,

2,4,5-T, and silvex control sesbania and curly

indigo infestations that are associated with

high areas in the ricefield where 4 to 8 inches

of water cannot be maintained. Weed infestations of barnyardgrass, sesbania, curly indigo,

and smartweed on levees are reduced by herbicides, such as propanil, 2,4-D, 2,4,5-T, MCPA,

and silvex.

Seedbed Preparation

One of the primary aims of seedbed preparation is to eliminate weeds. The seedbed may be

prepared in many ways—plowing, disking, harrowing, rotary tilling, and combination methods. The best method to use depends on the

soil, rotation, previous crop, seeding method,

and perhaps other conditions. Regardless of

the method used, the seedbed should be prepared to eliminate all weed growth at the time

of seeding rice. When a rotation includes a

spring-harvested crop, the land may be prepared during the summer and fall by repeated

and timely cultivations or diskings to rid the

field of many weeds. Then just before seeding

rice in the spring the soil should be disked or

harrowed to eliminate all weeds.

Thorough seedbed preparation helps to control all weeds that infest ricefields. By killing

the weeds when preparing the seedbed, the

weeds must germinate from seed or must

emerge from root or stem parts after the rice

is seeded. They are young and in the seedling

stages during the early part of the rice-growing

season. Herbicides may be used more effectively on young weed plants than on older

established ones. Thorough seedbed preparation to rid the field of all weeds just before

seeding the rice crop increases the effectiveness

of herbicides used after the rice crop germinates and emerges.

Repeated cultivations in the spring at 1- to

3-week intervals before seeding rice reduces

barnyardgrass and other annual grass infestations. The last cultivation should be shallowusually not more than 2 or 3 inches—so that

viable seed will not be brought near the surface

of the soil. This method is not effective on

aquatic species, such as ducksalad, redstem,

spikerush, umbrellasedge, and algae. Seeding

rice on a roughly prepared seedbed, especially

on heavy clay soils, discourages germination ot

barnyardgrass, umbrellasedge, spikerush, redstem, waterplantain, burhead, and seedling cattail. In California, thorough plowing ioUowea

by complete drying of soil before seeding rice

in water controls established plants of cattail,

spikerush, and knotgrass. This method is ineffective in the southern rice-producing areas

because spring rains prevent sufficient drying

of the soil to kill the weeds.
AGR. HANDB. 292, U.S. DEPT. OF AGRICULTURE

Seeding

Rice may be drill seeded, sown broadcast on

dry soil and disked or harrowed to cover, or

sown in water by aircraft. Barnyardgrass is

difficult to control by cultural or mechanical

methods on drill-seeded or dry-broadcast-seeded

rice. Seeding rice in water, therefore, was

started in California to control barnyardgrass

(1). This method reduces most infestations of

barnyardgrass by inhibiting germination and

growth. Investigations at Biggs, Calif., in

which pot culture methods were used, indicated

that common varieties of barnyardgrass seeded

on puddled soil emerged to a 100-percent stand

and those submerged 2, 4, 6, 8, or 10 inches

emerged to a 10-, 5-, 1-, 0-, and 0-percent

stand, respectively (48). Submergence not only

reduced barnyardgrass infestations but it also

delayed germination and emergence. However,

some varieties of barnyardgrass germinate in

submerged soil. In the pot-culture experiments

at Biggs, Calif., white barnyardgrass emerged

when submerged to a depth of 10 inches, although flooding did delay emergence (48).

Propanil effectively controls barnyardgrass

in ricefields where deep water cannot be maintained. Propanil also controls white barnyardgrass, which is not controlled by deep water.

In a field experiment in California in 1956

(33), rice yielded 5,500 pounds per acre; and

weeds, such as barnyardgrass and spikerush,

were controlled where water was held all season

at a depth of 6 inches. Where the water was

lowered from 6 inches to 2 or 3 inches at 2, 3,

and 4 weeks after seeding, rice yielded 3,500,

2,900, and 3,800 pounds per acre, respectively.

Where the water was lowered at 2 weeks, barnyardgrass infested the plots. When the water

was lowered at 3 or 4 weeks, barnyardgrass was

controlled but spikerush infested the plots and

reduced the yield of rice. Where deep water

cannot be maintained on the rice for extended

periods, herbicides can be used to control

weeds. If barnyardgrass infestations develop

after water has been lowered or drained

from ricefields, they can be controlled with

propanil. If spikerush infestations develop,

they can be controlled with 2,4-D, 2,4,5-T, or

MCPA.

Because rice usually germinates and grows

well under 4 to 8 inches of water, water seeding may be used to selectively control barnyardgrass, brachiaria, sesbania, curly indigo, and

sprangletop, provided the water can be held on

the rice for 3 to 4 weeks after seeding. Sometimes, however, the water level must be lowered

because the water stretches and weakens the

rice plant. Lowering or draining the water

allows germination of many weeds, such as

barnyardgrass, curly indigo, sesbania, sprangletop, and spikerush. Conversely, water mamtained on the ricefield for several weeks after

seeding intensifies problems with certain aquatic weeds, such as ducksalad, waterhyssop, and

algae. Barnyardgrass can be controlled with

propanil. Ducksalad and waterhyssop can be

controlled with 2,4-D or MCPA. Herbicides,

therefore, are essential to effectively control

weeds that may develop under any seeding

method.

In California, water seeding is practiced on

about 95 percent of the rice acreage to control

barnyardgrass, spikerush, and sprangletop. In

Southern ricegrowing areas, water seeding is

practiced on about 25 percent of the acreage to

control barnyardgrass. In California, if late

spring rains germinate barnyardgrass seed before rice is planted, the field must be cultivated

to kill barnyardgrass seedlings. The soil should

then be thoroughly dried before flooding and

seeding to prevent algae from infesting the

field.

Water Management

Flooding rice to a depth of 4 to 8 inches

when it is in the seedling stage reduces infestation of barnyardgrass. The barnyardgrass

should be in the 1- to 3-leaf stage, and water

should remain on the field 1 to 3 weeks to kill it.

High water temperatures (95° F. or above)

facilitate control of barnyardgrass, presumably

because of the low oxygen content of warm

water. Rice may be stretched and weakened by

4 to 8 inches of water. Water temperatures of

95° or above may also injure the rice. When

only hard water—such as water pumped from

shallow wells in certain areas of Arkansas—

is available, young rice may be injured severely

by deep and prolonged flooding even where

water temperatures are optimum. Early flooding to control grass weeds, therefore, has a

narrow margin of selectivity and must be used

with caution. Herbicides used in combination

with water management practices control weeds

more effectively than either practice alone.

Timely and thorough draining of the water

from the ricefield helps control many aquatic

weeds, including algae and ducksalad. Experiments in Arkansas showed that algae, or

"scum," may be controlled by lowering or

draining water from the field as soon as green

areas of algal growth appear on the soil (69).

Water may be manipulated on and off the field

to keep algal growth at a minimum until the

rice plants are large enough (12 to 18 inches

tall) to be unaffected by the algae.

Young ducksalad and other aquatic weeds

(either emersed or submerged) are effectively
WEEDS AND THEIR CONTROL IN RICE PRODUCTION

controlled by draining the flood water from the

field. The soil must become thoroughly dry to

control these weeds, but rice will also be injured if the soil becomes "sunbaked."

When draining a ricefield, care must be

exercised to prevent germination, emergence,

and infestations of barnyardgrass. Early in

the season, or during the algal-growth period,

water left off the field for more than 3 or 4

days allows grass weeds, particularly barnyardgrass, to infest the ricefield. The water, therefore, must be manipulated to control algae, to

prevent desiccation of rice, and to forestall

germination or emergence of barnyardgrass.

Accomplishing all these is difficult in commercial ricefields.

Herbicides may be combined advantageously

with water management practices. Combination treatments with herbicides, such as propanil and 2,4-D, are changing water management

practices in rice production in the West and in

the South. A water depth of 6 inches or more

is used primarily to control barnyardgrass in

California (105). The use of propanil and other

herbicides, such as 2,4-D and MCPA, to control

weeds is having a revolutionary impact on rice

culture, including seedbed preparation, levee

construction, timing and methods of seeding,

fertilizer practices, and water management.

Chemical weed control thus offers unusual opportunity for water conservation and lowering

the cost of rice production.

Fertilizer Management

Phosphate and nitrogen applied directly to

rice stimulate growth of many weeds, including

barnyardgrass, ducksalad, and algae, but

potash applied directly to rice apparently has

little or no effect on the growth of weeds.

Phosphate

Time and method of applying phosphate are

very important when barnyardgrass and other

grass-weed seeds infest ricefields in southern

ricegrowing areas. Phosphate applied before

dry seeding rice stimulates growth of young

plants of barnyardgrass. Where fields have a

history of severe infestation of barnyardgrass,

phosphate should be applied to a crop in the

rotation other than rice or treatment should

be delayed until just before the rice is inundated the first time. Broadcasting phosphate

on the soil surface combined with incorporating

it in the top 2 or 3 inches of soil stimulates

growth of grass weeds. When applications of

phosphate are required before planting rice, it

should be applied several inches below the rice

seed while drilling. It should not be applied

broadcast before seeding rice in dry soil but it

may be applied just before the first watering

without stimulating grass weeds on ricefields

not infested with barnyardgrass. Phosphate

should not be applied to standing water because

it stimulates algae or other aquatic weeds or

may be used ineffectively by the rice.

In California, phosphate is applied to thoroughly dry soil, the field is flooded, and then the

rice is seeded. Phosphate applied before seeding enables the rice plants to grow rapidly and

to compete better with grass weeds. Herbicides, such as propanil and MCPA, can reduce

weed infestations on ricefields where phosphate

has stimulated weed growth.

The soil in many ricefields in the South is low

in available phosphate (12, 109). These soils

require supplemental applications of phosphate

fertilizers for rice production. Phosphate requirements of annual plants are relatively

heavy during the first few weeks after germination {61). In southern rice-producing areas,

phosphate is applied to crops in the rotation

and not to the rice to reduce grass-weed infestations. Conceivably, this practice could result in a phosphate deficiency during the early

stages of rice development when phosphate is

needed most by the rice plant. The use of herbicides to control grass weeds will require a

re-evaluation of phosphate requirements and of

application practices in rice production. Perhaps where herbicides are used to control grass

weeds, the rice plants can use phosphate more

efficiently if it is applied before planting rather

than at other times.

Nitrogen

Time of applying nitrogen to rice is important in preventing losses in rice yield due

to barnyardgrass competition. In Arkansas,

nitrogen applied to dry-planted rice before

seeding stimulates growth of barnyardgrass.

When rice was heavily infested with barnyardgrass, application of nitrogen at the heading

stage of barnyardgrass reduced competition.

Application of nitrogen at the vegetative stage

of the grass enhanced competition of grass with

rice (table 4).

The 1963 nitrogen recommendations for rice

production by the Arkansas Agricultural Extension Service were different where grass

weeds were absent or controlled than where

they were present. For example, on a midseason variety, such as Bluebonnet 50, where

65 pounds or more per acre of nitrogen was

required, the recommendations were:

(1) Where grass is a problem, apply one-half of the

nitrog-en after grass begins heading, or about 50 days

but not later than 60 days after rice emergence, and
8 AGR. HANDB. 292, U.S. DEPT. OF AGRICULTURE

apply one-half 10 days later. (2) Where grass is not a

problem or is controlled with herbicides, apply one-half

of the nitrogen 15 days after rice emergence or before

the first flooding and one-half 65 days after rice emergence.

Under California conditions, however, delayed nitrogen fertilization does not aid in controlling weeds.

TABLE 4.—Effect of time and rate of application of nitrogen on yield of rice heavily

infested ivith barnyardgrass, Stuttgart,

Ark., 1957 and 1959

Stage of barnyard- Rate of

nitrogen

per acre

Yield of rice per acre

grass when nitrogen

was applied' 1957 1959 Average

Untreated check

Heading

Mature

Vegetative and heading'^

Vegetative and mature^ _ Heading and mature-__.

Pounds

None

( 60

<120

Uso

60

120

120

120

Pounds

2,090

2,900

3,270

3,470

2,390

2,360

2,500

3,070

Pounds

1,900

1,780

2,730

3,380

1,840

1,370

1,530

2,470

Pounds

1,990

2,340

3,000

3,430

2,120

1,860

2,010

2,770

L.S.D. at 5-percent

level 900

1,200

720

950

810

L.S.D. at 1-percent

level 1,080

' Vegetative, heading, and mature stages were 3, 8, and

12 weeks after emergence of rice and barnyardgrass.

- 60 pounds per acre applied at each stage.

In California and in southern ricegrowing

areas where rice is water seeded, nitrogen may

be applied before seeding. In southern ricegrowing areas, this treatment stimulates

growth of aquatic weeds, such as ducksalad,

waterhyssop, algae, spikerush, and umbrellasedge. Nitrogen applied to standing water

stimulates the growth of weeds and reduces efficient utilization of nitrogen by rice. If nitrogen

stimulates excessive weed growth, herbicides,

such as propanil, 2,4-D, MCPA, 2,4,5-T, and

silvex, can be used to reduce weed infestations.

Herbicides, such as propanil, 2,4-D, and

2,4,5-T, reduce problems with barnyardgrass

and broadleaf and sedge weeds by reducing

weed competition in rice. Where herbicides are

used, nitrogen applications can be managed

efficiently and the rice plant can use nitrogen

effectively.

Cultivation

Weed control in Asia, including such countries as India, Indonesia, Korea, the Philippine

Islands, Taiwan, and Thailand, consists mainly

of hand weeding. The rice is transplanted in

rows to facilitate hand-weeding practices. The

weeds are pulled by hand and piled on the

levees or buried with the hands and feet in the

soft, muddy soil. Sometimes hand tools, such

as knives, hoes, and machetes, are used to

destroy the weed growi;h. In Japan, weeds are

controlled by mechanical methods as well as by

hand weeding. Rotary and basket-shaped weeders driven by hand, animal, or power are directed between the rows to cut, bury, and kill

weeds.

In the United States, cultivation methods

other than rotary hoeing to remove weeds after

the crop is seeded are just about nonexistent

in rice culture. In drill-seeded rice, "weeding"

or cultivation between rows to remove weeds

is limited; and if rice is dry broadcast or water

seeded, cultivation to control weeds is not possible.

Dry-seeded rice may be cultivated with a

rotary hoe in some production areas. It must

be cultivated soon after emergence and while

the weeds are very small. The soil must contain the right amount of moisture; it must be

neither too dry nor too wet. Rotary hoeing

seldom controls weeds because timing and soil

conditions are so critical.

CHEMICAL METHODS OF WEED CONTROL

Chemical control of broadleaf weeds in rice

began with the use of 2,4-D. In 1963 more

than half of the rice crop was sprayed to control broadleaf weeds.

CIPC was used in 1960 and 1961 in Arkansas

to control grass weeds in rice. It was used on

only a small acreage because of the critical requirements for effective weed control without

crop injury. It had to be applied when grass

weeds were in the 1- to 2-leaf stages of development, on rice seeded 1 to 2 inches deep in the

soil, and when moisture was adequate to activate the herbicide.

The first experiments in Arkansas with propanil in 1959 showed that it effectively controlled certain young grass and broadleaf weeds

in rice. Propanil was very selective, and early

postemergence treatments at high rates (8 to

10 pounds per acre) did not injure rice. Rice

farmers in cooperative trials with commercial

chemical companies used propanil in commercial fields in 1961 on about 20,000 acres (Í5).
WEEDS AND THEIR CONTROL IN RICE PRODUCTION

In 1962 propanil was recommended by the

Agricultural Experiment Stations in Arkansas,

Mississippi, and Texas, and farmers treated

approximately 250,000 acres. Good to excellent

grass and weed control and significant improvement in yields were obtained on more than 90

percent of the fields treated (16). In 1963 and

1964 propanil was used by rice fai'mers on

more than 50 percent of the rice acreage.

Herbicides

Many herbicides are used to control weeds in

rice, and many others are being evaluated experimentally to determine their usefulness.

Only those of current general interest and usefulness are described in this handbook.

Phenoxy Herbicides

Phenoxy herbicides, such as 2,4-D, MCPA,

2,4,5-T, and silvex, are used as postemergence

selective herbicides to control broadleaf weeds

in rice.

Phenoxy herbicides usually are formulated

and marketed as two basic types—salts and

esters. They are low to intermediate in oral

toxicity (LD-,„ = 375 to 1,200 milligrams per

kilogram)."

The most widely used salts of 2,4-D, MCPA,

and 2,4,5-T include such amines as diethanolamine, triethanolamine, alkanolamine, dimethylamine, triethylamine, and isopropylamine.

These amine salt formulations are available

chiefly as water soluble liquids and are practically nonvolatile, which makes them much

safer than ester formulations to use near

valuable susceptible plants.

Esters of the phenoxy herbicides are high or

low volatile. The high-volatile esters include

methyl, ethyl, isopropyl, butyl, and amyl. The

low-volatile esters include the butoxyethanol, butoxyethoxypropanol, capryl, ethoxyethoxypropanol, isooctyl, and propylene glycol butvl ether.

These esters of 2,4-D, MCPA, 2,4,.5-T, and silvex are liquids which, when properly formulated, form oil-in-water emulsions. In areas

near susceptible crops, low-volatile esters are

less hazardous than high-volatile ones when

temperatures are 95'^ F. or less. When temperatures exceed 95°, the vapors of even the lowvolatile esters may injure susceptible crops.

Ricegrowing States have laws prohibiting the

use of high-volatile esters, but low-volatile es-

^ ^ The symbol LD50 means the lethal dosage that kills

oO percent of the experimental animals; the dosage is

expressed as milligrams of substance per kilogram of

body weight.

ters of 2,4-D, MCPA, 2,4,5-T, and silvex may

be used to control broadleaf weeds in rice.

Carbamates

Although CIPC has had limited usefulness

for weed control in rice, it is the only carbamate cleared for such use. However, the carbamates include several newer herbicides, such as

swep and molinate (discussed under New

Herbicides), which show considerable promise.

Carbamates are relatively insoluble in water

but may be formulated with organic solvents

as emulsifiable concentrates to provide oil-inwater emulsions for low- or high-gallonage applications. Carbamates are moderately volatile,

and their activity may decrease rapidly at high

temperatures. Activity may also decrease at

high soil moistures. Oral toxicities of carbamates to rats are low; LD-,« values range from

720 to 5,000 milligrams per kilogram of body

weight.

Propanil

Propanil is relatively insoluble in water, but

it is formulated with organic solvents as an

emulsifiable concentrate. It forms oil-in-water

emulsions and is slightly volatile at high temperatures. It has low oral toxicity for rats; the

LD,o ranges from 1,200 to 2,300 milligrams per

kilogram of body weight.

New Herbicides

Research is being continued to improve current weed-control practices and to develop new

herbicides and new, improved chemical-cultural

methods of controlling weeds in rice. Three

herbicides that recently have shown outstanding experimental performance for controlling

grass weeds in rice are swep, molinate, and

4-chlorobenzenesulfono-2-toluidide. They have

not been approved for use on rice.

Swep gives both preemergence and early

postemergence control of many grass and

broadleaf weeds, including barnyardgrass,

brachiaria, crabgrass, sesbania, curly indigo,

and Mexican-weed. Swep was most effective

when applied at rates of 4 to 6 pounds in 10 to

20 gallons of water per acre. Higher application rates were harmful to the rice crop, and

lower rates did not control the grass weeds.

Swep controlled grass weeds best when applied to grass plants having 1 or 2 leaves.

Treatment immediately after seeding was less

effective than treatment at weed emergence

Young rice plants were tolerant to swep, but

older ones (those with two or more leaves)

were sometimes injured.
10 AGR. HANDB. 292, U.S. DEPT. OF AGRICULTURE

Swep controlled grass weeds for 10 to 14

days after spraying if the soil contained enough

moisture to activate the swep. When sprayed

onto barnyardgrass in the 1- to 2-leaf stages,

it killed the plants that were up and controlled

barnyardgrass that emerged during the following 10 to 14 days. Flooding at the end of this

period was necessary to prevent barnyardgrass

emergence and reinfestation.

Commercially grown varieties of rice are

tolerant to swep. Field experiments indicated

that swep injured dry-seeded rice (drilled or

broadcast) less than water-seeded rice.

Molinate controlled barnyardgrass in experiments in California and Arkansas. In California, molinate at 2 to 12 pounds per acre applied

as a preplant soil-incorporated treatment

effectively controlled barnyardgrass and did not

injure rice. Emulsifiable concentrate and

granular formulations of molinate controlled

barnyardgrass effectively, if the soil was dry at

treatment. Soil incorporation or flooding within

12 hours after application prevented loss of

the herbicide from the soil by volatilization.

If the soil was moist at treatment, the herbicide

had to be incorporated immediately after application to prevent loss from the soil. In Arkansas, preplant soil-incorporated applications of

molinate at 2 to 8 pounds per acre controlled

barnyardgrass but injured rice somewhat.

Postemergence water-applied treatments of

granular molinate at 4 pounds per acre effectively controlled barnyardgrass and did not

injure rice. In this experiment molinate was

broadcast onto the water when barnyardgrass

plants had 2 or 3 leaves and the rice had 1 or 2

leaves.

Investigations in Arkansas indicated that 4-

chlorobenzenesulfono-2-toluidide controls barnyardgrass and other grass weeds when applied

before they emerge. Application rates of 4 to

6 pounds per acre controlled grass weeds effectively and did not injure rice. Grass weeds

were controlled most effectively when the herbicide treatment was followed immediately by

flooding. Barnyardgrass sprayed with 4-chIorobenzenesulfono-2-toluidide turned red 3 to 7

days after treatment.

General Precautions for Using

Herbicides

Drift Hazards

PHENOXY HERBICIDES.—Caution should be

used when spraying 2,4-D, MCPA, 2,4,5-T, and

silvex to control broadleaf weeds in rice since

these herbicides are very toxic to crops, such

as cotton, soybeans, and tomatoes, and to

valuable trees, shrubs, and ornamental plants.

These herbicides should not be sprayed when

the wind is blowing more than 5 miles per hour.

Ricegrowing States specify wind-velocity limits

for tractor and aerial spraying.

Cotton and soybeans are injured more

severely by some phenoxy herbicides than by

others. Cotton is injured most severely by

2,4-D, followed by MCPA, silvex, and 2,4,5-T

in decreasing order. Soybeans are injured most

severely by silvex, followed by 2,4,5-T and

2,4-D in decreasing order. Cotton and soybeans are normally injured less by amine salt

formulations of phenoxy herbicides than by

esters.

Spray from amine salts and low-volatile

esters usually drifts to susceptible crops or

plants during the spraying operation and not

afterward. At temperatures above 95° F., lowvolatile ester formulations may volatilize after

spraying. The vapors may injure nearby

susceptible crops.

All major rice-producing States regulate

aerial spraying of phenoxy herbicides. Most

States also regulate ground applications. Before spraying rice with postemergence herbicides, farmers and custom applicators should

become familiar with State regulations concerning equipment, herbicide formulations,

wind velocity, records, responsibility, and liability.

PROPANIL.—Field crops, such as cotton and

soybeans, and certain horticultural and ornamental plants are injured by spray drift of

propanil. Propanil is not so toxic to these

plants as phenoxy herbicides, but spray drift to

nearby susceptible plants should be prevented.

Application of propanil by aerial equipment

causes greater drift than application by ground

equipment. When aerial equipment is used,

special attention should be given to wind velocity and direction to avoid spray drift on

neai'by susceptible plants. Spraying is best

when wind velocity is not more than 5 miles

per hour. Propanil should not be sprayed when

wind velocity exceeds 10 miles per hour. If the

susceptible crop is located upwind from the

rice, spraying may be done safely in a 1 to 10

mile per hour wind within 100 to 200 feet of

the susceptible crop. If the sensitive crop is

downwind from the rice, the safe distance is at

least one-half mile.

Propanil may kill young cotton and soybean

plants and severely injure older ones. Cotton

and soybean plants are very susceptible to

propanil from the time they emerge until they

are 8 to 10 inches tall. Usually one-half pound

per acre is required to injure them severely

enough to reduce yields greatly. Propanil injury on cotton and soybean plants appears as
WEEDS AND THEIR CONTROL IN RICE PRODUCTION 11

brown and yellow mottling on the leaves, and

as necrosis along- leaf margins; often the leaves

and whole plants are killed. If the plants are

not killed, they usually grow new leaves, recover vegetatively, and produce nearly normal

yields. Older plants recover more quickly and

completely than do younger ones.

Residue Hazards

In addition to State laws regulating application of herbicides, Federal laws provide for

establishing safe tolerances for residues of

herbicides on raw agricultural pi'oducts. Both

rough and milled rice are classed as raw agricultural products. Herbicides that leave no

residue may be used on rice without regard to

the tolerance. Propanil, 2,4-D, MCPA, 2,4,5-T,

silvex, and CIPC leave no residue if used according to directions on the label.

The directions for using a pesticide, which

appear on the label, are subject to clearance

under a Federal law known as the Insecticide,

Fungicide, and Rodenticide Act. Clearance is

withheld if, on the basis of experimental evidence, the usage proposed may contribute residue in excess of the applicable tolerance. In

the event no tolerance or exemption exists for

the pesticide, clearance is withheld if the

proposed usage would likely contribute any

residue. The joint opinion of the Pesticides

Regulation Division of the U.S. Department of

Agriculture and of the Food and Drug Administration of the Department of Health, Education, and Welfare is that labels of pesticides in

commercial usage should generally furnish a

reliable guide so as to avoid excessive residues (107).

Storage

A herbicide with a low flash point (140° F.

or less) is dangerous in storage. Herbicides

used for weed control in rice have relatively

high flash points; hence, they may be stored

safely without hazard of fire.

Deterioration of herbicides in storage can be

prevented by observing certain precautions.

Dust and wettable powders should be stored in

a dry place. If they get wet, they may cake and

the packages may deteriorate. Water-soluble

solids also may cake when wet and when subjected to great changes in temperature. If

packages are left open, hygroscopic chemicals

become wet by absorbing water from moist air.

It is essential, therefore, to close herbicide

packages tightly for storage.

Liquid formulations should be stored on

pallets or duckboards to prevent rusting of the

metal containers. Containers should be kept

closed tightly and air vents—punched to facilitate pouring—should be plugged. Small

amounts of water introduced into emulsifiable

concentrates or oil solutions may cause the

solution to jell or may cause deterioration of

the container.

Liquid herbicides may crystallize or precipitate at temperatures below 32° F. If this happens, the solution should be heated to 40° or

slightly higher, and the containers should be

rolled or shaken. If the crystals return to solution, the herbicide is then usually good; but

the herbicide should not be used if the crystals

do not dissolve. Phenoxy herbicides and propanil should not be stored at temperatures

below 15°.

Liquid herbicides may deteriorate at temperatures above 95° F. In addition, herbicides

stored in drums may expand at high temperatures and cause bulging and leaking of the containers. High temperatures also may reduce

the effectiveness of emulsifiers and hasten the

corrosion of containers. Drums of herbicides

stored in the direct sun become excessively hot,

especially during hot weather. Herbicides

should be stored in well-ventilated buildings or

sheds during hot weather.

Safety in Handling

Herbicides used for commercial weed control

in rice are relatively nontoxic to humans and

Avarm-blooded animals. Caution, however,

should be used when mixing, applying, or disposing of herbicides to prevent contact with

the herbicide. Propanil may be especially irritating to the skin and eyes. If the concentrated

herbicide is accidentally spilled on the skin or

in the eyes, the skin or eyes should be flooded

promptly and thoroughly with water.

The spray mixture may be irritating, especially to the eyes. Mixing crews, flagmen, and

applicators should avoid breathing fumes and

spray mist and should be careful that the spray

does not come in contact with the eyes and

skin. If repeated and prolonged exposure is

likely, goggles and protective clothmg should

be worn.

To protect fish and wildlife, care should be

taken not to contaminate ponds, lakes, or

streams while mixing, applying, or disposing ot

herbicides. Herbicides should not be stored

near feed or food.

Cleaning Spray Equipment

Sprav equipment used to apply phenoxy

herbicides should not be used to apply other

chemicals to cotton, tomatoes, or other plants

because these herbicides are difficult to remove
12 AGR. HANDB. 292, U.S. DEPT. OF AGRICULTURE

from the sprayer and even traces left in the

sprayer will cause serious damage. After

thorough cleaning, however, the same sprayer

used for phenoxy herbicides may be used to

apply fungicides, insecticides, and other herbicides on moderately sensitive crops, including

soybeans, clover, and lespedeza.

Thorough cleaning of a sprayer with warm

water and a detergent should remove most of

the herbicide remaining in the sprayer. Further

cleaning may be accomplished with a solution

of 1 part household ammonia in 100 parts of

water. This solution should remain in the tank,

including hose and boom, for 12 to 24 hours.

The equipment then should be thoroughly

rinsed with clean water.

Activated charcoal is one of the most effective agents for cleaning herbicides from spray

equipment. It has the advantage of being a

faster and more effective cleaning agent than

household ammonia. Phenoxy herbicides can

be removed by rinsing the sprayer for about

2 minutes with a 1-percent suspension of activated charcoal followed by a rinse of clean

water. A desirable solution may be made by

mixing 1 pound of finely ground activated charcoal in 12 gallons of water containing a detergent.

To be sure the sprayer contains no herbicide, the operator may fill the sprayer with

water and spray seedlings of a sensitive plant,

such as bean, tomato, or morningglory. If the

seedlings are not affected within 1 or 2 days,

the equipment is safe for further use.

Spray equipment used for propanil can be

used safely for other spraying purposes if all

parts are cleaned thoroughly with water and

detergent and then rinsed several times with

clean water. All parts of the sprayer, including hose, pump, boom, and nozzles, should be

cleaned thoroughly.

Principles of Controlling Weeds

With Herbicides

Controlling Grass and Broadleaf

Weeds With Propanil

Propanil controls barnyardgrass. including

species of Echinochloa crusgalli, E. colonum,

and E. cnispavonis, and other grasses, including crabgrass (Digitaria spp.), Texas-millet

(Panicum texanum Buckl.), paragrass (P. pnrpurascens Raddi.), and brachiaria. Propanil

also controls certain young annual broadleaf

weeds, such as sesbania, curly indigo, gooseweed, redstem, and waterplantain. and young

annual sedges, such as spikerush, umbrellasedge, fimbristylis, and rough-seed bulrush.

These weeds are most effectively controlled

when they are in the early vegetative stage of

growth.

MODE OF ACTION.—Propanil is a selective

postemergence herbicide for gi'ass and broadleaf weeds. It is usually applied when the

weeds and rice are in the early stages of

development. Propanil apparently kills the cells

of grass and broadleaf plants by contact action.

Investigations in the United States with a

radioactive isotope indicated that propanil was

not translocated appreciably either upward or

downward in either rice or barnyardgrass (58).

Work in Japan, however, showed that propanil

was translocated rapidly upward but slowly

downward (101). Propanil applied to leaf

apexes of barnyardgrass killed only the cells

at the leaf tip, but that applied to the leaf

sheath killed the treated leaf and subsequent

new leaves. This may explain the need for

completely covering the grass plants in field

treatments. Propanil activity on barnyardgrass progressed from cell to cell in an apical

direction (101).

Absorption and translocation differences in

rice and barnyardgrass do not explain the

basis of selectivity of propanil. The basis of

selectivity is undoubtedly physiological or biochemical.

RATE OF APPLICATION.—Propanil at 3 to 4

pounds per acre applied at the correct time controls most annual grass weeds (fig. 1). In a

field experiment in Arkansas, propanil at 3, 5,

and 7 pounds per acre was applied to barnyardgrass having 2 or 3 leaves (fig. 2). Barnyardgrass having 2 or 3 leaves was controlled well

enough with 3 pounds of propanil to produce

nearly maximum yields of rice (table 5). In

another investigation in Arkansas, propanil at

2 pounds per acre applied to barnyardgrass

having 1 to 3 leaves gave somewhat less control

than did rates of 3 pounds or more (table 6).

Results from these experiments in Arkansas

are indicative of experimental results obtained

from California, Louisiana, Mississippi, and

Texas.

A temporary chlorosis and tipburn on rice

leaves may occur soon after treatment with

propanil at rates of 3 or 4 pounds per acre,

but no permanent injury to rice occurs even

with rates as high as 12 pounds. New leaves

that emerge after treatment normally show no

signs of injury. Injury on rice is more pronounced and persists longer when the soil is

very dry and when temperatures are either

extremely low (daily lows below 50° F.) or

extremely high (daily highs above 95°) at the

time of treatment; but even when injury is

pronounced, rice plants outgrow damage within

5 to 10 days after treatment.
WEEDS AND THEIR CONTROL IN RICE PRODUCTION 13

' I

f/ ,"^ '

FIGURE 1.—Control of barnyardgrass in rice with propanil : Left, Plot sprayed with propanil at 4 pounds per acre

when barnyardgrass had 2 or 3 leaves; right, unsprayed plot.

FIGURE 2.-Growth stages of barnyardgrass: Left to right, Plants in the 1-, 2-, 3-, 4-, and 5-leaf and tillering stanes.
14 AGR. HANDB. 292, U.S. DEPT. OF AGRICULTURE

TABLE 5.—Effect of time and rate of application of propanil on control of barnyardgrass and yield

of rice groivn in the field, Stuttgart, Ark., 1960

Control of barnyardgrass Yield of rice, per acre

Stage or height of grass at time

of spraying

When rate of propanil

applied per acre was—

Average

When rate of propanil

applied per acre was—

3

pounds

5

pounds

7

pounds

3

pounds

5

pounds

7

pounds

Average'

Immediately after seeding

Percent

17

58

80

Percent

18

52

84

Percent

15

64

88

Percent

17

58

84

Pounds

2,320

4,100

4,640

Pounds

2,660

3,720

4,700

Pounds

2,930

4,100

4,630

Pounds

2,640

1-leaf, Yi inch 3,970

2- and 3-leaf, 2 inches 4,660

L.S.D. at 5-percent level 8

11

330

L.S.D. at 1-percent level 440

' The hoed and unhoed checks yielded 4,720 and 2,640 pounds per acre, respectively.

TABLE 6.—Effect of rate of application of propanil on control of barnyardgrass and

yield of rice grown in the field at two locations in Arkansas, 1961

(Propanil applied at early postemergence; barnyardgrass

had 2 or 3 leaves]

Location of experiment

and rate of propanil

per acre

Control of

barnyardgrass

Yield of

rice, per

acre'

Kelso:=

None (check)..- .-

Percent

5

70

85

85

88

83

87

5

70

78

86

91

96

99

Pounds

2,460

2 pounds

3 pounds _.

3,110

3,320

5 pounds 3,380

7 pounds .- __ 3,400

9 pounds 3,410

12 pounds .- 3,730

Keiser:'

None (check) 3,490

2 pounds 3,840

3 pounds 3,700

5 pounds . 4,000

7 pounds 3,860

9 pounds -- -- 3,930

12 pounds - 3,590

• Propanil-treated plots yielded significantly more rice

than the check, but yield from plots treated with different

rates did not differ significantly.

- Propanil-treated plots had significantly less barnyardgrass, but control of barnyardgrass on plots treated with

different rates did not differ significantly.

' L.S.D. for control of barnyardgrass: at 5-percent level,

10 percent; at 1-percent level, 14 percent.

TIME OF APPLICATION.—Propanil applied as

a preplanting or a preemergence treatment

does not control grass weeds or injure rice

(table 5). It controls barnyardgrass most

effectively when applied to grass in the 2- or

3-leaf stage, or 2 to 3 inches tall (fig. 2; tables

5 and 7). Propanil applied at 8 to 9 pounds

per acre to barnyardgrass 6 inches tall or more

usually does not control it satisfactorily. Rapidgrowing and succulent grass weeds, however,

may be controlled when they have 4 leaves or

more. In a field experiment in 1961, barnyardgrass was controlled progressively less as it

increased in size from 1/2 to 2 inches tall to 10

to 36 inches tall (table 7). Control of barnyardgrass also decreased in 1962 when propanil

was applied during the first four stages of

growth, but control was better when it was

applied at the last two stages than when it was

applied at the fourth stage (table 7). The high

degree of control at the last two stages in 1962

was the result of an application of nitrogen

immediately after the fourth treatment, which

made the grass grow rapidly. Thus, rapidly

growing grass, even though it was large, was

more susceptible to propanil than was grass

growing more fflowly. The results of these experiments indicate the importance of the

growth rate of weeds when propanil is used.

Grass weeds in the 1-leaf stage are killed by

propanil, but plants that emerge afterward

may reinfest the ricefield. For example, propanil gave only 58-percent control of barnyardgrass when applied to grass weeds in the 1-leaf

stage (table 5). Emerged grass was killed, but

that emerging after spraying reinfested the

plots. Usually most of the grass weeds will

have emerged by the time the oldest grass
WEEDS AND THEIR CONTROL IN RICE PRODUCTION 15

TABLE 7.—Effect of time of application of propanil on control of barnyardgrass and yield,

of rice, Stuttgart, Ark., 1961-62

[Values are averages from plots treated with 3, 5, 7, and 9

pounds of propanil per acre]

Height or stage of

grass at time of

spraying

Yi to 2 inches, or 2- to

4-leaf

Yi to 7 inches, or 2-leaf

to early tillering

2 to 8 inches, or early

tillering

6 to 13 inches, or late

tillering

10 to 20 inches, or beginning to head

15 to 36 inches, or heading

Not sprayed (check)

L.S.D. at 5-percent

level

L.S.D. at 1-percent

level

Control of

barnyardgrass

1961 1962

Percent

69

60

48

17

0

10

0

11

16

Perceni

100

82

50

22

42

46

0

16

23

Yield of rice,

per acre

1961

Pounds

3,720

3,570

3,440

2,700

2,310

2,530

2,340

440

630

1962

Pounds

4,680

4,530

3,950

3,070

3,510

3,380

2,010

890

1,060

reaches the 3-leaf stage. Because propanil has

no preemergence activity, it should not be applied until all grass weeds have emerged.

Propanil should be applied according to the

developmental stage of the grass weeds rather

than the rice. When barnyardgrass has 2 or 3

leaves, rice usually has 1 or 2 leaves, but it may

be just emerging or may have 3 leaves or more.

However, there should be a reasonable stand of

rice before treatment. If the crop has to be

replanted for any reason, the propanil application will be wasted.

WATER MANAGEMENT.—Irrigating the ricefield before treatment with propanil may be

necessary during dry, hot weather. In experiments in Arkansas in May 1962, rice was seeded

when the soil had sufficient moisture for germination of rice and barnyardgrass. No rain fell

from planting time until spraying time (11

days). The barnyardgrass seedlings were growing slowly in the dry soil, and many seedlings

were not killed by propanil. Barnyardgrass

plants with 1 to 3 leaves were usually killed

even though they were growing slowly, but

those with 4 or more leaves and those with

tillers were not killed. When the soil is dry and

crusty, irrigation of the ricefields a few days

before spraying stimulates grass weeds and

makes them more susceptible to propanil.

Water should not be standing on fields when

they are treated with propanil. Weeds covered

with water are not killed because propanil cannot contact them. Moist or puddled soil is

desirable because grass weeds are presumably

growing rapidly when moisture is adequate.

Fields treated with propanil should be

flooded 1 to 4 days after treatment to prevent

barnyardgrass or other grass-weed plants from

reinfesting the field to compete with rice and

cause severe yield losses. Flooding the ricefield

immediately after treatment sometimes increases the activity of propanil on barnyardgrass.

Some commercial fields of rice are so large

that timely flooding after treatment with propanil may be difliicult. If all of a large field is

sprayed at once, grass weeds may reinfest the

field before it can be flooded, especially if the

water supply is limited. Large fields should be

divided so that they can be flooded with the

available water supply on the farm within 1 to

4 days after spraying. Field size should be

keyed to water supply before the rice is planted

and not after the rice has emerged and is ready

for spraying.

METHOD AND DEPTH OF SEEDING.—Propanil

at 2, 4, 8, and 16 pounds per acre applied to

varieties Bluebonnet 50 and Nato in the 1- and

2-leaf stages grown in the greenhouse at Stuttgart, Ark., did not injure either variety regardless of method or depth of seeding, but 32

pounds injured both varieties moderately

(table 8). Field-grown Bluebonnet 50 that was

sprayed with propanil when it was in the 1- to

2-leaf stage was not injured (table 9). Thus,

method and depth of seeding rice do not affect

the activity of propanil on rice.

METHOD OF APPLICATION.—Propanil may be

applied in the field with ground or aerial equipment. Boom-nozzle sprayers are more satisfactory for ground applications than are other

types of sprayers. Boom-nozzle, venturi, and

rotary-atomizer sprayers, when properly adjusted and operated, are satisfactory for aerial

applications. Aerial equipment is more satisfactory than ground equipment because quick

and timely applications can be made even

though the field may be too wet to support

ground equipment. Moreover, levees present a

problem with ground-operated equipment.

Droplets from 200 to 400 microns in diameter

are considered optimum for ground applications. Droplets that range from 200 to 300

microns in diameter while in the air are considered optimum for aerial applications.

The spray pattern of aerial and ground

equipment should be checked carefully before

spraying to insure uniform spray applications.
16 AGR. HANDB. 292, U.S. DEPT. OF AGRICULTURE

TABLE 8.—Effect of method and depth of seeding of rice and rate of propanil as an early postemergence application on growth of tivo varieties of rice tinder greenhouse conditions, Stuttgart, Ark., 1959

Injury rating of rice when rate ol propanil applied per acre was'—

Variety and method and depth of seeding

0 2 pounds 4 pounds 8 pounds 16 pounds 32 pounds

Nato:

Water seeding. 0

0

0

0

0

0

0

2

0

0

0

0

0

0

0

0

0

0

1.3

0

0

0

,7

0

1.7

1.3

1.3

2.3

6.0

Dry seeding, 1-2 inch

Dry seeding, 13^ inch

Bluebonnet 50:

Water seeding _

3.7

2.7

3.7

Dry seeding, }4 inch

Dry seeding, 1J4 inch

4.3

1.3

Rated as follows: 0, no injury; 1-3, slight injury; 4-6, moderate injury; 7-9, severe injury; 10, all plants killed,

TABLE 9.—Effect of method and depth of seeding of rice and rate of propanil as an early

postemergence application on yield, of Bluebonnet 50 rice grown in the field, Stuttgart, Ark., 1960

Yield of rice, per acre'

Method and depth

of seeding

Rate of propanil applied,

per acre

3

pounds

6

pounds

12

pounds

Average

Water seeding;

soil surface

Drilling;

1 }/2 inches

Broadcasting;

3^2 to 1J4 inches

Percent

101

102

108

Percent

102

105

105

Percent

106

104

109

Percent

103

104

107

' Yields expressed as percentage of weed-free check. Yields

for water seeding, drilling, and broadcasting treatments in

the untreated weed-free checks were 5,630, 5,310, and 5,220

pounds per acre, respectively.

When aerial equipment is used, the swath

should be about equal to the wing span of the

aircraft or, preferably, slightly less but it may

vary with type of aircraft and spray equipment. A swath of 30 to 40 feet is generally

used. Grass and broadleaf weeds are controlled

satisfactorily with propanil when the spray

solution covers the weeds adequately and uniformly.

SPRAY VOLUME.—Because of the mode of

action of propanil, uniform coverage of the

exposed part of grass and broadleaf weeds is

necessary for satisfactory control. The same

amount of chemical per leaf is more effective

in many well-distributed droplets than in one

large drop.

Ground sprayers should apply propanil at

3 or 4 pounds per acre in 15 to 20 gallons per

acre of herbicide-water solution. In one field

experiment in Arkansas, propanil at 3 pounds

per acre applied by tractor-drawn equipment in

spray solutions of 5, 10, 20, and 40 gallons per

acre controlled barnyardgrass, and rice was

uninjured at all volumes. Ground equipment

in a field experiment in Texas, however, controlled 99 percent of the grass weeds when

propanil at 3 pounds per acre was applied in

a spray solution of 10 gallons per acre but

only 90 and 66 percent at the same rate when

applied in solutions of 8 and 5 gallons per acre.

Other experiments and observations suggest

that propanil at 3 or 4 pounds per acre applied

by ground equipment controls barnyardgrass

and broadleaf weeds more efliectively when

applied in herbicide-water solutions of 15 to 20

gallons per acre than when applied at lower

volumes.

A spray volume of at least 10 gallons per

acre of herbicide-water solution is generally

used for aerial applications of propanil. A

volume of 12 to 15 gallons per acre may be

required for very dense stands of grass with 4

leaves or more. In an experiment at Stuttgart,

Ark., with boom-nozzle aerial applications, propanil at 3 pounds per acre in 5 gallons per acre

of herbicide-water solution was less effective on

grass weeds than a similar rate in 10 gallons

per acre. In another field study at Stuttgart,

propanil at 3 to 4 pounds per acre applied by

boom-nozzle aerial equipment in 5 to 10 gallons
WEEDS AND THEIR CONTROL IN RICE PRODUCTION 17

per acre of spray solution controlled barnyardgrass and did not injure rice. Spray drift was

less with 10 than with 5 gallons.

SOIL TYPE.—Propanil applied to rice grown

on the major rice soils, including silt loam and

clays, controls grass weeds satisfactorily

(table 10). Soil type, apparently, does not

change the effectiveness of propanil on grass

weeds, probably because of the postemergence

action of propanil on grass plants.

TABLE 10.—Ejfect of soil type on propanil activity, Arkansas, 1960-61

[Propanil applied when weed grasses had 2 or 3 leaves]

Control

of barnyardgrass on

treated

plot'

Yield of rice, per acre

Soil type

Untreated Treated'

Increase

for

treated

plot

Crowley silt

loam_

Sharkey clay___

Perry clay

Percent

82

82

85

Pounds

2,610

3,490

2,460

Pounds

4,670

3,850

3,350

Percent

79

11

36

' Values are averages from plots treated with 3 and 5

pounds of propanil per acre.

RICE VARIETY.—Almost all varieties of rice

are tolerant to propanil. In field investigations,

Bluebonnet 50, Caloro, Century Patna 231,

Gulfrose, Nato, Northrose, and Zenith—all in

the 2- to 3-leaf stages—were uninjured by 3 to

6 pounds per acre of propanil (table 11). At

equivalent stages of growth, Belle Patna and

Texas Patna 49 varieties were also uninjured

by 3 to 6 pounds per acre of propanil. Commercial varieties in all ricegrowing areas were

not injured by postemergence applications of

propanil in 1961-63.

WEATHER CONDITIONS.—Grass and broadleaf

weeds respond best to propanil when temperatures are moderate, or when daily maximum

temperatures range from 70° to 90° F. Low

temperatures during the week before spraying

often slow weed growth and retard propanil

activity. If daily minimum temperatures are

below 50° for a few days just before treatment,

propanil activity is retarded. In addition, if

daiïy maximum temperatures do not exceed

70°, propanil activity may be reduced. For

maximum effectiveness on grass weeds propanil

should not be sprayed when temperatures are

extremely low.

Extremely high temperatures enhance the

activity of propanil on rice; thus, selectivity is

TABLE n.~Effect of early postemergence an

plications of propanil at 3 to 6 pounds per

acre on yield, of several varieties of rice

Stuttgart, Ark., 1960-61

Yield of rice'

Variety

1960'^ 1961'^ AverageBluebonnet 50.

Percent

98

95

100

92

100

99

93

Percent

98

101

102

95

105

103

101

Percent

98

98

101

94

102

101

97

Caloro.

Century Patna 231

Gulfrose.-

Nato

Northrose

Zenith

' Yield expressed as percentage of the untreated weedfree check for each year and variety.

2 No significant differences among varieties.

reduced. Propanil at 3 to 4 pounds per acre

injured rice severely where daily maximum temperatures were above 95° F. for several days

before spraying, especially where rice plants

were under drought stress. In addition, extremely high temperatures may retard the rate

of weed growth, which increases their tolerance

to propanil. For maximum safety to rice and

for optimum effectiveness on weeds, propanil

should not be sprayed when temperatures are

extremely high (95° or above).

A period of 8 to 12 hours without rain is

required after treatment for effective control

of grass weeds with propanil. Rain occurring

soon after treatment may wash off the propanil

and reduce its activity on grass weeds. Spraying, therefore, should be delayed until the

threat of rain has passed.

EFFECT OF INSECTICIDES.—Propanil and insecticides, such as carbaryl, methyl and ethyl

parathion, and toxaphene, applied to rice within

14 days of each other may kill rice plants and

reduce stands. Rice has been burned and killed

where the interval was 7 to 9 days. Rice may

be damaged when insecticides are applied

either before or after an application of propanil. Carbamate and phosphate insecticides

consistently burn and kill rice plants when applied during a period of 14 days before or 14

days after a propanil treatment. Chlorinated

hydrocarbon insecticides, such as endrin, dieldrin, aldrin, heptachlor, and DDT, cause less

phytotoxicity on rice than other insecticides,

but considerable yellowing and burning of the

rice foliage may result. These chlorinated hydrocarbon insecticides may be safely applied

7 days before or 7 days after a propanil treat-
18 AGR. HANDB. 292, U.S. DEPT. OF AGRICULTURE

ment. Rice that has been treated with aldrin

as a seed treatment may be safely sprayed with

propanil.

Controlling Grass Weeds With CIPC

MODE OF ACTION.—CIPC is a selective preemergence and postemergence grass-weed

killer. It is usually applied immediately after

emergence of grass weeds in ricefields. CIPC

strongly inhibits growth of germinated seedlings of most grass plants. It is usually absorbed by the roots of grass plants, but it may

give some postemergence contact kill of young

weeds as foliage sprays. Rice also will absorb

CIPC through its roots and may be killed.

Selectivity, therefore, is obtained by placing

the rice seed so that the rice roots grow in

untreated soil below the treated surface. Grass

weeds that emerge near the soil surface, however, have roots located in the treated soil; the

roots absorb the herbicide, and weeds are

killed. Selectivity is also obtained because the

roots of grass weeds tend to develop near the

soil surface whereas rice roots develop from

nodes deeper in the soil. CIPC also kills grassweed seedlings that may germinate or emerge

after spraying. CIPC usually gives residual

control of grass weeds for about 1 week after

spraying, provided soil moisture is ample.

CIPC-treated plants develop a thick, short

coleoptile. Initial symptoms of CIPC injury

include a dark, blue-green color followed by a

yellow-brown color as the plant nears death.

CIPC affects cell division, cell elongation, and

certain physiological and metabolic processes,

such as respiration, enzyme systems, and carbohydrate metabolism.

FORMULATIONS AND RATE.—Emulsifiable and

granular formulations of CIPC were compared

in experiments in Arkansas where a 5-percent

granular (Attaclay, RVM, 24-48 mesh) formulation of CIPC was broadcast by hand at 5 to

7 pounds of actual CIPC per acre and an emulsifiable formulation was sprayed at 6 pounds

per acre. The treatments were made when the

rice had 2 leaves and the barnyardgrass had 1

to 3 leaves. Rainfall soon after application

washed the granules into the low areas of the

plots; this resulted in a low rate in the high

areas and a high rate in the low areas. Uneven

distribution of the granular CIPC caused somewhat uneven control of barnyardgrass. The

granular formulation controlled 50 to 60 percent of the barnyardgrass, and the emulsifiable

formulation controlled 60 to 70 percent of the

barnyardgrass. Since the seedlings of barnyardgrass were rather large at time of treatment, some were killed; others were inhibited

severely, which reduced their competitiveness

with rice. Plots treated with granular and

emulsifiable formulations yielded an average of

4,640 and 4,590 pounds of rough rice per acre,

respectively, as compared with 3,500 pounds

for the untreated plots. Both formulations,

therefore, were effective in reducing barnyardgrass competition with rice. For commercial

field applications the emulsifiable formulation

is generally more effective and practical than

granules. This is because the emulsifiable

formulation kills emerged barnyardgrass seedlings by contact, and it is not moved by irrigation water.

The effect of CIPC applied at different rates

was studied over a 5-year period in Arkansas

(table 12). Generally, as the rate of CIPC was

TABLE 12.—Effect of rate of application of CIPC on control of barnyardgrass and yield of rice,

Stuttgart, Ark., 1956-60

ICIPC applied when barnyardgrass had 1 leaf. All plots were irrigated (flushed) a few days after treatment]

Control of barnyardgrass Yield of rice, per acre

Rate per acre

1956 1957 1958 1959 1960

Average 1956 1957 1958 1959 1960

Average

Untreated check

Percent

0

Percent

0

Percent

0

Percent

0

43

83

88

Percent

0

70

80

85

Percent

0

56

68

77

79

86

Pounds

1,660

Pounds

2,510

Pounds

2,270

Pounds

590

2,660

4,510

4,550

Pounds

390

4,620

4,310

5,140

Pounds

1,480

3,640

73

70

83

72

82

93

98

30

58

62

75

4,200

3,810

3,570

4,100

4,340

4,500

4,510

3,450

3,830

4,000

4,460

4,110

fi nounds 4,330

4,030

1 ft nniinH<5 4,490

L.S.D. at 5-percent

7 8 13 20 12 500 260 360 750 1,030 580

_
WEEDS AND THEIR CONTROL IN RICE PRODUCTION 19

increased, barnyardgrass was controlled more

effectively. In 1956 and 1957 all rates controlled 70 percent or more of the barnyardgrass. In 1958 CIPC at 4 pounds per acre did

not control barnyardgrass satisfactorily, but

at 6, 8, and 10 pounds control was satisfactory.

In 1959 CIPC at 2 pounds per acre controlled

only 43 percent of the barnyardgrass, but in

1960 this rate controlled 70 percent. In 1960

the temperature was unseasonably cool after

treatment, which increased the activity of

CIPC. CIPC at 4 and 6 pounds in 1959 and

1960 controlled more than 80 percent of the

barnyardgrass.

Yields of rice may be greatly increased by

controlling grass with CIPC on areas where

infestations of barnyardgrass are heavy (table

12). CIPC at 6 and 8 pounds per acre usually

controlled sufficient barnyardgrass to permit

the production of nearly maximum yields of

rice (fig. 3). CIPC at rates lower than 6 pounds

did not control barnyardgrass during most

years, and at rates higher than 8 pounds returns did not justify the increased rate even if

the higher rate did not injure the rice.

TIME OF APPLICATION.—Rice and barnyardgrass were treated in experiments in Arkansas

with CIPC at the stages of growth indicated

'.:^i?íí5í,Í.V^Yl

/

FIGURE 3.—Control of barnyardgrass in rice with CIPC : Left, Plots sprayed early postemergence with CIPC at 6

pounds per acre; right, unsprayed.
20 AGR. HANDB. 292, U.S. DEPT. OF AGRICULTURE

in table 13. On both the Crowley silt loam and

Sharkey clay, barnyardgrass was controlled

best by applying CIPC at complete emergence

of rice when the grass had 1 to 2 leaves and

was 1/2 to 2 inches tall (table 13 and fig. 2).

CIPC applied immediately after seeding inhibited growth of rice seedlings and reduced

stands of rice when rainfall occurred soon after

treatment. CIPC applied to rice at emergence

caused slight burning or chlorosis along the

TABLE IS.—Effect of time of apjylication of CIPC on control of barmjardgrass and yield of rice,

Stuttgart, Ark., 1956-60

[CIPC applied at 4 to 8 pounds per acre]

Stage of rice at time Stage and height of

barnyardgrass at

time of treatment

Control of barnyardgrass Yield of rice, per acre

of treatment

1956' 1956' 1959' I960' 1956> 19562 1959' I960'

Untreated check

Preemergence

Just before emergence.

Emergence of 20-30

Untreated check

Preemergence

Coleoptile

1-leaf, 3 2-1 inch

1- and 2-leaf, 12-2

inches.

3- to 5-leaf, 2-4 inches

Tillering, 4-6 inches

Percent

0

66

68

70

75

Percent

0

4

Percent

0

Percent

0

38

Pounds

1,660

3,510

3,720

3,680

3,860

Pounds

1,930

2,030

Pounds

1,200

Pounds

2,640

3,.570

percent.

Complete emergence-.

Postemergence:

1 week

54 72

12

0

76

61

3,560 3,910

2,300

860

4,690

4,140

2 weeks

L.S.D. at 5-percent (») 11 8 {') 680 330

level.

' Experiment located on Crowley silt loam.

- Experiment located on Sharkey clay.

^ No significant differences among treatments excluding the untreated check.

margins and tips of the leaves. The rice seedlings, however, outgrew this injury soon after

treatment.

Time of applying CIPC is very critical if

maximum control of barnyardgrass is to be

obtained. Additionally, the comparative times

of emergence of rice and barnyardgrass vary

with temperature, soil moisture, soil type, and

possibly other factors. For these reasons, CIPC

applications should be based on the growth

stage of barnyardgrass rather than on that of

the rice. For example, if soil moisture is adequate and the soil temperature is cool immediately after seeding, barnyardgrass may

emerge before the rice, especially on clay soil.

If spray applications are made on the basis of

the stage of barnyardgrass, satisfactory control

may be obtained by treating immediately after

emergence of the first barnyardgrass. Rice

may range from preemergence to complete

emergence at this time.

Another advantage of applying CIPC according to the stage of growth of barnyardgrass is

that the seriousness of the infestation can be

determined before treatment. The need for

control can actually be determined before applying CIPC, which prevents using it unnecessarily on fields or parts of fields that are not

grassy.

METHOD AND DEPTH OF SEEDING.—In experiments in Arkansas, rice was seeded at three

depths and CIPC was applied at two rates immediately after the rice emerged (table 14).

All plots were kept free of weeds by hand

weeding and water management. The plots

were irrigated after treatment to keep the soil

moist, which should have allowed maximum

downward movement of CIPC in the soil. Both

rates of CIPC afi'ected the stand of rice less as

the seeds were placed deeper in the soil. In

1958 yields were reduced only on plots seeded

Va inch deep and sprayed with CIPC at 12

pounds per acre, but in 1959 yields were reduced on plots seeded 1/2 inch deep and sprayed

at both rates. Yield of rice seeded 1 and 2

inches deep was not reduced at either rate of

CIPC.

Rice has little tolerance to CIPC when roots

contact the herbicide. Rice must be seeded 1 to

2 inches deep in the soil to be protected from

injury. Barnyardgrass plants that come from

seed located in the upper inch layer of soil

contact the herbicides and are killed. The

deeper seeded rice is not injured because roots
WEEDS AND THEIR CONTROL IN RICE PRODUCTION 21

TABLE 14.—Effect of depth of seeding of rice and rate of application of CIPC as an early postemergence treatment on stand and yield of rice, Stuttgart, Ark., 1958-59

Depth of seeding rice and rate

Stand of rice' Yield of rice'

of CIPC per acre

1958 1959 Average 1958 1959 Average

}/2 inch:

6 pounds

12 pounds

1 inch:

6 pounds., . .

Percent

8

2

38

20

86

63

Percent

11

10

Percent

10

6

Percent

108

61

116

113

107

108

Percent

53

56

Percent

86

58

12 pounds

2 inches:

6 pounds

12 pounds..

85

64

86

64

114

123

110

116

' stand and yield of rice expressed as percentage of untreated weed-free check. Stands in 1958 and 1959 on the untreated

check were 35 and 17 plants per square foot, respectively; yields were 4,160 and 4,550 pounds per acre of rough

rice, respectively.

do not contact the herbicide. Weeds that germinate and emerge from depths greater than 2

inches are normally not controlled.

When weeds are to be controlled in rice with

CIPC, the crop should be drill seeded to a uniform depth of 2 inches. The seed may be

broadcast, but it should be incorporated uniformly in the upper 2 inches of soil and the

rate of seeding should be increased about onethird to compensate for seed located in the top

inch of soil. Rice plants that come from seed

located in the top inch of soil may be injured

severely or even killed. CIPC cannot be used

safely on rice seeded in water because most

of the roots are located at or near the surface

of the soil.

DOWNWARD MOVEMENT AND PERSISTENCE OF

CIPC IN RICE SOILS.—The downward movement of CIPC in rice soils in Arkansas was

studied in both the field and the greenhouse.

In 1957 pots in the greenhouse were filled with

Crowley silt loam and treated with CIPC at

6 and 12 pounds per acre. Water was applied

to the soil surface at rates equivalent to V2, 1,

and 2 inches of rain and in sufficient quantity

to flood the soil. The soil was divided into 1-

inch segments for sampling, and the cucumber

bioassay was used to determine the presence of

CIPC (97). All the CIPC was located in the

top 1-inch layer of soil.

Pots in another greenhouse study in 1958

were filled with Crowley silt loam and treated

with CIPC at 8 pounds per acre. Water was

applied at rates equivalent to 1, 2, and 2.6

inches of rain. The 2.6-inch quantity of water

inundated the soil. A chemical assay was used

to determine the presence of CIPC (35). The

0- to 1/2-, i/o- to 1-, and 1- to 2-inch layers of

soil contained 80, 20, and 0 percent of CIPC,

respectively.

The persistence of CIPC in a Crowley silt

loam was studied under field conditions in

Arkansas in 1958 and 1959. In 1958 CIPC at

0, 4, 8, 12, and 16 pounds per acre was applied

bi'oadcast to the soil. Samples were analyzed

at weekly intervals after treatment by using

both the cucumber and chemical assay methods.

Both assay methods indicated that CIPC was

gone from the soil in 2 weeks after treatment.

In 1959 CIPC at 0, 4, 8, and 12 pounds per

acre was applied broadcast to the soil. Some

plots were flooded and others remained dry

with only rainfall wetting them. Samples were

analyzed by the cucumber bioassay method at

weekly intervals after treatment. CIPC at

rates of 4, 8, and 12 pounds disappeared from

the soil in 3, 4, and 5 weeks, respectively. Deactivation was as fast when the soil was flooded

as when it was dry.

In summary, CIPC applied to the soil surface

was localized in the top 1-inch layer of soil

regardless of the quantity of water applied

after treatment. CIPC applied at 4 to 12

pounds per acre deactivated in 2 to 5 weeks

after its application to the soil.

WATER MANAGEMENT.—Irrigation must be

applied for CIPC to be effective when no ram

occurs soon after spraying. In 1957 when ramfall wet the soil, irrigation soon after treatment

did not increase the activity of CIPC (table

15). In 1958 when no rain occurred during the

10 days after treatment, irrigation increased

the activity of CIPC. Flooding soon after

spraying usually controlled barnyardgrass better than irrigation, but it injured rice more.
22 AGR. HANDß. 292, U.S. DEPT. OF AGRICULTURE

CIPC controlled barnyardgrass better in

1960 when plots were irrigated 1 day after

treatment than when they were flooded 8 days

after treatment (table 15). The field under the

latter treatment was kept flooded for 8 days,

drained, and let dry for 12 days during which

time barnyardgrass germinated and emerged.

Emergence of new barnyardgrass plants and

reinfestation of the field was prevented by

keeping rice flooded after treatment with CIPC.

In summary, ample soil moisture was necessary for effectively controlling weeds in rice

with CIPC. If the soil surface became dry or

sunbaked, irrigation was required to control

barnyardgrass with CIPC. Several irrigations

may be necessary to keep the soil moist for 10

to 14 days after treatment. To prevent reinfestation with barnyardgrass, the soil must

be flooded before CIPC disappears, which is

usually about 2 to 5 weeks after treatment.

TABLE 15.—Effect of water management after CIPC applications on control of barnyardgrass and

yield of rice, Stuttgart, Ark., 1957-60

IRice and barnyardgrass had 1 leaf at time of spraying. CIPC applied at 2 to 10 pounds per acre]

Year and water management'

1957:

Irrigated 1 day after spraying^.

Irrigated 6 days after sprayingFlooded 14 days after spraying.

Flooded 20 days after spraying.

L.S.D

1958:

Irrigated 2 days after spraying^

Flooded 2 days after spraying.

Flooded 12 days after spraying.

Flooded 21 days after spraying .

L.S.D. at 5-percent level__.

L.S.D. at 1-percent level. _.

1959:

Irrigated 2 days after spraying'

Flooded 2 days after spraying..

L.S.D. at 5-percent level...

1960:

Irrigated 1 day after spraying<'_

Flooded 8 days after sprayings.

L.S.D. at 5-percent level._.

Control of

barnyardgrass

Percent

86

87

92

81

{')

56

85

61

23

6

9

470

670

72

86

3,910

3,620

11 w

78

48

4,690

3,340

17

Yield of rice,

per acre

Pounds

4,020

3,940

4,030

3,990

0)

3,600

4,050

3,790

2,940

1,030

' Irrigated means flooding the soil and draining it as soon as it is saturated.

- Flooded 14 days after treatment.

' No significant difference.

< Flooded 23 days after treatment.

5 Flooded 20 days after treatment.

" Flooded 15 days after treatment.

Irrigation water applied soon after treatment

did not increase CIPC injury to rice, provided

it was seeded deeper than 1 inch. Even if rice

is seeded 1 inch deep, seedling growth is inliibited and stands are reduced by CIPC if a

flood is applied to the field 1 to 7 days after

treatment. Usually rice may be flooded 10

days after spraying CIPC without injury.

SPRAY VOLUME.—Rice was sprayed with

CIPC at 6, 8, 10, and 12 pounds per acre as an

early postemergence treatment in 1958 and

1959 in water-spray volumes of 5, 10, 20, and

40 gallons per acre. These treatments were

made with ground equipment. Barnyardgrass

had 1 and 2 leaves. In 1958 CIPC applied in

40 gallons per acre controlled barnyardgrass
WEEDS AND THEIR CONTROL IN RICE PRODUCTION 23

better than applications in 5 and 10 gallons, but

in 1959 there was little difference among

volumes (table 16). Yields were generally

greatest on plots where barnyardgrass was controlled best.

The results of experiments and general field

observations indicate that, if spray coverage

is uniform, CIPC may be applied with ground

or aerial equipment early postemergence in a

water-spray volume of 5 to 40 gallons per acre

TABLE 16.—Effect of volume of CIPC spray on control of barnyardgrass and yield of rice Stxdtgart, Ark., 1958-59

[CIPC applied at early postemergence. Values are averages from plots treated with 6, 8 , 10, and 12 pounds per acre]

Control of barnyardgrass Yield of rice, per acre

Volume of spray per acre

1958 1959 Average 1958 1959 Average

5 gallons

10 gallons

20 gallons

40 gallons

Percent

44

42

48

54

Percent

68

62

75

65

Percent

56

52

62

60

Pounds

2,300

2,330

2,590

2,800

Pounds

4,150

4,140

4,110

4,100

Pounds

3,220

3,240

3,350

3,450

L.S.D. at 5-percent level 8 (') 340 (')

1 No significant difference.

with satisfactory control of barnyardgrass and

with little injury to rice. Spray volumes of

less than 10 gallons per acre tend to produce

spray droplets that drift excessively. Spray

volumes of less than 10 gallons per acre should

be avoided with ground and aerial equipment.

SOIL TYPE.—Control of barnyardgrass with

CIPC was compared on Crowley silt loam and

Sharkey clay (table 17). CIPC generally controlled barnyardgrass more effectively on

Crowley silt loam than on Sharkey clay, and

rice yields were greater. These data and other

research suggest that higher rates of CIPC are

required on clay than on loam soils for equivalent weed control. Even though yield differences between untreated and treated plots were

less on Sharkey clay than on Crowley silt loam,

treated plots yielded much more than untreated

ones on both soil types.

PaCE VARIETY.—In a greenhouse experiment

in Arkansas, when Arkrose, Bluebonnet 50,

Century Patna 231, Cody, Nato, Toro, and

Zenith were seeded II/2 to 2 inches deep, they

were not injured by CIPC applied early postTABLE 11.—Effect of soil type on CIPC activity in control of barnyardgrass and on yield of rice,

Stuttgart, Ark., 1956-57

[CIPC applied at early postemergence]

Year and soil type

1956:1

Crowley silt loam

Sharkey clay _ _

1957:2 ""

Crowley silt loam

Sharkey clay

Control of

barnyardgrass

on treated

plot

Percent

76

54

82

62

Yield of rice, per acre

Untreated

Pounds

1,660

1,980

2,510

3,500

Values are averages from plots treated with 6 and 8 pounds of CIPC per acre.

' Plots treated with 6 pounds per acre of CIPC only.

Treated

Pounds

3,770

3,560

4,340

4,590

Increase for

treated plot

Percent

128

80

73

31
24 AGR. HANDB. 292, U.S. DEPT. OF AGRICULTURE

emergence. Plants from all of these varieties

planted 1/2 inch deep were inhibited in growth

by CIPC, but varieties Century Patna 231,

Cody, and Nato were inhibited more than the

others.

In greenhouse experiments in Louisiana,

CIPC at 6 pounds per acre injured Nato rice

seeded V2 to li/o inches deep in a silt loam soil.

CIPC did not injure varieties such as Bluebonnet 50, Sunbonnet, and Zenith seeded % to

11/0 inches deep, but it injured these varieties

when seeded shallower than three-quarter inch

(8). This difference was due to the development of the first node near the soil surface.

Nato produced the first node near the soil surface at all seeding depths, but the other varieties produced the first node deeper as the seeds

were placed deeper. Roots were produced at

the first node. If the roots developed in the

surface soil where CIPC was present, the rice

was injured.

When Bluebonnet 50, Caloro, Century Patna

231, Gulfrose. Nato, and Zenith were seeded in

the field 1 or 2 inches deep and sprayed early

postemergence with 6 and 12 pounds per acre of

CIPC, they were not injured by the herbicide.

Commercially grown varieties of rice usually

were not injured by CIPC if they were seeded

1 inch or deeper.

Controlling Broadleaf Weeds With

Phenoxy Herbicides

Most broadleaf and aquatic weeds and many

sedges that infest rice are controlled by postemergence treatments with phenoxy herbicides,

but grass weeds and some sedges are not controlled. Phenoxy herbicides used for controlling broadleaf weeds in rice include 2,4-D,

MCPA, 2,4, 5-T, and silvex. These herbicides

are applied either as amine or low-volatile ester

formulations at rates of V2 to 2 pounds per

acre acid equivalent. The rate depends on the

weed species and stage of growth of the rice.

MODE OF ACTION.—The mode of action of

phenoxy herbicides in plants has been frequently discussed (20,56). Phenoxy herbicides

are absorbed by both roots and leaves. They

are translocated from the site of absorption to

the site of action. The movement of phenoxy

herbicides, therefore, may be upward into

young leaves, downward into young roots, or to

rapidly growing parts anywhere in the plant.

Kind of plant, growth stage of the plant, rate

of plant growth, temperature, humidity, soil

moisture, soil-nutrient level, soil type, and possibly other conditions affect the rate of absorption and translocation of phenoxy herbicides in

plants.

Phenoxy herbicides are known to affect

many interacting plant processes and cause

death of the plant. Effective herbicidal action

involves penetration of plant membranes, absorption and accumulation by cells, translocation through tissues and by the vascular system, and finally a toxic action usually involving

the living protoplasm (20). Experiments have

shown that the herbicidal action of phenoxy

herbicides may be inñuenced by each of these

physiological and biochemical processes and

that the herbicides may in turn affect the

processes.

GROWTH STAGE OF RICE AND TYPE AND RATE

OF HERBICIDE.—The response of rice plants to

phenoxy herbicides is greatly influenced by

their stage of growth. Very young rice (from

emergence to 3 weeks after emergence) is injured severely or even killed by 2,4-D, 2,4,5-T,

MCPA, and silvex at rates required to effectively control weeds. Growth of rice in the

early-tillering, late-jointing, booting, or heading stages may be seriously inhibited. Rice in

the late-tillering stage is usually uninjured by

phenoxy herbicides. This "tolerant" stage

usually occurs 7 to 9 weeks after emergence for

early (Nato, Northrose, Nova) and midseason

(Bluebonnet 50) varieties. For very early

varieties (Belle Patna, Vegold), the "tolerant"

stage occurs 5 to 6 weeks after emergence.

Yields of rice are greatly reduced and vegetative abnormalities are produced when 2,4-D,

MCPA, and other phenoxy herbicides are applied at the early-tillering, jointing, or booting

stages of growth. In a 6-year investigation,

2,4-D applied at % and 2 pounds per acre to

rice in the early-tillering and booting stages of

growth reduced rice yields 17 and 16 percent,

respectively (table 18). Yields were not significantly affected when rice was treated in the

late-tillering and jointing stages of growth.

Rice responds differently to postemergence

applications of the phenoxy herbicides. MCPA

is less toxic to rice than 2,4-D, especially when

applied during the early stages of growth (105,

106). During the 4- to 8-week period of rice

development, 2,4,5-T and silvex are less toxic

to rice than 2,4-D or MCPA. Silvex and 2,4,5-T

did not reduce yields when applied at early- and

late-tillering and jointing stages of growth, but

they did reduce yields when applied at the

booting stage (table 18). All these herbicides

may reduce yields severely when they are applied during the booting and heading stages.

Sometimes 2,4,5-T, MCPA, and silvex affect

rice yields less than 2,4-D even when they are

applied during the "tolerant" stage. Generally,

rice is injured most severely by 2,4-D, followed
WEEDS AND THEIR CONTROL IN RICE PRODUCTION 25

TABLE 18.—Effect of time of application of phenoxy herbicides on yield of rice, Stuttgart Ark

1955-61

IValues are averages from plots treated with 3^ and 2 pounds; of phenoxy herbicides per acre]

Change in yield, per acreHerbicide and stage of rice'

1955 1956 1957 1958 1959 1961 Average

2,4-D:

Early tillering

Late tillering

Percent

-13

+ 1

-10

-14

Percent

-20

-6

-9

-18

Percent

-24

+22

+ 12

-21

Percent

-16

+ 5

-2

-19

Percent

-4

+8

-8

-9

Percent

-27

-4

Percent

-17

+4

Jointing -3

Booting - _ -17 -16

L.S.D. at 5-percent level 8 8 21 10 12 8 11

2,4,5-T:

Early tillering -7

-5

+3

-21

+2

+ 13

+2

-14

+7

+4

-4

-14

-1

-2

0

Late tillering +2

Jointing 0

Booting -29 -20

L.S.D. at 5-percent level 21 10 12 8 13

MCPA:

Early tillering -20

-2

+ 1

-7

-7

-3

+3

-19

-14

Late tillering -2

Jointing +2

-13

L.S.D. at 5-percent level 21 10 15

Silvex:

+2

-10

0

-18

-2

-2

-2

-4

+ 11

+2

+6

-11

+4

Late tillering -3

Jointing +1

-11

21 10 12 14

1 2,4-D, 2,4,5-T, and MCPA formulated as amine salts. Silvex formulated as the propylene glycol butyl ether ester. Herbicides apphed about 5, 8, 11, and 14 weeks after rice emergence for early-tillering, late-tillering, jointing, and bootmg stages,

respectively. v ij f

= Yield expressed as percentage of reduction Í-) or increase ( + ) as compared with untreated weed-free check, yields lor

the untreated check were 3,710, 3,500, 4,430, 3,820, 4,300, and 5,700 pounds per acre for 1955-61. The 6-year average yieia

for the untreated check was 4,240.
26 AGR. HANDB. 292, U.S. DEPT. OF AGRICULTURE

by MCPA, silvex, and 2,4,5-T in decreasing

order. The difference in tolerance of rice to

2,4-D and MCPA is not significant except in

the early stages of growth. The difference in

tolerance of rice to 2,4,5-T and silvex is not

significant. However, the tolerance of rice to

2,4-D and MCPA as compared to 2,4,5-T and

silvex is significant.

Phenoxy herbicides may cause vegetative

malformations in rice. Rice treated with 2,4-D

at the early-tillering stage grew tubular leaves

and malformed panicles (fig. 4) ; but that

treated with MCPA, 2,4,5-T, and silvex at the

same stage was not damaged. All these herbicides applied at any stage may injure roots

moderately to severely. The phenoxy herbicides may cause the rice plants to turn dark

green soon after spraying when applied to

early-tillering rice, or cause chlorosis or yellowing when applied to booting or heading rice.

They may also afliect changes in the leaf position from upward to outward or downward

when applied to rice in the booting or heading

stages.

Rice height was reduced significantly by

2,4-D applied at the early-tillering stage (table

19). It was significantly increased by 2,4,5-T

and silvex applied at the jointing and booting

stage and by MCPA applied at the booting

stage. Silvex, 2,4,5-T, and 2,4-D applied to

booting rice reduced the bushel weight

(table 19).

TABLE 19.—Effect of time of application of

phenoxy herbicides on height and btishel

weight of rice, Stuttgart, Ark., 1957-59

[Values are averages from plots treated with 54 and

2 pounds of phenoxy herbicides per acre]

Change in height when rice was

treated at^—

Herbicide'

Early

tillering

Late

tillering Jointing Booting

2,4-D

Percent

-3

0

-2

+2

Percent

+1

+1

-1

0

Percent

+2

+5

+2

+4

Percent

+2

2,4,5-T -_ _-_ +12

MCPA

Silvex _ _ _

+5

+10

L.S.D. at 5- percent level 3 3 3 3

Change in bushel weight'

2.4-D 0

+0.6

+ .4

-0.2

+ .4

+ .2

+1.0

+ .2

0

-0.9

2,4,5-T -1.7

Silvex -1.1

L.S.D. at 5 -percent level .9 .9 .9 .9

FiGiiRE 4.—Left, Two untreated plants; right, rice with

malformed leaves and panicles, caused by injury from

2,4-D applied at the early-tillering stage.

1 2,4-D, 2,4,5-T, and MCPA applied as the amine formulations. Silvex applied as the propylene glycol butyl ether

ester.

- Expressed as percentage of reduction ( — ) or increase

( + ) as compared with untreated weed-free check. Values

are averages of 3 years of data, 1957-1959. Average height

for untreated check was 44.8 inches for 2,4-D, 2,4,5-T, and

silvex comparisons and 44.4 inches for MCPA comparisons.

'Expressed as percentage of reduction ( —) or increase

(+ ) as compared with untreated weed-free check. Values

are averages of 1 year of data, 1959. Average bushel weight

for untreated check was 46.2 pounds.
WEEDS AND THEIR CONTROL IN RICE PRODUCTION 27

Response of rice to phenoxy herbicides is

affected by rate of application. Injury to rice

by phenoxy herbicides applied at other than the

"tolerant" late-tillering stage increased as the

rate of herbicide increased from % to 2 pounds

per acre. A rate of 2 pounds per acre of

phenoxy herbicides applied at the late-tillering

stage injured rice only slightly more than

three-quarter pound.

WEED RESPONSE TO PHENOXY HERBICIDES.—

Weeds respond differently to 2,4-0, MCPA

2,4,5-T, and silvex. For example, se'sbania is

very susceptible to 2,4-D and 2,4,5-T (fig. 5),

but curly indigo is somewhat resistant to 2,4-D

FIGURE 5.—Control of sesbania with phenoxy herbicides in rice: Left, Unsprayed plot; right, plot sprayed

2,4-D, 2,4,5-T, or silvex.
28 AGR. HANDB. 292, U.S. DEPT. OF AGRICULTURE

and susceptible to 2,4,5-T (table 20). Ducksalad, however, is more susceptible to 2,4-D

than to 2,4,5-T (table 21). When several species of weeds varying in susceptibility to a

herbicide are present in a ricefield, mixtures

of phenoxy herbicides may be used effectively

(table 20). Mixtures of 2,4-D and 2,4,5-T are

often more effective than either herbicide used

alone.

TABLE 20.—Effect of 2,U-D and 2,U,5-T on sesbania and curly indigo, Kelso, Ark., 1960

and 1962

Control of—

go

Herbicide'

Sesbania Curly ind

1960 1962

Average 1960 1962

Average

2,4-D

2,4,5-T

2,4-D plus

2,4,5-T

Percent

95

100

100

Percent

98

95

Percent

96

98

Percent

25

75

100

Percent

30

95

Percent

28

85

' Applied postemergence as amine salts: 2,4-D and 2,4,5-T

applied at 1 pound per acre; Ji pound each of 2,4-D and

2,4,5-T applied in the mixture.

TABLE 21.—Effect of 2,^-D and 2,A,5-T at two

rates on diicksalad, Stuttgart, Ark., 1958-60

Herbicide and

Control of ducksalad

rate per acre'

1958 1959 1960 Average

2,4-D:

1 pound

2 pounds

Percent

80

83

13

47

Percent

100

100

25

75

Percent

"so'

"30 "

Percent

90

88

2,4,5-T:

1 pound - -.

2 pounds

19

51

Applied postemergence as amine salts.

Weeds are usually most susceptible to phenoxy herbicides when they are young, vegetative, and growing rapidly. Because rice is

generally very susceptible to phenoxy herbicides until it is in the late-tillering stage, or

7 weeks old for many varieties, weeds in rice

cannot be treated until they are somewhat

larger than desired for maximum effective control. Sesbania and curly indigo may range

from 2 to 6 feet tall at treatment. Because the

weeds are large, the rate of herbicide required

to kill them must be increased. Broadleaf

weeds, such as sesbania, curly indigo, and ducksalad, usually require rates of 1 to 2 pounds

per acre of herbicide to kill them at this stage

of growth.

In southern rice-growing areas aquatic

weeds, such as ducksalad, waterhyssop, and

redstem, may become a serious problem before

rice reaches the "tolerant" stage. To control

these weeds, 2,4,5-T or silvex can be applied

safely when the rice is in the early-tillering

stage, or 4 to 6 weeks old. At this stage, silvex

and 2,4,5-T should not be applied at more than

1 pound per acre and 2,4-D should not be applied at all. At rates of 1/4, to 1 pound per acre,

2,4,5-T and silvex usually will not control ducksalad completely. Where there is a severe infestation, a second treatment with 2,4-D at 1

pound per acre may be required when the rice

reaches the "tolerant" stage of growth. In

California, MCPA at 1/2 to % pound per acre

can be applied to rice 6 to 7 weeks old without

injuring it. These rates control many easy-tokill weeds, such as redstem, waterhyssop, and

waterplantain.

HERBICIDE FORMULATION.—MCPA, silvex,

2,4-D, and 2,4,5-T are applied as either amine

salt or low-volatile ester formulations. The

amine salt and low-volatile ester formulations

of 2,4-D and 2,4,5-T are very similar in their

effects on rice. Sodium, potassium, and lithium

salts of the phenoxy herbicides are available

but are usually less effective on weeds than

amine salt or ester formulations. Rice is most

"tolerant" to all formulations of phenoxy herbicides during the late-tillering stage of growth.

However, at "susceptible" stages of growth,

esters are more toxic to rice than amine salt

formulations.

Ester formulations of the phenoxy herbicides are usually more effective in controlling

most weeds than amine salt formulations.

Normally, lower rates are required for the ester

than for the amine salt formulations. Under

most growing conditions, about V2 pound per

acre of ester formulation is equivalent to 1

pound of amine salt (on an acid-equivalent

basis).

Amine salts of 2,4-D and 2,4,5-T formulated

as water-in-oil or invert emulsions are being

developed for controlling broadleaf and sedge

weeds in rice. These formulations are more
WEEDS AND THEIR CONTROL IN RICE PRODUCTION 29

active on weeds and drift less than regular

amine formulations (71). Special equipment,

however, is required for their application to

ricefields. Separate tanks, pumps, and booms

are used for the oil (herbicide concentrate) and

water phases of the spray solution. Mixing and

dispersing of the spray material take place in

a specially designed nozzle where the oil and

water phases converge. The herbicide concentrate contains agents that promote a "flash inversion" process when mixed with water. This

process can be defined as an instant structureproducing arrangement of oil and water particles. The resulting spray solution is a highly

viscous emulsion having a consistency similar

to mayonnaise.

In experiments in Texas (71), invert emulsions sprayed with aerial equipment had only

one-tenth percent of the spray volume composed of droplets smaller than 200 microns.

In comparison, regular, or oil-in-water, emulsions had 30 percent of the spray volume composed of droplets smaller than 2Ó0 microns. In

other experiments in Texas, invert emulsions

sprayed with aerial equipment had less than 1

percent of the spray volume deposited beyond

100 feet downwind from the treated area compared with 18 percent for regular emulsion

sprays.

In experiments in Arkansas, invert emulsions

of 2,4-D and 2,4,5-T at V2 to 1 pound per acre

applied by aerial equipment controlled weeds

effectively without damaging rice seriously.

Complete spray coverage was essential for control of ricefield weeds, such as ducksalad, redstem, waterhyssop, sesbania, and curly indigo.

A herbicide-water spray volume of 4 to 8 gallons per acre gave uniform coverage of weeds

and minimum drift of spray droplets. Spray

droplets of invert emulsions should be small

enough to completely cover the weeds but large

enough to resist drift. Droplets that range

from 200 to 1,000 microns in diameter generally meet these requirements. Invert emulsion

formulations of 2,4-D and 2,4,5-T at V2 to 1

pound per acre caused brown spots on the rice

leaves everywhere the spray droplets adhered

to the leaf. The rice, however, outgrew the

damage within 1 to 2 weeks after the spray

treatment.

Granular formulations of 2,4-D and other

phenoxy herbicides do not control ricefield

weeds satisfactorily.

RICE VARIETY.—Commercially grown varieties of rice, such as Arkrose, Belle Patna, Bluebonnet 50, Caloro, Century Patna 231, Improved Bluebonnet, Nato, Nova. Vegold, and

Zenith, respond similarly to phenoxy herbicides provided they are treated at comparable

rates of application and stages of development.

All these varieties are most "tolerant" to phenoxy herbicides during the late-tillering stage.

The time required for rice to reach the latetillering stage varies with variety, time of seeding, soil moisture, soil and atmosphere temperatures, latitude, light intensity, day length,

and soil fertility. Early and midseason varieties reach the late-tillering stage about 7 to 9

weeks after emergence, at which time they may

be sprayed safely with phenoxy herbicides.

Very early-maturing varieties, such as Belle

Patna and Vegold, reach the late-tillering stage

5 to 6 weeks after seedling emergence, and they

should be sprayed at this time. Midseason

varieties, such as Arkrose and Bluebonnet 50,

remain in the late-tillering stage longer than

early varieties, such as Century Patna 231 and

Nato. Midseason varieties, therefore, may be

sprayed over a longer period than early varieties. For example. Nato may be sprayed safely

during a 2-week period, 7 to 9 weeks after

emergence but Bluebonnet 50 may be sprayed

during a 3-week period, 7 to 10 weeks after

emergence. Seasonal environment and time of

seeding affect the length of the "tolei-ant"

spraying period.

METHOD OF SEEDING AND WATER MANAGEMENT.—When phenoxy herbicides are applied

at 1/2 to IV2 pounds per acre during the "tolerant" stage, method of seeding and water

management do not usually influence the response of rice to these herbicides. Seeding

method and water management may significantly affect the activity of phenoxy herbicides

on rice when the herbicides are applied in the

"susceptible" stages, especially rice 3 to 6

weeks old. The stage of rice development at

the time of applying phenoxy herbicides, however, is much more important than seeding

method or water management.

Water management may affect the response

of weeds to phenoxy herbicides. If water covers low-growing aquatic weeds, such as ducksalad, redstem, and waterhyssop, at spraying

time, the weeds may not be controlled because

the herbicide does not contact the plants. If

weeds are not growing rapidly because of dry

soil or other reasons, they may not be controlled satisfactorily. Dry soil may be caused

by draining the water from the field 7 to 14

days in advance of spraying. The water should

be drained from the field only a few days betöre

spraying (3 to 6 days) to insure enough soil

moisture. Flooding the field too soon alter

spraying may wash off the phenoxy herbicide

from the weed plants and reduce its activity.

Flooding may begin 12 hours after spraying,

however, without affecting this activity.
30 AGR. HANDB. 292, U.S. DEPT. OF AGRICULTURE

FERTILIZER MANAGEMENT.—Sometimes nitrogen applied to rice before phenoxy herbicide

treatment increases the activity of 2,4-D on

rice. However, in field experiments in 1958 and

1960 in Arkansas, nitrogen applied to rice 14

days before or after 2,4-D treatment did not

affect the activity of 2,4-D on rice. And in

experiments in 1961 and 1962, the interacting

effects of nitrogen and 2,4-D—the nitrogen

was applied 14 days before 2,4-D treatment—

reduced yields 11 and 9 percent, respectively.

Yields from weed-free untreated check plots

were 4,610 and 6,110 pounds per acre for 1961

and 1962, respectively. Nitrogen stimulated

growth of rice 4 to 5 days after application.

By the time 2,4-D was applied 14 days after

the nitrogen application, rice was green and

growing rapidly. After treatment with 2,4-D,

rice exhibited symptoms of injury on the leaves.

Rice treated with nitrogen 5 days before treatment with 2,4-D was not injured. This information suggests that nitrogen should be applied so as not to stimulate rapid rice growth

just before phenoxy herbicide applications.

Nitrogen also stimulates the growth of

weeds. Rapidly growing weeds are more susceptible to phenoxy herbicides than are slowly

growing weeds. Nitrogen, therefore, applied

before phenoxy herbicide treatment may increase the activity of these herbicides on weeds.

Because nitrogen applied too far ahead of

phenoxy herbicide treatments may increase

their activity on rice, nitrogen should be applied 1 to 5 days before or after phenoxy herbicides even though the weeds may be less susceptible to the herbicides. If soil moisture is

adequate, the weeds are usually growing

rapidly enough to respond to phenoxy herbicides.

WEATHER.—Rice treated under greenhouse

conditions with 2,4-D, MCPA, and 2,4,5-T was

injured more when subjected for 3 days (2

days before and 1 day after herbicide treatment) to 97° F. than when subjected to 62° to

72° (52). Rice 2 to 8 weeks old exposed to a

temperature of 97° was injured severely by

phenoxy herbicides, but as the age of rice increased from 2 weeks, injury was less. Under

high temperatures, rice was injured most by

2,4-D, followed by MCPA and 2,4,5-T in decreasing order.

The effect of temperature in increasing the

activity of phenoxy herbicides on rice is greatly

influenced by the rate of plant growth within

stages of growth of rice. The stage of development and rate of growth of the rice plant at

time of treatment is as important as, or more

important than, temperature per se before, at,

or after treatment.

Weeds respond best to phenoxy herbicides

when temperatures are moderate (from 70° to

85° F.). Low temperatures (50° to 65°) during the week before spraying often slow weed

growth and reduce herbicidal activity.

Rainfall immediately after postemergence

foliage application of phenoxy herbicides may

reduce their effectiveness on weeds. If rain occurs 6 to 12 hours after treatment, the effectiveness of the phenoxy herbicides is usually

not reduced. Esters resist washing from the

plant more effectively than amine salt formulations.

Moderate or high humidity (60 to 90 percent relative humidity) increases the effectiveness of phenoxy herbicides. The humidity is

usually moderate to high in ricegrowing areas.

Rice is often sprayed during the early morning

or late afternoon when humidity is highest.

Rice is sometimes sprayed with helicopters or

fixed-wing airplanes at night, when humidity

is very high and the wind is not blowing more

than 5 miles per hour.

SPRAY VOLUME AND METHOD.—Phenoxy

herbicides are applied with low-gallonage

sprayers attached to ground or aerial equipment. A volume of 5 to 15 gallons is satisfactory with ground equipment, and from 1 to 10

gallons per acre is required for aerial spraying.

Regardless of method of application the spray

should be applied uniformly to the field.

IMPACT OF NEW AND IMPROVED METHODS OF CHEMICAL

WEED CONTROL ON RICE PRODUCTION

The development of efficient and economical

methods of full-season control of broadleaf and

grass weeds in rice will have a revolutionary

impact on rice production (79). Chemical

methods of weed control are already having an

important impact on levee construction, the

kind and thoroughness of seedbed preparation,

method of seeding, water management, type of

irrigation, selection of varieties, fertilizer management, pest and insect control, and rotations.
WEEDS AND THEIR CONTROL IN RICE PRODUCTION 31

Impact on Seeding Methods and

Water Management

Ricegrowers in southern rice-producing areas

are switching from water seeding to dry

or drill seeding of rice because effective and

economical herbicides are now available to control grass weeds. The trend in Louisiana had

been to water seed rice to control grass weeds.

Availability of effective herbicides is changing

this trend.

In California deep water is used primarily to

control barnyardgrass. The use of herbicides

rather than deep water to control weeds is having an important impact on water conservation

and rice culture in California.

Algae are a serious problem in water-seeded

rice on heavy clay soils in southern rice-producing areas. The only method of controlling algal

growth is by water management or draining to

desiccate, or dry out, algae. Other weeds, including barnyardgrass, germinate and emerge

while the field is drained for control of algae.

The development of selective herbicides to effectively control algae will eliminate the need for

draining, which will therefore reduce problems

with grass weeds.

Dry-planted rice may be flooded immediately

after rice emergence to control young barnyardgrass or other grass weeds. When temperatures are warm (80° to 95° F.), early flooding

may effectively control grass weeds; but when

cool temperatures (60° to 75°) prevail, control

is often ineffective. Moreover, early flooding

may stimulate stem elongation and weaken

young rice seedlings. Effective herbicides for

controlling grass weeds should eliminate the

necessity for early flooding. This practice will

then permit better establishment of the rice

seedlings before flooding.

Impact on Selection of Varieties

Early and midseason varieties of rice are

widely used for commercial production. These

varieties usually require 130 to 150 days from

seeding to maturity. Most varieties of barnyardgrass produce seed 45 to 70 days after

rice has been seeded. Once barnyardgrass

heads, it is not nearly so competitive with rice

as before it heads. If nitrogen is managed

properly, rice requiring 130 to 150 days to

mature may recover considerably from early

grass competition after the barnyardgrass

matures. Moreover, barnyardgrass is not

nearly so competitive with midseason varieties

as it is with very early varieties.

Very early varieties of rice, such as Belle

Patna and Vegold, are available for commercial production. These varieties mature in approximately 100 days from seeding. They do

not have an opportunity to recover from competition of barnyardgrass, which may mature

only shortly before the rice. Very early varieties should be planted only where grass weeds

are to be controlled. New, effective, and

economical grass-weed herbicides will be important in the profitable production of these

new very early varieties of rice.

Impact on Fertilizer Management

Many of the older rice-producing areas in the

South are low in phosphate and, therefore, require supplemental applications of commercial

formulations of phosphate. Where phosphate

is required, it is usually applied to a crop in

the rotation other than rice because phosphate

applied before seeding rice stimulates growth

of grass weeds, especially barnyardgrass. For

example, in a rice-soybean rotation, phosphate

is generally applied to the soybean crop. Conceivably, this practice may lead to a deficiency

of phosphate when the young rice plants need

it most. An inadequate supply of phosphate

during the early vegetative stages of rice

development may retard rice growth and reduce yields. Herbicides effective for controlling

grass weeds will allow application of phosphate

before seeding rice and result in better rice

yields.

Where grass weeds infest ricefields, nitrogen

applications must be delayed until the grass

heads. Mature grass plants utilize less nitrogen

than young vegetative ones. Nitrogen applied

when grass weeds are mature, therefore, is

more available to the rice than to the grass.

Presently (1964) the time and amount of nitrogen applied to rice depend on whether grass

weeds are absent or present. Where grass

weeds are absent, nitrogen can be applied 10

to 15 days after rice emergence; but where

they are present, nitrogen is applied only after

the grass heads out, or 50 to 60 days after rice

emergence.

Impact on Insects

In an investigation in Arkansas, rice stink

bug infestations were directly related to grassweed infestations, especially barnyardgrass

(68). Fields free of grass weeds have very

low populations of stink bugs throughout the

season, including the period that rice is most

susceptible to damage. Conversely, fie ds wim

heavy infestations of grass weeds develop peaK

populations about the time rice is most suscept-
32 AGR. HANDB. 292, U.S. DEPT. OF AGRICULTURE

ible to damage. Control of grass weeds in ricenelds with herbicides, therefore, results in a

sharp reduction in stink bug infestations.

Rolston ' found that seed treatment with

aldrin was ineffective in controlling rice water

weevils where infestations of barnyardgrass

were heavy, but controlled them where barnyardgrass was controlled with herbicides. Such

information suggests that rice water weevils

are controlled by a seed treatment with aldrin

only where barnyardgrass is absent or controlled. Treatment of rice seed with aldrin to

control rice water weevils is commonly practiced by commercial rice growers.

EQUIPMENT FOR WEED CONTROL

Ground equipment (hand and tractor sprayers) and aerial equipment (fixed-wing and helicopter (figs. 6 and 7) sprayers) are used for

applying herbicides to rice. Aerial equipment

is used more commonly than ground equipment.

Aerial equipment has an advantage over gi'ound

equipment because timely and quick applications can be made even though the soil may be

too wet to support a sprayer. In addition,

levees present a problem with ground equipment.

' Private communication from L. H. Rolston, Associate Professor of Entomology, University of Arkansas,

Fayetteville, 1963.

Hand Sprayers

Several types of hand sprayers are available

for use in rice; they include regular and constant-pressure knapsack sprayers. If uniform

and accurate herbicide applications are required, the constant-pressure knapsack sprayer

is desirable. This sprayer consists of two tanks,

one for the spray solution and the other for

compressed air or other compressed gases. The

tanks are connected with a hose through an air

pressure regulator, which keeps the gas pressure constant in the liquid tank. This system

may be calibrated for applying precise rates

of herbicides.

FIGURE 6.—Application of 2,4-D to rice for control oof broadleaf weeds with a fixed-wing- airplane sprayer.
WEEDS AND THEIR CONTROL IN RICE PRODUCTION 33

rí5«ÍSií.«aWa*íSaKÍ?¿5í!e

FIGURE 7.—Application of 2,4-D to rice for control of broadleaf weeds with a helicopter sprayer.

Tractor Sprayers

Tractor-mounted sprayers consist of a powertakeoff-driven pump, tank or tanks, solution

delivery hose, pressure regulator, pressure

gage, nozzles, strainers, and booms. The boomtype sprayer is most commonly used, but boomless sprayers are used sometimes, especially

over rough terrain and where even distribution

of spray is not essential.

Herbicides are applied to rice with ground

equipment at spray volumes of 5 to 20 gallons

per acre.

Tanks

Tanks are available in mild steel (such as oil

drums), stainless steel, aluminum, and plastic

reinforced with fiber glass. Much of the trouble

with clogged nozzles in oil-drum tanks is caused

by rust and scale that accumulate between

spraying seasons. The other three materials

are more expensive than mild steel, but they

withstand the corrosive action of most herbicides. Nozzle stoppage is much less when tanks

are constructed of corrosive-resistant materials.

Pumps

Several types of pumps, including centrifugal, piston, gear, roller, and rubber impeller,

are available for spraying herbicides. They are

I'ated in gallons-per-minute discharge at specific speeds. The capacity of the pump should

be about twice that of the total nozzle delivery

rate to provide adequate flow through the bypass line for hydraulic agitation in the tank.

Hoses and Connections

The hose should be resistant to sunlight, oil,

and chemicals and should withstand general

use. A hose made of base rubber combmed

with tough rayon and nylon cord gives good

service. Hose connections should be made of

corrosive-resistant materials and should have

openings large enough to avoid restrictions m

the lines.
34 AGR. HANDB. 292, U.S. DEFT, OF AGRICULTURE

Pressure Regulators

Two types of bypass pressure regulators are

generally available for pressure regulation for

low-volume, low-pressure spraying. One type

consists of a spring over a ball and seat; the

other consists of a spring, diaphragm, plunger,

and seat. Both types have an adjusting screw

to regulate pressure.

Sometimes a pressure-reducing regulator is

used in conjunction with the bypass pressure

regulator. The bypass valve may be set at

10 to 15 pounds above the desired pressure at

the nozzle tips. The reducing regulator may

then be set to maintain a uniform pressure on

the nozzle tips even though the pump may cause

some fluctuation in the delivery pressure at

the bypass valve.

Pressure Gages

The pressure gage must be accurate. It

should be placed in the hose between the pressure regulator and the delivery nozzles. Gages

with a range of 0 to 100 pounds per square inch

are satisfactory. The scale should be in 1- or

2-pound divisions to facilitate easy and accurate calibration of the sprayer.

Nozzles

Broadcast booms used for spraying rice

should usually be fitted with fan-type nozzle

tips that produce a heavy center spray. Size

of the nozzle is determined by the particular

spraying job. The manufacturer's guide may

be consulted for information.

Booms

Broadcast spray booms are classed as wet or

dry. A pipe or metal tube transports the liquid

in the wet boom. Usually a pipe coupling or

eyelet fitting is welded or placed over small

holes spaced 18 to 20 inches apart in the pipe.

The materials used for making the boom should

be resistant to corrosion to prevent nozzle

stoppage.

In the dry boom the supporting member does

not carry the liquid. The liquid is transported

by hoses and fittings, which consist of pipe tees

bolted to the supporting frame. This type of

boom is very satisfactory because corrosion is

minor and the boom can be straightened after

accidental bending without leakage.

Strainers

Line and nozzle-tip strainers should be used

in the sprayer to remove solid particles that

may clog nozzle tips. Usually 50- or 100-mesh

screens are satisfactory. All strainers should

be removed, cleaned, and inspected for holes

every few days.

Fixed-Wing Airplane Sprayers

Most airplane sprayers are equipped with

booms and nozzles that are similar to those on

tractor sprayers. Other distribution systems

include rotating brushes, disks, hollow propellers, and the venturi type, which may be a

single large unit under the fuselage or several

small units mounted under each wing. The

boom-type distribution system is usually more

desirable for spraying herbicides.

Phenoxy herbicides are applied to rice at

spray volumes of 1 to 10 gallons per acre to

control broadleaf weeds. Propanil and CIPC

used to control grass weeds are applied at

volumes of 10 gallons per acre.

The same type of pumps used with tractors

are used with airplanes, but the centrifugal

pump is most common. The pump is mounted

outside the fuselage and driven by a small

propeller. The size of the propeller may be

changed for the desired volume of spray. The

capacity of the pump should be about twice

the nozzle output to allow sufläcient liquid

through the bypass valve for hydraulic agitation.

Tanks are usually made of corrosive-resistant materials, such as aluminum or fiber glass,

and they carry 90 to 250 gallons of spray liquid.

Pressure regulators, pressure gages, hoses,

and strainers used for aerial spraying are similar to those used on tractors.

Booms are usually made of corrosive-resistant materials, such as aluminum. To minimize

drift of spray, the boom should be placed as

far below the wing as practical, which is

usually about 1 foot; and it should extend to

within about 2 feet of the wingtip. If the boom

extends to the wingtip, the spray may be

whirled upward in the wingtip vortices to cause

excessive spray drift.

Nozzles for fixed-wing airplane sprayers are

made of corrosive-resistant material, such as

aluminum, brass, or nylon. They are equipped

with quick-cutoff diaphragm, screen, and jet.

Spray droplet size may be greatly affected by

the angle at which the nozzles discharge into

the airstream. Smaller droplets occur when the

nozzles are directed against, or across, the airstream than when they are directed with it.

Droplet size is also affected by pump pressure

and nozzle-orifice diameter. Most ricegrowing

States have regulations that specify the maximum operating pressure for aerial spraying

of phenoxy herbicides; this usually must not
WEEDS AND THEIR CONTROL IN RICE PRODUCTION 35

exceed 20 to 45 pounds per square inch. A

compromise must be made between small droplets, which give thorough coverage but have a

tendency to drift, and large ones, which settle

fast but do not give adequate coverage. Sprays

usually give adequate weed control if droplets

range from 50 to 300 microns in diameter.

Spray pattern or distribution is important.

Proper placement and spacing of nozzles along

the boom helps to distribute the spray evenly.

Usually the spray pattern will be improved if

more nozzles are placed on the right side of the

plane than on the left. The air is swirled from

right to left by the counter clockwise rotation

of the propeller (facing the propeller). Spraying the proper swath width also improves spray

distribution. The wing span of the airplane

governs the swath width. The width of the

swath should be about equal to—but should

never exceed—the wing span of the plane.

Proper flying height improves spray pattern

and reduces spray drift. Spray distribution is

best when fixed-wing airplanes fly at 10 to 15

feet, but spray drift is less when they fly at 5

to 10 feet. Phenoxy herbicides should be released at the lowest possible height, but propanil may be released at a height that gives best

spray distribution.

Helicopter Sprayers

Helicopters are frequently used to apBlv

herbicides to rice. Some users claim that spray

applications from helicopters provide better

coverage and control of weeds than do those

from fixed-wing planes because the downwash

from the helicopter motors forces the spray

down into the crop. In closely bounded fields a

helicopter can be used advantageously to give

better weed coverage near the edge of the ricefield and to reduce spray drift to nearby susceptible crops. The helicopter may stay within

the ricefield while turning at the ends of the

field. This eliminates flight over nearby susceptible crops, which prevents accidentally contaminating these crops by spray trailing the

aircraft or by leakage of spray.

The boom-type sprayer is used on helicopters.

Pumps, tanks, hoses, pressure regulators, pressure gages, nozzles, booms, and strainers used

on helicopters are similar to those used on

fixed-wing planes.

A helicopter carries about 60 gallons of spray

liquid in two spray tanks; one is located on

each side of the aircraft for balance. The flying

height is usually 2 to 5 feet above the rice. The

swath width should be about equal to the length

of the boom.

CALIBRATION OF TRACTOR AND AERIAL SPRAYERS

Unless the sprayer is calibrated properly, the

crop may be injured by too much herbicide or

the weeds may be controlled poorly by too little

herbicide. The herbicide must be mixed with

water in the right proportion. Proper calibration of the sprayer is very important for good

results with herbicides.

Low-gallonage sprayers are used for spraying herbicides on rice. Volumes of 5 to 20 and

1 to 10 gallons per acre are used for tractor

and aerial sprayers, respectively. A good

method of calibration is to make initial adjustments to suit the machine and job requirements

and then make a trial run to determine the

actual output of the sprayer. The herbicide

spray solution should then be prepared accordingly. The calibration should be repeated frequently to check for nozzle-orifice wear and

other things that may change the spray output.

The nozzle (type, size, etc.) that will give

the desired volume of spray per acre is first

selected from the manufacturer's guide. Then

all nozzles are checked to see if they are discharging evenly. Individual nozzles may be

checked for accuracy of delivery by measuring

the volume of spray from each nozzle in 1

minute. If serious variations exist, the faulty

nozzle should be cleaned or replaced. The speed

of the tractor or aircraft that best fits the

spraying job requirements is then selected.

There are many ways of calibrating a sprayer.

One method of calibrating a tractor sprayer

and one method of calibrating an aerial sprayer

follow.

Tractor Sprayers

(1) Select an area for a test run that is

similar to the field to be sprayed. Measure off

a distance of 660 feet.

(2) Place the sprayer on level ground and

fill the spray tank with water. Make sure it is

full.

(3) Spray the 660-foot test run. Operate the

sprayer at exactly the same pressure and tractor speed that will be used in the field—usually

about 3 or 4 miles per hour.
36 AGR. HANDB. 292, U.S. DEPT. OF AGRICULTURE

(4) Upon reaching the 660-foot mark, stop

spraying. Then measure carefully the number

of quarts needed to refill the tank.

(5) Convert the number of quarts to gallons

of water required to refill the spray tank by

dividing by 4, and then multiply this figure

by 66. Divide the results by the width, in feet,

of the strip sprayed. The answer obtained is

the number of gallons of spray liquid the

sprayer will apply on 1 acre when it is operated

at the same settings.

Example: Suppose the sprayer boom sprayed

a strip 30 feet wide. After the 660-foot strip

is sprayed, 10 quarts is required to refill the

tank. Ten quarts divided by 4 equals 21/2

gallons. Multiply 66 by 21/2, which equals 165.

Then divide 165 by 30 (the width in feet of

the sprayed strip). The answer is 51/2. which

is the gallons of spray liquid applied per acre.

Aerial Sprayers

(1) Measure off a distance of 1 mile (5,280

feet).

(2) Fill the spray tank with water. Make

sure it is full.

(3) When the weather is similar to that

which will prevail while spraying the rice,

spray the 1-mile test run. Operate the sprayer

at exactly the same pressure and airplane speed

(ground speed) that will be used in the field—

usually about 80 to 85 miles per hour for

fixed-wing planes and about 40 miles for helicopters.

(4) Upon reaching the 1-mile mark, cut off

the sprayer. Measure carefully the gallons of

water needed to refill the tank.

(5) Multiply the number of gallons of water

needed to refill the tank by 8i/i. Divide the

results by the width, in feet, of the strip

sprayed. The answer obtained is the gallons of

spray liquid the sprayer will apply on 1 acre

when it is operated at the same settings.

Example: Suppose the strip sprayed is 33

feet wide. After the 1-mile strip is sprayed,

12 gallons is required to refill the tank. Multiply 12 by 814,, which equals 99. Then divide 99

by 33 (the width in feet of the sprayed strip).

The answer is 3, which is the gallons of spray

liquid applied per acre.

Slight pressure adjustments may be required

to obtain the desired liquid output of the

sprayer. Each time the sprayer is readjusted

the output of the sprayer must be checked as

described. It is a good idea to check the spray

distribution pattern on both tractor and aerial

sprayers. This may be done by placing a watersoluble dye in the tank. Place a strip of white

paper on the ground across the swath and

spray and operate the tractor or aerial sprayer

exactly the same as it will be operated in the

field. Slight height, nozzle, and other adjustments may be required to obtain the desired

spray pattern.

Once the sprayer is calibrated accurately,

determine the acres that can be sprayed with

one tankful of spray liquid. This is done by

dividing the capacity of the tank (in gallons)

by the spray applied per acre (in gallons).

Example: Suppose the tank holds 90 gallons

of spray liquid and the sprayer is calibrated to

apply 3 gallons per acre. Divide 90 by 3. The

answer is 30, which is the number of acres one

tankful of spray liquid will cover.

Now determine the amount of commercial

herbicide and water needed to make the desired

spray solution. Suppose you want to kill ducksalad in rice, which requires IV2 pounds per

acre of 2,4,5-T acid equivalent. Multiply 30

by IV2. which equals 45, or the pounds of

2,4,5-T required for each tankful of spray.

Suppose the commercial 2,4,5-T you are using

contains 4 pounds per gallon acid equivalent.

Divide 45 by 4, which equals II14, or the gallons of 2,4,5-T needed for each tankful of

spray. Thoroughly mix the 1114, gallons of

2,4,5-T with sufficient water to fill the tank.

You are now ready to spray.

WEEDS

Accurate weed identification is essential to

a satisfactory weed-control program because

weeds differ in their response to various chemical and cultural methods of control. Only

weeds that cause major losses in rice production are described in this section. However,

others not included are also known to reduce

rice yields. The principal species infesting rice

in the United States are listed, and a description, distribution and habitat, and information

on control are included. When a weed is known

by more than one common name, the most

widely used names are given. Pictures of representative species are also included. The background board in most of the pictures was

marked off in 6-inch squares.
WEEDS AND THEIR CONTROL IN RICE PRODUCTION 37

Arrowhead (f)g. 8)

Sagittaria spp.

OTHER NAMES.—Swamp-potato and arrowheadlily.

PRINCIPAL SPECIES.—Sagittaria montevidensis Cham. & Schlecht., S. latifolia Willd., S.

cuneata Sheldon, and S. gramínea Michx.

DESCRIPTION.—Species of arrowhead are

perennials that reproduce by seed, underground

rhizomes, and tubers. They are rooted aquatics,

usually emersed. The common species have

arrow-shaped leaves, but some species have

linear ones. The normal leaves are all basal

with petioles usually as long as the water is

deep. Plants are normally 1 to 2 feet tall.

DISTRIBUTION.—Arrowheads grow in all riceproducing States, and several species grow in

most States. They grow in shallow water in

irrigation and drainage canals, in ricefields

where stands are thin, and in ricefield bar

ditches.

CONTROL.—Arrowheads may be controlled

by good cultural practices, such as thorough

land preparation, land leveling, and proper construction of levees. A good stand of rice discourages arrowheads.

They may also be controlled in the ricefields

by 2,4-D, 2,4,5-T, silvex, or MCPA at 1/2 to

IV2 pounds per acre. Sometimes only partial

control is obtained at these rates. These herbicides should be applied to rice when it is in the

"tolerant" stage (p. 24). In irrigation canals

or on uncultivated areas these herbicides may

be applied at 4 to 8 pounds per acre, with water

or fuel oil as the carrier.

FIGURE 8.—Arrowhead {Sagittaria montevidensis).
38 AGR. HANDB. 292, U.S. DEPT. OF AGRICULTURE

Barnyardgrass

Echinochloa spp.

PRINCIPAL SPECIES, VARIETIES, AND COMMON

NAMES.—Echinochloa crusgalli (L.) Beauv.

(fig. 9) called watergrass, millet, bluestem, and

baronetgrass; E. colonum (L.) Link called

jungle-rice, little barnyardgrass, and shortmillet; and E. crtispavonis (H.B.K.) Schult,

called gulfcockspur and cattailgrass. There are

many varieties of E. crusgalli, including zelayensis (H.B.K.) Hitchc, longiseta (Trin.) Farw.,

and those commonly known as baronetgrass

and white barnyardgrass.

DESCRIPTION.—Species and varieties of barnyardgrass that infest rice are annuals; they reproduce by seed. Because the species differ

greatly, separate descriptions are given.

Echinochloa crusgalli varies more morphologically than other species do. It is erect to

decumbent and ranges from 3 to 6 feet tall at

maturity. Some varieties of barnyardgrass are

awnless; others have awns—the length varies

with the variety. Varieties differ greatly in

date of maturity, height, and size of stems,

heads, and seeds. (Panicles Of several varieties

of E. crusgalli are shown in figure 10.) Varieties also differ in their ability to emerge under

water. White barnyardgrass, which grows in

FIGURE 9.—Barnyardgrass (Echinochloa crusgalli),

mature plant.

FIGURE 10.—Barnyardgrass panicles, showing head types.
WEEDS AND THEIR CONTROL IN RICE PRODUCTION 39

California, germinates under water; but other

varieties usually will not germinate when seeds

are covered with water.

Echinochloa colonum is prostrate to erect

and ranges from 1 to 2 feet tall at maturity. It

branches more at the base than E. crusgalli and

grows more openly and has smaller culms,

heads, and seeds.

Echinochloa cruspavonis is erect or sometimes

decumbent, and plants are about 3 to 4 feet

tall at maturity. The panicles are very conspicuous because they are large, and the spikelets have long awns.

All species of barnyardgrass tiller abundantly and produce abundant viable seed that

may persist for many years in the soil.

Young barnyardgrass plants often are difficult to distinguish from rice. The collar region

on the leaves may be used to differentiate these

plants. Barnyardgrass has no ligules or auricles; rice has membranous ligules and hairy

auricles (fig. 11).

FIGURE 11.—Collar region of barnyardgrass (left) and

of rice (right). Barnyardgrass has no ligule or

auricle; rice has ligules and hairy auricle.

BiSTRlBvrio-N.—Echinochloa crusgalli is a

troublesome weed in all ricegrowing States

E. colonum and E. cruspavonis grow mostly in

Louisiana and Texas, but E. cruspavonis is not

widespread. All species grow well in rice because water is plentiful. Barnyardgrass grows

in the rice crop, on levees, along irrigation and

drainage canals, on reservoir banks, and in

sloughs and other wet areas. It grows in row

crops, such as soybeans, corn, and cotton. Seeds

may be spread by irrigation water, animals,

birds, crop seeds, and other carriers. Barnyardgrass greatly reduces rice yields.

CONTROL.—Water seeding, flooding young

plants, rotations, good land preparation, land

leveling, and herbicides help control barnyardgrass.

Most species and varieties of barnyardgrass

do not germinate under water; therefore, this

weed may be controlled by continuous submergence of the land or by seeding the rice in

water. The land should be covered with 4 to 8

inches of water immediately before or after

emergence of barnyardgrass plants.

Adequate land preparation, proper levee construction, and land leveling for maintenance of

a uniform depth of water help control barnyardgrass. Delayed planting of rice controls

barnyardgrass, since the land may be prepared

early in the spring and disked every 2 or 3

weeks to kill grass plants as they emerge. The

last cultivation should be shallow (2 to 3

inches) to prevent bringing deeply buried seed

to the soil surface.

Rotations, such as row crops and rice or

small grains and rice, help control barnyardgrass. It should be controlled in the row crop

by cultivation or herbicides or both. Small

grain crops, such as oats or wheat, rotated with

rice help control barnyardgrass, because the

land may be clean fallowed during the summer

after the small grain has been harvested.

Barnyardgrass can be controlled either by

propanil at 3 or 4 pounds per acre applied at

the 1- to 3-leaf stage or CIPC at 6 to 8 pounds

applied just before or immediately after emergence. See pages 12 and 18 for more details

on chemical control of barnyardgrass.

Beakrush (figs. 12 and 13)

Rhynchospora cornkulata (Lam.) Gray

OTHER NAMES.—Spearhead, hornedrush, umbrellaweed, tadpole-sedge, and ace-of-spades.

PRINCIPAL SPECIES.—ß. cormcuMa is the

only species of economic importance in rice.
40 AGR. HANDB. 292, U.S. DEPT. OF AGRICULTURE

FIGURE 12.—Beakrush (Rhynchospora comiculata), whole plant.
WEEDS AND THEIR CONTROL IN RICE PRODUCTION 41

DESCRIPTION.—Beakrush is a perennial that

reproduces by seeds and rhizomes. Stems are

stout, leafy, triangular, and from 2 to 6 feet

tall. Leaf blades have a rough margin. The

inflorescence is widely branched. Seeds are

about 1^ inch long, have beaks Va to % inch

long, and are extremely difficult to separate

from the rice seed.

Brachiaria (fig. 14)

Brachiaria platyphylla (Griseb.) Nash

OTHER NAME.—Signalgrass.

PRINCIPAL SPECIES.—No others

DESCRIPTION.—Brachiaria is an annual that

reproduces by seed. Young plants are similar

to crabgrass seedlings, but they have shorter

wider leaves. Seeds are about twice as large as

crabgrass seed. Brachiaria plants are about

1 to 2 feet tall when mature.

FIGURE 14.—Brachiaria (Brachiaria platyphylla).

FIGURE 13.—Beakrush, panicle.

DISTRIBUTION.—Beakrush is a troublesome

weed in the southern ricegrowing areas. It

grows in ricefields, canals, ditches, and other

wet areas. It competes with rice to reduce

yields, interferes with harvesting and drying,

and reduces quality of rice.

CONTROL.—Rotations, good seedbed preparation, cultivation, and drainage help control

beakrush. Propanil at 3 to 4 pounds per acre

appHed to plants 3 to 4 inches tall kills beakrush.

DISTRIBUTION.—Brachiaria grows only in the

southern rice area. It grows well in the rice

crop, on levees, and along edges of canals. It

reduces yields by competition with rice early

in the growing season.

CONTROL.—Brachiaria germinates well in

moist soil but not under water. Water-seeding

of rice discourages brachiaria. Proper seedbed

preparation, rotations, land leveling, and fallowing help control this weed. Propanil at 3 or

4 pounds per acre applied to young plants in

the 1- to 3-leaf stage kills brachiaria.
42 AGR. HANDB. 292, U.S. DEPT. OF AGRICULTURE

Bulrush (fig. 15)

Scirpus spp.

PRINCIPAL SPECIES AND COMMON NAMES.—

Scirpus mucronatus L. (fig. 16) called roughseed bulrush; S. fluviatilis (Torr.) Gray called

river bulrush; and S. acutus Muhl. called hardstem bulrush and great bulrush.

DESCRIPTION.—Most of the bulrushes troublesome in rice and all principal species are

perennial plants that reproduce by seed, rhizomes, or rootstocks. Scirpus mucronatus and

S. fluviatilis have triangular, stout culms that

grow 2 to 4 feet tall. S. acutus has round, erect

culms ranging from 3 to 6 feet tall.

DISTRIBUTION.—Bulrushes are troublesome

in most rice-producing States. Scirpus mucroFlGURE 15.—Bulrush {Scirpus acutus). FIGURE 16.—Koughseed bulrush

{Scirpus mucronatus).
WEEDS AND THEIR CONTROL IN RICE PRODUCTION 43

natus and S. fluviatilis grow in California, but

the former is more serious because it infests

large acreages of rice. Bulrushes in the Southern United States may infest poorly drained

ricefields, drainage and irrigation canals,

ditches, reservoirs, and other wet areas. They

compete with rice, lower yields, interfere with

harvest, and impede flow of water in canals

and ditches.

CONTROL.—Scirpus mucronatus is controlled

in ricefields by 2,4-D or MCPA at 1 pound per

acre. But most bulrushes are not controlled

selectively in rice with herbicides. Cultural

control methods, such as rotations, land leveling, good seedbed preparation, cultivation, and

mowing, therefore, are used in the rice crop.

Bulrushes infesting uncultivated areas may be

killed with low-volatile esters of 2,4-D at 4 to

8 pounds per acre, dalapon at 15 to 20 pounds,

or amitrole at 6 to 10 pounds. Repeated applications may be necessary. Addition of 5 to 10

gallons of diesel oil per acre to the dalapon

spray solution greatly increases effectiveness.

Dalapon and amitrole are safer to use near

crops sensitive to 2,4-D.

Burhead (fig. 17)

creepmg

Echinodorus cord'ifoHus (L.) Griseb.

OTHER NAMES.—Mudbabies and

waterplantain.

PRINCIPAL SPECIES.—E. cordifolms is the

only species of economic importance in rice.

DESCRIPTION.—Burhead is an aquatic,

emersed, erect annual that reproduces by seed.

Plants are 24 to 48 inches tall and bear many

whorls of flowers. Leaves have long petioles;

leaf blades are egg shaped, have heart-shaped

FIGURE 17.—Burhead (Echinodorus cordifolius). Courtesy of the University of California.
44 AGR. HANDB. 292, U.S. DEPT. OF AGRICULTURE

laases, and are up to 10 inches long and 5 or 6

inches wide. The seed cluster resembles a bur

and is 1/2 to 1 inch in diameter. Seeds are

about 1/10 inch long, sharply ridged, and short

beaked.

DISTRIBUTION.—Burhead grows in most riceproducing States. It frequently grows in ricefields, shallow irrigation and drainage canals,

ditches, potholes, sloughs, and other wet areas.

It is most troublesome in areas where rice

stands are thin or where cold water enters the

ricefield. Burhead germinates and emerges

under water.

CONTROL.—Burhead is controlled by gogd

seedbed preparation, adequate stands of rice,

drainage, and herbicides. It is very susceptible

to phenoxy herbicides. MCPA and 2,4-D at %

to IV2 pounds per acre give control. These

herbicides should be applied when rice is in the

"tolerant" stage of growth (p. 24).

Cattail (fig. 18)

Typha spp.

OTHER NAMES.—Flags, tules, and reedmace.

PRINCIPAL SPECIES.—Typha angustifolia L.,

T. domingensis Pers., T. glauca Godr., T. latifolia L.

DESCRIPTION.—Species of cattails are perennials that reproduce by rootstocks and by

minute, airborne seeds that germinate readily

in mud and occasionally in shallow, clear water.

The plants are erect and have long, narrow

leaves. The flowers are in a long and very

dense cylindrical spike terminating the stem.

There is an extensive rhizome system. Plants

are 4 to 8 feet tall and usually grow in colonies.

Seeds may remain viable for 5 years or more.

DISTRIBUTION.—Cattails grow in all riceproducing States, but all species are not found

in each State. They grow in shallow water in

irrigation and drainage ditches and may grow

in the rice crop where drainage is inadequate.

CONTROL.—Cattails may be controlled by

drainage and cultivation. If they are serious in

low areas of ricefields, they may be controlled

by drainage, summer fallowing, and cultivation. Cattails may be controlled also by cutting

them close to the ground at two special stages

of growth. The first cutting should be made

when the heads are two-thirds of full size but

not mature enough to scatter viable seed. The

second cutting should be made about a month

later when regrowth has attained a height of

about 2 feet.

No herbicide will selectively kill cattails

without injuring rice. Cattails may be controlled chemically in uncultivated areas with

low-volatile esters of 2,4-D at 4 to 6 pounds per

acre. Use in a 1 to 20 oil-water emulsion with

a total volume of 1-50 to 300 gallons per acre

applied as a foliage spray. The first spray

treatment should be made just before heading

of cattails, and the treatment will need to be

FIGURE 18.—Cattail (Typha latlfolia).
WEEDS AND THEIR CONTROL IN RICE PRODUCTION 45

repeated on regrowth. About three applications over a 2-year period are necessary for

complete control. Dalapon at 15 to 20 pounds

per acre or amitrole at 6 to 10 pounds applied

in late summer after heads are firm control

cattails. The addition of 5 to 10 gallons of

diesel oil per acre to the dalapon spray solution

greatly improves effectiveness. Repeated applications may be necessary. Dalapon and amitrole are safer to use near crops sensitive to

2,4-D.

Curly Indigo (fig. 19)

Aeschynomene virginica (L.) B.S.P,

OTHER NAMES.—Sensitive jointvetch, northern jointvetch, indigo, bashfulweed, and coffeeweed.

PRINCIPAL SPECIES.—No others.

DESCRIPTION.—Curly indigo is an erect,

leguminous annual that reproduces by seed.

Stems are branched, sparsely bristled at base

FIGURE 19.—Curly indigo (Aeschynomene virginica).
46 AGR. HANDB. 292, U.S. DEPT. OF AGRICULTURE

but abundantly bristled near apex, and 2 to 5

feet tall. Leaves are compound, are short

petioled, and have 25 to 55 linear-oblong leaflets

that fold when touched. Stipules are large and

deciduous, especially those below the tip of the

stem. Inflorescence is axillary, is often leafy,

and contains 1 to 6 yellow, red-veined flowers.

Pods are 1 to 3 inches long and segmented into

4 to 10 nearly square joints that separate easily

at maturity. Young plants may be identiñed

by large stipules (fig. 20) and bristly stems

near the shoot apex. Seeds are kidney shaped

and viable for many years in the soil.

FIGURE 20.—Left, Sesbania, showing small narrow

stipules; right, curly indigo, showing large stipules.

DISTRIBUTION.—Curly indigo is a serious

weed in the southern rice-producing areas. It

grows in the rice crop, on field levees, in uncultivated fields and waste areas, along canal and

ditch banks, and in other areas. It competes

with rice, interferes with harvest, and reduces

quality because its seeds are difficult to remove

from rough and milled rice.

CONTROL.—Curly indigo is controlled by rotations, fallowing, cultivation, good seedbed preparation, water seeding, hand pulling, and herbicides. Rotations of either row crops or pasture

and rice help control this weed. It may be controlled in row crops by cultivation and in pasture by grazing and mowing. Summer fallowing with timely and thorough cultivation

controls it. Water seeding controls curly indigo

because seeds do not germinate when covered

with water. Hand pulling is practical when only

a few scatterd plants are present.

Curly indigo is susceptible to phenoxy herbicides. Silvex and 2,4,5-T are more effective

than 2,4-D. Silvex and 2,4,5-T at 1 to II/2

pounds per acre control this weed. Usually

2,4-D at 11/2 to 2 pounds controls it, but it is

not killed by 2,4—D even at a rate of 2 pounds.

Curly indigo plants should be sprayed when

they are 1 to 3 feet tall. Phenoxy herbicides

should be applied when rice is in the "tolerant"

stage of growth (p. 24).

Ducksalad

Heteranthera spp.

OTHER NAMES.—Mudplantain and waterlily.

PRINCIPAL SPECIES.—Heteranthera limosa

(Sw.) Willd. (fig. 21) and H. reniformis R. & P.

DESCRIPTION.—Species of ducksalad are

aquatic annuals that reproduce by seed. Leaf

shape and flower number diñ"erentiate Heteranthera limosa and H. reniformis. Leaves of H.

limosa are oval, narrow, and I/2 to 5 inches

long; the inflorescence has only one flower.

Leaves of H. reniformis are kidney to heart

shaped and 1 to 3 inches long and about as

broad; the inflorescence has two or more

flowers. Ducksalad seeds are borne in a dehiscent capsule that contains many minute,

ridged, black seeds.

DISTRIBUTION.—Ducksalad is a serious ricefield weed in the southern ricegrowing area.

It grows in the rice crop, in shallow water in

irrigation and drainage canals, and in ditches,

potholes, sloughs, and other wet areas. It is

particularly troublesome in water-seeded rice.

Seeds germinate under water as soon as the

field is flooded. The young plants compete with

rice early in the growing season and reduce

yields.

CONTROL.—Land leveling, drainage, good rice

stands, and herbicides help control ducksalad.

Land leveling eliminates potholes and promotes

drainage of the land. Ducksalad may be killed

by thoroughly drying the soil to where it cracks

open. Drying kills young plants more easily

than old ones.

Herbicides, including propanil, 2,4,5-T, silvex, and 2,4-D, kill ducksalad. Propanil at 3

or 4 pounds per acre applied to very young
WEEDS AND THEIR CONTROL IN RICE PRODUCTION 47

FIGURE 21.—Ducksalad (Heteranthera limosa).

ducksalad plants in the 1-leaf stage, or 1 to 2

inches tall, controls this weed, but it does not

kill old or large ones. Silvex and 2,4,5-T at

1 to 11/2 pounds per acre control ducksalad

fairly well, but young plants are more easily

controlled than old ones. Ducksalad is more

susceptible to 2,4-D than to 2,4,5-T or silvex.

It is controlled effectively by % to II/2 pounds

per acre of 2,4-D applied when rice is in the

"tolerant" stage of growth (p. 24), but 2,4,5-T

at 11/2 pounds may give only partial control.

If ducksalad becomes serious when rice is

4 to 6 weeks old, 2,4,5-T at % to 1 pound per

acre may be applied for partial control. Later,

when rice is in the "tolerant" stage of growth,

an application of 2,4-D may be required.

Fimbristylis (fig. 22)

Fimbristylis spp.

OTHER NAME.—Hoorahgrass.

PRINCIPAL SPECIES.—Fimbristylis autumnalis (L.) R. & S. and F. miliacea (L.) Vahl.

DESCRIPTION.—Species of Fimbristylis are

annuals that reproduce by seed. Plants are

turflike in growth. The culms are slender, erect FIGURE 22.—Fimbristylis (Fimbristylis viiliacea).
48 AGR. HANDB. 292, U.S. DEPT. OF AGRICULTURE

to diffuse, leafy at the base, 12 to 18 inches

tall at maturity, and weak; and they lodge

easily. The leaf blades are narrow and short.

The inflorescence is open and has several small

foliagelike bracts of variable length at its base.

DISTRIBUTION.—Fimbristyhs is troublesome

only in the Southern United States. It grows in

the rice crop, on field levees, along canals, and

in other wet areas. It competes with rice and

reduces yields.

CONTROL.—Fimbristylis is controlled by

good seedbed preparation, proper water management, good stands of rice, and herbicides.

Propanil at 3 to 4 pounds per acre kills young

plants. Phenoxy herbicides, including 2,4-D,

2,4,5-T, and silvex, at V2 to IV2 pounds per

acre control this weed. Phenoxy herbicides

should be applied to rice in the "tolerant" stage

of growth (p. 24).

Gooseweed (fig. 23)

Sphenoc/ea zeylanica Gaertn.

OTHER NAME.—Hollowstem.

PRINCIPAL SPECIES.—No others.

DESCRIPTION.—Gooseweed is an aquatic annual that reproduces by seed. Stems are erect,

smooth, hollow, and 1 to 5 feet tall. Leaves are

elliptical to linear, smooth margined, 1 to 4

inches long, light green—paler beneath than

above. Flowers are borne in a continuous dense

spike and are white or greenish.

DISTRIBUTION.—Gooseweed grows in the

Southern United States. It grows in the rice

crop where stands are thin, in irrigation and

drainage canals, in ditches, along levees, and in

other wet areas. It competes with rice and,

when it is green and succulent, interferes with

harvest.

CONTROL.—Gooseweed may be controlled by

rotations, good seedbed preparation, cultivation, land leveling, drainage, good stands of

rice, and herbicides. Where stands of rice are

adequate and uniform and water is managed

correctly, gooseweed is no problem.

Silvex, 2,4-D, and 2,4,5-T at 1 to II/2 pounds

per acre will greatly reduce competition of

gooseweed with rice. Sometimes, however,

these herbicides give only partial control because gooseweed is relatively tolerant. Gooseweed is stunted by the treatment, but often

recovers. Gooseweed is more susceptible to

2,4,5-T and silvex than to 2,4-D. The latter

herbicide should be applied when rice is in the

"tolerant" stage of gro\vth (p. 24). Silvex and

2,4,5-T at % to 1 pound per acre applied 4 or 5

weeks after emergence of rice give some control. Not more than 1 pound per acre should

be applied at this time.

In uncultivated areas, such as ditches and

drainage canals, 2,4-D, 2,4,5-T, or silvex may

be applied at 2 to 4 pounds per acre to control

gooseweed. Oil- or water-carried sprays may

be used, but oil is more effective. Surfactants

increase the effectiveness of the phenoxy herbicides applied as water sprays.

FIGURE 23.—Gooseweed (Sphenoclea zeylanica).

Knotgrass

Paspalum spp.

PRINCIPAL SPECIES AND COMMON NAMES.—

Paspalum distichum L. called knotgrass, water

bermudagrass, jointgi^ass, and lakegrass; P.

hvidtim Trin. known commonly as longtom,

doggrass, and watergrass; and P. aciminatum
WEEDS AND THEIR CONTROL IN RICE PRODUCTION 49

Raddi. called brookpaspalum, watergrass, and

crawlinggrass.

DESCRIPTION.—All principal species are

perennials that reproduce by seed and creeping

runners. Paspalum distichtim has stolons often

growing 25 feet long, and the leaf blades are

relatively short—1 to 3 inches long. It has two

racemes, or seed heads, which are ascending,

often incurved, and 1 to 2 inches long. P. lividum is a smooth, creeping grass with culms 20

to 40 inches long. Leaf blades are 6 to 10

inches long and purple at the tip. The seedstalk bears several, usually 4 to 7, dark-purple

racemes. P. acuviinatum resembles P. lividum,

but leaf blades are shorter and wider and have

a very light-colored midrib. Seed heads bear

3 to 5, usually 3, erect or ascending racemes

that are 2 to 3 inches long.

DISTRIBUTION.—Knotgrass grows in all riceproducing areas, but longtom and brookpaspalum grow only in southern Louisiana and

Texas. They are usually most troublesome

when the rice is young and in irrigation and

drainage canals where they impede the movement of water. These weeds compete with rice

and reduce yields.

CONTROL.—Species of knotgrass are controlled by cultural practices, such as good

drainage, fallowing with intensive and timely

cultivation in the summer, and good seedbed

preparation. In t?ie rice crop, cultural methods

are useful because paspalums cannot be removed selectively from rice with herbicides.

In canals, ditches, and other uncultivated areas,

knotgrass and other paspalums may be controlled with dalapon at 5 to 10 pounds per acre

applied when the creeping runners are 2 to 6

feet long. The spray volume should be sufficient

to adequately cover the plants. Activity of

dalapon on these weeds is enhanced by the

addition of a surfactant at 0.1 percent by

weight to the spray solution. Dalapon should

not be sprayed on rice.

Mexican-weed (fig. 24)

Caperonia castaneaefoHa (L.) St. Hil.

OTHER NAMES.—Birdeye and Texas-weed.

PRINCIPAL SPECIES.—No others.

DESCRIPTION.—Mexican-weed is a tough,

fibrous-rooted annual that reproduces by seed.

Leaves are alternate, about 2 inches wide, 3 to

5 inches long, prominently veined, coarsely

toothed on margin, and petioled. The stem is

rough, hairy, and 2 to 3 feet tall. It has small

white flowers and a burlike fruit. Seeds are

spherical, gray with distinctive light-colored

markings, and about one-eighth inch in diameter.

DISTRIBUTION.—Mexican-weed is troublesome

in Louisiana and Texas. It grows in the rice

crops, on levees, and in other wet areas. It

competes with rice, interferes with harvesting,

and lowers quality because its seeds are difficult

to separate from rough and milled rice.

CONTROL.—Rotations, good seedbed preparation, hand pulling, and herbicides control Mexican-weed. Silvex, 2,4,5-T, and 2,4-D at 1 to

IV2 pounds per acre control this weed, but silvex and 2,4,.5-T are more efliective than 2,4-D.

Apply phenoxy herbicides when rice is in the

"tolerant" stage of growth (p. 24).

y

FIGURE 24.—Mexican-weed (Caperonia castaneaefoHa).

Morningglory

Ipomoea spp.

PRINCIPAL SPECIES AND COMMON NAMES.—

Ipomoea Uicxinosa L. called small-flowered

morningglory (fig. 25); /. hederacea (L.) Jacq.

called ivyleaf morningglory; and /. prirpurea

(L.) Roth called common morningglory.
50 AGR. HANDB. 292, U.S. DEPT. OF AGRICULTURE

FIGURE 25.—Small-flowered morningglory (Ipomoea lacunosa).

DESCRIPTION.—Species of morningglory are

twining annuals that reproduce by seed. Stems

are hairy and 3 to 15 feet long. Leaves of

Ipomoea lacunosa and /. purpurea are heart

shaped, but those of /. hederacea are deeply 3-

lobed with rounded sinuses. Flowers are solitary on axillary peduncles or in clusters, funnel

shaped, and white, purple, or pale blue. Seeds

are about one-quarter inch long, are dark

brown to black, and have one round and two

flattened sides.

DISTRIBUTION.—Morningglories are troublesome in rice in the southern rice-producing

areas. They grow on ricefield levees and on

banks of irrigation and drainage canals. They

do not grow in water; therefore, they are not

troublesome between the levees. Morningglories

interfere with harvest and lower the quality of

rice because the seeds are difficult to separate

from rough and milled rice.

CONTROL.—Rotation of row crops and rice,

cultivation, and the use of herbicides help control morningglories. They may be controlled on

ricefield levees by spraying with silvex, 2,4-D,

or 2,4,5-T at % to IV2 pounds per acre. Phenoxy herbicides should be applied when rice is

in the "tolerant" stage of growth (p. 24). Propanil at 3 or 4 pounds per acre controls morningglories in the cotyledonary stage of growth,

but it does not kill those having one or more

leaves.

Red Rice (figs. 26 and 27)

Oryza sativa L.

OTHER NAMES.—Vermillion red rice, Italian

red rice, and common red rice.

PRINCIPAL TYPES.—Red rice is a variety of

rice, and there are many types.

DESCRIPTION.—Red rice is an annual that

reproduces by seed. It usually matures before

FIGURE 26.—Red rice (Oryza sativa), whole plant.
WEEDS AND THEIR CONTROL IN RICE PRODUCTION 51

white rice. It has a red seedcoat, which may

vary in redness, instead of the usual brown

one. It has a more spreading growth than

white rice. The heads are loose, open, and

lightly drooping. The grains shatter readily

when ripe and may be short, medium, or long.

Sometimes the grains must be hulled to expose

the red seedcoat before red rice can be distinguished from the white rice. Some varieties

have long awns on the spikelet.

FIGURE 27.—Red rice, panicles.

DISTRIBUTION.—Red rice is a serious weed in

all rice-producing States. It grows in the rice

crop, in irrigation and drainage canals, on

levees, and in other wet areas. It reduces yields

and quality of rough and milled rice. Kernels

of red rice are difficult to separate from the

milled white rice.

CONTROL.—Red rice is spread largely by

using seed containing red grains. The use of

high-quality rice seed prevents establishment

of red rice on the land. Red rice is difficult to

control once it is established, because the seeds

shatter easily and persist in the soil for several

years. Rotations, fallowing, cultivation, land

leveling, and grazing help control red rice.

When row crops are rotated with rice, red

rice plants may be killed by cultivating the

row crop. When a small grain crop, such as

oats, is rotated with rice, the land may be

summer fallowed with diskings timed to kill

red rice plants. Disking brings dormant seeds

to the soil surface, where they germinate and

are killed by successive cultivations. The cultivation just before planting rice should be shallow to prevent bringing more red rice seed to

the soil surface. When pasture is rotated with

rice, the grazing prevents seed production of

red rice. Hand pulling scattered plants in commercial rice to prevent red rice from spreading

and becoming more serious is feasible where

infestations are light.

Redstem (fig. 28)

Ammannia coccínea Rothb.

OTHER NAME.—Toothcup.

PRINCIPAL SPECIES.—Ammannia coccínea is

the only species of economic importance in rice.

DESCRIPTION.—Redstem is an aquatic annual

that reproduces by seed. Stems are square,

often freely branched, and 8 to 40 inches tall.

Leaves are narrow (about 1/2 i^^h wide), 1 to

4 inches long, and clasping at the base. Flowers

are borne in the axils of the leaves. Seeds are

produced in spherical capsules that are onetenth to one-fifth inch in diameter. The plant

turns red at maturity.

DISTRIBUTION.—Redstem is a serious ricefield weed in all rice-producing states. It

grows in the rice crop, along levees, ditches,

and canals, and in other wet areas. It F"'^^

especially well where rice stands are thin. It

reduces yields, lowers quality, interferes with

harvesting, and increases cost of drying when

green capsules are present in rough rice.

CONTROL.—Rotations, good seedbed PjeP^T^-

tion, cultivation, good stands of rice, and herbicides control redstem. Redstem is very susceptible to phenoxy herbicides. Silvex, ^4-L»,

2,4,5-T, and MCPA at 1/2 to II/2 pounds per
52 AGR. HANDB. 292, U.S. DEPT. OF AGRICULTURE

acre applied to plants 1 to 2 feet tall control

this weed. Phenoxy herbicides should be applied when rice is in the "tolerant" stage of

growth (p. 24). Propanil at 3 to 4 pounds per

acre kills small redstem plants 2 inches tall,

but it does not control large ones.

FIGURE 28.—Redstem {Aimnannia coccínea).

Sesbania (fig. 29)

Sesbania exaltata (Raf.) Cory

OTHER NAMES.—Coffeebean, cofFeeweed, tallindigo, and sennabean.

PRINCIPAL SPECIES.—No others.

DESCRIPTION.—Sesbania is a tall, erect,

smooth, leguminous annual that reproduces by

seed. It may grow 12 to 15 feet tall. Leaves

are compound, with 12 to 25 pairs of leaflets.

Flowers are yellow and usually mottled with

purple. Pods are long, narrow, compressed,

and 6 to 12 inches long; they have numerous

seeds separated by transverse partitions. Seeds

are small and oblong; they may be viable in the

soil for many years. Young plants of sesbania

resemble those of curly indigo, but they may

be identified by the small narrow bract or

stipule, the smooth stem (fig. 20), and the

simple leaf that emerges just after the cotyledons.

DISTRIBUTION.—Sesbania is a serious weed in

the southern rice-producing areas, but it does

not grow on the West Coast. It grows in the

rice crop, on field levees, in uncultivated fields

and waste areas, along canals and ditchbanks,

in row crops, and other places. It competes

with rice, interferes with harvest, and reduces

quality because its seeds are difficult to remove from rough and milled rice.

CONTROL.—Sesbania is controlled by rotation, fallowing, cultivation, good land preparation, water seeding, hand pulling, and herbicides. Rotations of row crops or pasture and

rice help control this weed. Sesbania may be

controlled in row crops by cultivation and in

pasture by grazing and mowing. Summer fallowing land with timely and thorough cultivation controls sesbania. Water seeding controls

FIGURE 29.—Sesbania (Sesbania exaltata) in rice.
WEEDS AND THEIR CONTROL IN RICE PRODUCTION 53

sesbania because seeds do not germinate when

they are covered with water. Hand pulling

sesbania plants is practical when only a few

scattered plants are present.

Sesbania may be controlled with 2,4-D, 2,4.

5-T, and silvex at rates of 1 to IV2 pounds per

acre. Plants should be sprayed when they are

2 to 6 feet tall. Phenoxy herbicides should be

applied when rice is in the "tolerant" stage of

growth (p. 24). Propanil at 2 to 3 pounds per

acre kills young sesbania plants; it is most

effective when the plants are 4 to 24 inches tall.

Smartweed (fig. 30)

Polygonum spp.

OTHER NAMES.—Knotweed and pepperweed.

PRINCIPAL SPECIES.—Numerous species of

smartweed infest rice; therefore, no specific

breakdown is given.

DESCRIPTION.—Some species of smartweed

are annual herbs and others are perennial;

some species grow erect and others are prostrate. The plants are usually 2 to 6 feet tall.

The stems have thick joints, and the leaves are

alternate, linear, and short petioled. Flowers

are in axillary clusters or in spikes and panicles, often nodding. Seeds are a 3-angled

achene, small, and dark brown to black; and

they have a hard seedcoat.

DISTRIBUTION.—Smartweeds grow in all riceproducing States. They grow in the rice crop

where cultivation and drainage are poor, on

ricefield levees, in drainage and irrigation

canals, in potholes and sloughs, and in other

wet areas. Smartweeds often grow in shallow

water since some are true aquatics, but others

grow on uplands. They reduce rice yields, interfere with harvesting and drying, and lower

quality of rice.

CONTROL.—Smartweeds are controlled by

cultivation, good seedbed preparation, drainage, and herbicides. Smartweeds growing on

ricefield levees may be partially controlled with

2,4-D, 2,4,5-T, silvex, or MCPA at rates of 1 to

11/2 pounds per acre. Usually rates of 4 to 8

pounds are required to kill smartweeds, but

rates of 1 to IV2 pounds inhibit growth and

prevent seed production. Only rates of 1 to IV2

pounds may be used in the rice crop. Phenoxy

herbicides should be applied when rice is in the

"tolerant" stage of growth (p. 24). Smartweeds may be controlled in uncultivated areas,

including canals, ditches, and reservoirs, with

low-volatile esters of 2,4-D at 4 to 8 pounds

per acre applied in fuel oil at 100 gallons per

acre and with amitrole-T at 1 to 2 pounds applied in 100 to 200 gallons of water per acre.

FIGURE 30.—Smartweed (Polygonum spp.]

Spikerush (fig. 31)

E/eochor/s spp.

PRINCIPAL SPECIES AND COMMON NAMES.--

Eleocharis obtusa (Willd.) Schultes (annual)

called blunt spikerush; E. párvula (R. & S.)

Link (annual) called dwarf spikerush and niggerhair; E. palustris (L.) R. & S. (perennial)

called creeping spikerush (fig. 32), common

spikerush, and wiregrass; E. quadrangulata

(Michx.) R. & S. (perennial) called squarestem spikerush or four-square; and others.

DESCRIPTION.—Species of this genus are

annuals or perennials that reproduce by seed,

or rhizomes, or both. Plants are turflike in

growth and have simple, round culms that are

erect or slightly reclining and terminated by
54 AGR. HANDB. 292, U.S. DEPT. OF AGRICULTURE

a seed head. Leaves are bladeless sheaths.

Plants of Eleocharis obtusa have blunt-tipped

sheaths and are 12 to 20 inches tall at maturity.

E. párvula is one of the smallest spikerushes;

it grows only 1 to 4 inches tall. E. palustris has

a creeping growth and grows about 3 feet tall.

E. quadrangulata has stout, thick, sharply 4-

angled culms growing to a height of 3 feet.

DISTRIBUTION.—Spikerushes grow in all riceproducing States. Eleocharis palustris is especially troublesome in California. Spikerushes

grow in the rice crop, on field levees, in shallow

ditches, and on poorly drained soil. E. obtusa

and E. párvula are especially troublesome in

water-seeded rice. They compete with rice in

the early growing season and may reduce yields

greatly.

CONTROL.—Spikerushes are controlled by

drainage, adequate seedbed preparation, and

deep and repeated cultivation. Presence of

perennial spikerushes in ricefields often indicates poor seedbed preparation or poor drainage. Eleocharis palustris does not germinate

well under continuous flooding; therefore, seeding rice in the water helps control it. Annual

spikerushes, such as E. obtusa and E. párvula,

FIGURE 31.—Blunt spikerush {Eleocharis obtusa). FIGURE 32.—Creeping spikerush

{Eleocharis palustris).

A
WEEDS AND THEIR CONTROL IN RICE PRODUCTION 55

are controlled with herbicides, including propanil, 2,4-D, MCPA, 2,4,5-T, and silvex. Propanil at 3 to 4 pounds per acre kills young annual spikerush plants. Phenoxy herbicides at

1/2 to IV2 pounds per acre kill young or old

annual spikerushes. They should be applied to

rice in the "tolerant" stage of growth (p. 24).

Perennial spikerushes infesting rice cannot be

controlled with herbicides because 4 to 8

pounds per acre is required for control. When

spikerushes grow in uncultivated areas, they

may be controlled with 2,4-D, 2,4,5-T, or silvex

at 4 to 8 pounds per acre in sufficient water or

fuel oil to cover foliage.

Sprangletop (figs. 33 and 34)

Lepfoch/oa spp.

OTHER NAMES.—Raygrass, Christmastreegrass, and feathergrass.

PRINCIPAL SPECIES.—Leptochloa panicoides

(Presl.) Hitchc. and L. fascicularis (Lam.)

Gray.

DESCRIPTION.—Species of sprangletop which

are weeds in rice are annuals that reproduce

from very small seeds seldom found in rough

rice. The plants have fine stems terminated

in a panicle, grow 2 to 3 feet tall, and tiller

heavily.

DISTRIBUTION.—Sprangletop is present in all

rice-producing States. Leptochloa panicoides

does not grow in California, but it grows in the

other rice-producing States. Sprangletop grows

in shallow water along canals, in the rice crop,

and on field levees. It is particularly serious

where stands of rice are thin. It grows especially well on the heavy clay soils in the

Mississippi River bottom lands.

CONTROL.—Seeds of sprangletop do not germinate well under water, but after germination

the young plants grow through water more

quickly than rice does. Water seeding discourages sprangletop, and a good stand of rice helps

control it. Propanil at 3 or 4 pounds per acre

usually does not control Leptochloa fascicularis,

but these rates applied postemergence to young

plants in the 1- to 2-leaf stage reduce competition of L. panicoides with rice.

FIGURE 33.—Sprangletop (Leptochloa panicoides). FIGURE 34.—Sprangletop (Leptochloa fascicularis).
56 AGR. HANDB. 292, U.S. DEPT. OF AGRICULTURE

Umbrellasedge

Cyperus spp.

PRINCIPAL SPECIES AND COMMON NAMES.—

Cyperus erythrorhizos Muhl. (fig. 35) (annual)

called redroot flatsedge; C. articukitus L. (perennial) called jointed flatsedge, jointed sedge,

and onions; C. Iria L. (fig. 36) (annual) called

umbrellasedge; C. difformis L. (annual) called

sedge; C. strigosus L. (perennial) called strawcolored sedge (fig. 37); and C. esculentus L.

(perennial) called yellow nutsedge.

FIGURE 35.—Redroot flatsedge (Cyperus erythrorhizos).

DESCRIPTION.—Species of this genus are annuals and perennials that reproduce by seed or

tubers, or both. The general appearance of

plants within each species of Cyperus may vary

greatly. The plants of most species of Cyperus

have a triangular flower stalk bearing a headlike or branch inflorescence. At the base of the

inflorescence there are foliagelike bracts that

vary in size and number in the various species.

Most umbrellasedge plants grow 1 to 2 feet tall.

FIGURE 36.—Umbrellasedge (Cyperus Iria).

DISTRIBUTION.—Umbrellasedges grow in all

rice-producing States. Cyperus erythrorhizos

and C. Iria are troublesome in the southern

rice-producing areas and C. difformis is prevalent in California. They grow in the rice crop,

in and along irrigation and drainage canals, on

levees, in sloughs, and in other poorly drained

areas. The perennial types, except C. esculentus, usually are prevalent in poorly drained

areas, such as idle ricefields; but may infest rice

when seedbed preparation is inadequate. The

annual umbrellasedges are more troublesome in

the rice crop than perennials. C. erythrorhizos,

C. Iria, and C. difformis are especially troublesome where rice stands are thin; they ordinarily

appear late in the season after the land has

been submerged for some time. Umbrellasedges

reduce yields, interfere with harvesting, and

lower rice quality.

CONTROL.—Rotations, land preparation, cultivation, drainage, good rice stands, and herbicides help control umbrellasedges. Some umbrellasedges, especially annuals, may infest ricefields even with good cultural practices. Silvex,

MCPA, 2,4-D, and 2,4,5-T at 1 to II/2 pounds
i

WEEDS AND THEIR CONTROL IN RICE PRODUCTION 57

äSww ^*v„^^^

" «¡7/ Lp "^

-^

/

—

/

\r\,

/A\t-^

—

íÉjátifiríhi il^K.«^ i. .-3

FIGURE 37.—Straw-colored sedge (Cyperus strigosus).

per acre control Cyperns eryfhrorhizoH, C. Iria

and some other annual sedges, but they do not

control C. difformis satisfactorily. Phenoxy

herbicides, however, may give partial control of

some of the perennial sedges. Phenoxy herbicides should be applied to rice during the

"tolerant" stage of growth (p. 24). Propanil

at 3 to 4 pounds per acre controls young umbrellasedge; it usually controls the annuals better than the perennials.

Waterhyssop (fig. 38)

Bacopa rotundifolia (Michx.) Wettst.

OTHER NAMES.—No others.

PRINCIPAL SPECIES.—B. rotundifolia is the

only species of economic importance in rice.

DESCRIPTION.—Waterhyssop is an aquatic annual that reproduces by seed. Stems, 8 to 24

inches long, are submerged with the tips floating; they are pubescent when young. Leaves are

thin, round, clasping at the base, and palmately

veined. Flowers, 2 to 4 at each node, are

white with a yellow throat, pediceled, and

axillary.

DISTRIBUTION.—Waterhyssop grows in all

ricegrowing States. It is usually associated

with other aquatic weeds, such as ducksalad;

and it is most serious where stands of rice are

thin or where rice is seeded in water. It

grows in the rice crop, shallow ditches and

FIGURE 38.—Waterhyssop (Bacopa rotundifolia).
58 AGR. HANDB. 292, U.S. DEPT. OF AGRICULTURE

canals, and other wet areas. It competes with

rice during the early growing season and

may reduce tillering and yields.

CONTROL.—Waterhyssop is controlled by

drainage, good rice stands, and herbicides. It is

very susceptible to phenoxy herbicides. Silvex,

2,4-D, MCPA, and 2,4,5-T at 1/2 to 1 pound

per acre control it effectively. Silvex and 2,4,

5-T may be applied as early as 4 or 5 weeks

after emergence and MCPA may be applied as

early as 6 weeks after emergence without damaging rice. However, 2,4-D should not be applied until the rice is in the "tolerant" stage of

growth (p. 24).

Waterplantain (fig. 39)

Atisma triviale Pursh

OTHER NAMES.—Common waterplantain and

waterlily.

PRINCIPAL SPECIES.—Alisma triviale is the

only species of economic importance in rice.

FIGURE 39.—Waterplantain (Alisma triviale).

DESCRIPTION.—Waterplantain is an emersed,

erect, aquatic perennial that reproduces by seed

and rootstocks. Plants may grow 48 inches tall.

Leaves are long petioled with elliptical blades

up to 10 inches long and 6 inches wide. The inflorescence is pyramid shaped and branched.

Seeds are round, reddish brown, and about onetenth inch long. Seeds may remain viable in

the soil for many years.

DISTRIBUTION.—Waterplantain is a weed in

rice in California only. It grows in ricefields

where stands are thin, on banks and edges of

irrigation and drainage canals, and in other wet

areas. Seeds of waterplantain germinate under

water and at a lower temperature than rice.

It often grows abundantly where cold water

enters the ricefield.

CONTROL.—Waterplantain may be controlled

by good stands of rice; by allowing the weed

seeds to germinate in water, followed by drainage, drying, and cultivation ; and by herbicides.

It may be killed by spraying with 2,4-D or

MCPA at % to 11/2 pounds per acre. Phenoxy

herbicides should be applied when rice is in the

"tolerant" stage of growth (p. 24).

Waterprimrose

Jussiaea spp.

OTHER NAME.—Primrose-willow.

PRINCIPAL SPECIES AND COMMON NAMES.—

Jiissiaea decurrens (Walt.) DC. (fig. 40) called

winged waterprimrose and /. repens L. var.

glabrescens Ktze. (fig. 41) called creeping

waterprimrose.

DESCRIPTION.—Jussiaea decurrens is an

aquatic annual that reproduces by seed. Stems

are erect, 3 to 6 feet tall, smooth, 4-angled;

leaves are narrow, linear, and sessiled; capsules

are slender, 4-angled, and 1/2 to 1 inch long.

/. reperis var. glabrescens is an aquatic perennial that reproduces by seed, stems, and rootstocks. Stems are smooth, prostrate or ñoating,

ascending at the tips, and rooting at the nodes;

leaves are smooth, oblong, 1 to 4 inches long,

and petioled; capsules are almost cylindrical

and 1 to 2 inches long.

DISTRIBUTION.—Waterprimroses grow mainly in the southern rice-producing areas. They

grow in field bar ditches, irrigation and drainage canals, ditches, and other wet areas. Jussiaea repens var. glabrescens grows in dense

beds in ponds and ditches (fig. 42). Waterprimroses are not generally troublesome in the

rice crop, but they may grow where rice stands

are thin. They compete with rice, interfere

with harvesting and drying, lower rice quality,

and impede now of water in canals and ditches.
m

WEEDS AND THEIR CONTROL IN RICE PRODUCTION

FIGURE 40.—Winged waterprimose (Jussiaea decurrens).

^^^»^

FIGURE 41.—Creeping waterprimrose (Jussiaea repens var. glabrescens).
60 AGR. HANDB. 292, U.S. DEPT. OF AGRICULTURE

CONTROL.—Cultural methods, such as cultivation, good seedbed preparation, good rice

stands, and drainage, are used to control waterprimrose in ricefields. Waterprimroses cannot

be selectively killed in ricefields with herbicides, but they can be controlled in uncultivated

areas. They are susceptible to 2,4-D at 2 to 8

pounds per acre applied in 100 gallons of oil

or water. Oil-carried sprays are more effective

than water-carried ones, which usually require

surfactants.

FIGURE 42.—A creeping waterprimrose bed in a drainage ditch.
WEEDS AND THEIR CONTROL IN RICE PRODUCTION 61

BIBLIOGRAPHY

(1)

(2)

(3)

(4)

(5)

(6)

(7)

(8)

(9)

(10)

(11)

(12)

(13)

(14)

(15)

(16)

(17)

ADAIR, C. R., and ENGLER, KYLE.

1955. THE IRRIGATION AND CULTURE OF RICE.

In Water, U.S. Dept. Agr. Yearbook, pp.

389-394.

AKESSON, N. B., and HARVEY, W. A.

1948. CHEMICAL WEED CONTROL EQUIPMENT.

Calif. Agr. Expt. Sta. Cir. 389, 49 pp.,

illus.

ARAI, M., and MIYAHARA, M.

1962. PHYSIOLOGICAL AND ECOLOGICAL STUDIES

ON BARNYARDGRASS. Crop Sei. Soc.

Japan, Proc. 31(1): 73-77.

and MIYAHARA, M.

1962. PHYSIOLOGICAL AND ECOLOGICAL STUDIES

ON BARNYARDGRASS. Crop Sci. Soc.

Japan, Proc. 31(2): 186-189.

ARKANSAS AGRICULTURAL EXTENSION SERVICE

and UNITED STATES DEPARTMENT OF AGRICULTURE.

1963. RECOMMENDED CHEMICALS FOR WEED AND

BRUSH CONTROL—ARKANSAS 1963. Ark.

Agr. Ext. Serv. Misc. Pub. 44, 16 pp.

(Revised.)

and UNITED STATES DEPARTMENT OF

AGRICULTURE.

1963. TIMING OF NITROGEN FOR RICE—RICE

FERTILIZER RECOMMENDATIONS. Ark. Agr.

Ext. Serv., February, 1 p.

ARKANSAS STATE PLANT BOARD.

1957. OFFICIAL STANDARDS FOR SEED CERTIFICATION IN ARKANSAS. Ark. State Plant

Board Cir. 15, 25 pp. (Revised.)

BAKER, J. B.

1960. AN EXPLANATION FOR THE SELECTIVE CONTROL OF BARNYARDGRASS IN RICE WITH

CIPC. Weeds 8(1): 39-47, illus.

1961. RICE WEED CONTROL. La. Agr. Expt. sta..

Rice Expt. Sta. Ann. Prog. Rpt. 49:

144-150.

HuDGiNS, H. R., and SMITH, R. J., JR.

1962. ECONOMIC DATA ON LOSSES DUE TO WEEDS.

South. Weed Conf. Res. Rpt. 15: 167-168.

BARTON, L. V.

1962. THE GERMINATION OF WEED SEEDS. Weeds

10(3): 174-182.

BEACHER, R. L.

1952. RICE FERTILIZATION. Ark. Agr. Expt.

Sta. Bui. 522, 32 pp.

BINGHAM, S. W., EASLEY, TILDóN, EDWARDS,

F. E., and others.

1958. WEED CONTROL RECOMMENDATIONS. MisS.

Agr. Expt. Sta. Bui. 556, 36 pp., illus.

BOHMONT, D. W.

1953. WEEDS OF WYOMING. Wyo. Agr. Expt.

Sta. Bui. 325, 160 pp., illus.

BRANDES, G. A.

1962. STAM F-34 PROVED SUCCESSFUL FOR GRASS

AND WEED CONTROL IN RICE. Rice Jour.

65(1) : 8, 10, 12, 37-39, illus.

1963. A PROGRESS REPORT OF STAM F-34 FOR

GRASS AND WEED CONTROL IN RICE. Rice

Jour. 66(1) : 6-11, illus.

CAFFEY, H. R., BOWMAN, D. H., and FISHER,

CHARLES.

1962. CHEMICAL CONTROL OF GRASS IN RICE.

Miss. Farm Res. 25(4): 2.

(18)

(19)

(20)

(21)

(22)

(23)

(24)

(25)

(26)

(27)

(28)

(29)

(30)

(31)

(32)

(33)

(34)

CARRIER, LYMAN.

1917. THE IDENTIFICATION OF GRASSES BY THEIR

VEGETATIVE CHARACTERS. U.S. Dept AßT

Dept. Bui. 461, 30 pp., illus.

COLEMAN, P. G., HAYNES, D. W. M., and HITCHCOCK, J. L. B.

1956. OBSERVATIONS ON THE CONTROL OF WEEDS

IN PADI FIELDS BY THE USE OF HERBICIDES.

Malayan Agr. Jour. 39(3): 191-199,

illus.

CRAFTS, A. S.

1961. THE CHEMISTRY AND MODE OF ACTION OF

HERBICIDES. 269 pp., iUus. New York

and London.

DANIELSON, L. L., KLINGMAN, D. L., SHAW,

W. C, and others, compilers.

1961. SUGGESTED GUIDE FOR CHEMICAL CONTROL

OF WEEDS. U.S. Agr. Res. Serv. ARS

22-67, 60 pp.

DAVIS, L. L.

1950. CALIFORNIA RICE PRODUCTION. Calif. Agr.

Ext. Serv. Cir. 163, 56 pp., illus.

DAVIS, W. C.

1954. RESPONSES OF RICE TO SOME HERBICIDES.

Tex. Agr. Expt. Sta. Prog. Rpt. 1678,

4 pp.

1954. WEED INVESTIGATIONS. Rice Tech. Com.

Proc. 6: 19-21.

1955. WEED KILLERS AND RICE. Tex. Agr. Expt.

sta. Prog. Rpt. 1812, 4 pp.

DE LA FUENTE, R. K., FERTIG, S. N., and

LLENA, P. A.

1956. THE EFFECT OF TWO HERBICIDES ON RICE

PLANTS SPRAYED AT DIFFERENT STAGES OF

GROWTH. Philippine Agr. 40(7): 352-

360, illus.

DREESSEN, JACK.

1959. PESTICIDE LAW MANUAL. Nati. Agr.

Chem. Assoc. Washington, D. C.

DUNHAM, R. S.

1961. HERBICIDE MANUAL FOR MILITARY INSTALLATIONS. U.S. Dept. of the Navy, 141 pp.

DUNSHEE, C. F.

1928. RICE EXPERIMENTS IN SACRAMENTO VALLEY

1922-1927. Calif. Agr. Expt. Sta. Bui.

454, 16 pp., illus.

EDWARDS, F. E.

1957. SPRAYERS FOR WEED CONTROL IMPROVED.

Miss. Farm Res. 20(4) : 7, illus.

ENNIS, W. B., JR.

1958. THE CHALLENGES OF MODERN WEED CONTROL. Weeds 6(4): 363-369.

FERNALD, M. L.

1950. GRAY'S MANUAL OF BOTANY. 1632 pp.,

illus. New York.

FINFROCK, D. C, VISTE, K. L., HARVEY, W. A.,

and MILLER, M. D. J, K TP ^

1958. WEED CONTROL IN RICE. Calif. Agr. bxt.

Serv. Leaflet 97, 2 pp. illus.

FRENCH, G. W., and GAY, W. B.

1963. WEED CONTROL IN RICE FIELDS. Worm

Crops 15(5): 196-199, 201-204, 206,

illus.
62 AGR. HANDB. 292, U.S. DEPT. OF AGRICULTURE

(35)

(36)

(37)

(38)

(39)

(40)

(41)

(42)

(43)

(44)

(45)

(46)

(47)

(48)

(49)

(50)

(51)

(52)

GARD, L. N., and RUDD, G.

1953. HERBICIDE DETERMINATION: ISOPROPYL

N-(3-CHLOROPHENY) CARBAMATE (CIPC)

IN SOIL AND CROPS. Jour. Agr. and Food

Chem. 1: 630-632.

GLEASON, H. A.

1952. THE NEW BRITTON AND BROWN ILLUSTRATED FLORA or THE NORTHEASTERN

UNITED STATES AND ADJACENT CANADA.

3 v., illus. Lancaster, Pa.

GRIST, D. H.

1959. RICE. Ed. 3, 466 pp., illus. New York.

HALL, VERNON, BRYAN, BILLY, ENGLER, KYLE,

and others.

1963. PLASTIC LEVEES IN RICE IRRRIGATION.

Ark. Farm Res. 12(1): 4, illus.

HARDCASTLE, W. S.

1962. AQUATIC WEEDS. South. Weed Conf. Res.

Rpt. 15: 115-126.

HEIKES, P. E.

1959. WEED CONTROL EQUIPMENT. Mont. State

Col. Ext. Bui. 300, 24 pp., illus.

HITCHCOCK, A. S.

1950. MANUAL OF THE GRASSES OF THE UNITED

STATES. Ed. 2, 1051 pp., illus. Washington, D. C.

HODGES, R. J.

1962. CONTROL OF GRASS AND WEEDS IN RICE.

Tex. Agr. Ext. Serv. Rice Notes and

Quotes 5(8): 1-2.

HUDGINS, H. R.

1961. CHEMICAL CONTROL OF BARNYARDGRASS IN

THE TEXAS RICE BELT. South. Weed Conf.

Proc. 14: 107-110.

1962. CONTROL OF BARNYARDGRASS IN RICE WITH

DPA. Tex. Agr. Expt. Sta. Prog. Rpt.

2229, 4 pp.

JOHNSON, F. S.

1952. REPORT ON PRELIMINARY INVESTIGATION

ON CHEMICAL WEED CONTROL IN VENEZUELA 1951. Internatl. Basic Econ. Corp.

Res. Inst. Rpt. 2, 20 pp., illus.

JOHNSTON, T. H., CRALLEY, E. M., and HENRY,

S. E.

1959. PERFORMANCE OF RICE VARIETIES IN ARKANSAS, 1953-1958. Ark Agr. Expt. Sta.

Rpt. Ser. 85, 31 pp.

JONES, J. W.

1926. EXPERIMENTS IN RICE CULTURE AT THE

BIGGS RICE FIELD STATION IN CALIFORNIA.

U.S. Dept. Agr. Dept. Bui. 1387, 39 pp.,

illus.

1933. EFFECT OF DEPTH OF SUBMERGENCE ON

THE CONTROL OF BARNYARDGRASS AND

YIELD OF RICE GROWN IN POTS. Amer.

Soc. Agron. Jour. 25(9): 578-583.

DAVIS, L. L., and WILLIAMS, A. H.

1950. RICE CULTURE IN CALIFORNIA. U.S. Dept.

Agr. Farmers' Bui. 2022, 32 pp., illus.

DocKiNS, J. 0., WALKER, R. K., and

DAVIS, W. C.

1952. RICE PRODUCTION IN THE SOUTHERN

STATES. U.S. Dept. Agr. Farmers' Bui.

2043, 36 pp., illus.

KAPP, L. C, and BARTHOLOMEW, R. P.

1947. THE EFFECT OF CONTROLLING WEEDS BY

IRRIGATION AND SEEDING PRACTICES ON

RICE YIELDS. Ark. Agr. Expt. Sta. Bui.

467, 7 pp.

KAUFMAN, P. B.

1953. GROSS MORPHOLOGICAL RESPONSES OF THE

RICE PLANT TO 2,4-D. Weeds 2 (4) : 223-

255, illus.

(53)

(54)

(55)

(56)

(57)

(58)

(59)

(60)

(61)

(62)

(63)

(64)

(65)

(66)

(67)

(68)

(69)

(70)

1955. HISTOLOGICAL RESPONSES OF THE RICE

PLANT (oRYZA SATIVA) TO 2,4-D. Amer.

Jour. Bot. 42(7): 649-659, illus.

and CRAFTS, A. S.

1956. RESPONSE OF THE RICE PLANT TO DIFFERENT FORMULATIONS AND METHODS OF

APPLICATION OF 2,4-D, MCPA, AND 2,4,5-T,

Hilgardia 24: 411-453, illus.

KLINGMAN, D. L., and SHAW, W. C.

1962. USING PHENOXY HERBICIDES EFFECTIVELY.

U.S. Dept. Agr. Farmers' Bui. 2183, 24

pp., illus.

KLINGMAN, G. C.

1961. WEED CONTROL: AS A SCIENCE. 421 pp.,

illus. New York and London.

LEWIS, D. C, SCOTT, V. H., MUELLER, K. E., and

others.

1962. NEW RICE LEVEE CONCEPTS. Rice Jour.

65(4) : 6-15, illus.

MCRAE, D. H., WILSON, H. F., and SATTERTHWAITE, S. T.

1961. THE RESPONSE OF RICE AND WEEDS TO

3',4'-DICHLOROPR0PI0NANILIDE AND TO RELATED ANILIDES. South. Weed Conf. Proc.

14: 321-324.

MARTIN, A. C, ERICKSON, R. C, and STENNIS,

J. H.

1957. IMPROVING DUCK MARSHES BY WEED CONTROL. U.S. Fish and Wildlife Serv. Cir.

19, 60 pp., illus. (Revised.)

MATSUBAYASHI, M., ITO, R., NOMOTO, T.,

TAKASE, T., and YAMADA, N., compilers.

1963. THEORY AND PRACTICE OF GROWING RICE.

502 pp., illus. Tokyo.

MEYER, B. S., and ANDERSON, D. B.

1939. UTILIZATION OP MINERAL SALTS. In

Plant Physiology, pp. 415-436, illus. New

York.

MILLIGAN, TOM.

1957. TWICE THE RICE AT A PRACTICAL PRICE.

Farm and Ranch 87(4) : 20, illus.

NEFF, J. A., and MEANLEY, BROOKE.

1957. BLACKBIRDS AND THE ARKANSAS RICE

CROP. Ark. Agr. Expt. Sta. Bui. 584,

89 pp., illus.

NELSON, MARTIN.

1944. ROTATION, CULTURAL, AND IRRIGATION

PRACTICES AFFECTING RICE PRODUCTION.

Ark. Agr. Expt. Sta. Bui. 445, 45 pp.

NESTER, R. P.

1962. FOR MORE RICE PROFIT CONTROL BARNYARDGRASS. Ark. Agr. Ext. Serv. Leaflet 288,

8 pp., illus. (Revised.)

1963. STAGES OF DEVELOPMENT OF RICE VARIETIES IN ARKANSAS. Rice Jour. 66(3):

31-32.

1964. RICE PRODUCTION IN ARKANSAS. Ark.

Agr. Ext. Serv. Cir. 476, 35 pp. (Revised.)

ODGLEN, G. E., and WARREN, L. 0.

1962. THE RICE STINK BUG, OEBALUS PUGNAX

F., IN ARKANSAS. Ark. Agr. Expt. Sta.

Rpt. Ser. 107, 24 pp., illus.

OLSEN, K. L.

1957. "SCUM" CONTROL IN RICE FIELDS AND IRRIGATION CANALS. Ark. Agr. Expt. Sta.

Rpt. Ser. 69, 20 pp., illus.

ORSENIGO, J. R.

1956. RICE INVESTIGATIONS IN VENEZUELA IN

1954. Internatl. Basic Econ. Corp. Res.

Inst. Rpt. 8, 28 pp., illus.
WEEDS AND THEIR CONTROL IN RICE PRODUCTION 63

(71)

(72)

(73)

(74)

(75)

(76)

(77)

(78)

(79)

(80)

(81)

(82)

(83)

(84)

(85)

(86)

(87)

PHILLIPS, P. J., and JUDD, MORROW.

1963. AN EVALUATION OF HIGH VISCOSITY,

CROWDED PHASE EMULSIONS AS HERBICIDE

CARRIERS WHEN APPLIED THROUGH THE

BIFLUID SPRAY SYSTEM. Southwest Agr.

Inst. Prog. Rpt. Sp-7b, 88 pp., illus.

PRINCE, A. H.

1927. WEEDS AND GRASSES IN ARKANSAS RICE

FIELDS. Ark. Agr. Ext. Serv. Cir. 253,

12 pp., illus.

RoBBiNS, W. W., CRAFTS, A. S., and RAYNOR,

R. N.

1952. WEED CONTROL. 503 pp., illus. New York

and London.

ROHM AND HAAS CO.

1963. STAM F-34 AERIAL APPLICATION MANUAL

FOR GRASS AND WEED CONTROL IN RICE.

Ag-172a, 10 pp., illus. Philadelphia.

1963. STAM F-34 FOR GRASS AND WEED CONTROL

IN RICE. Ag-190, 16 pp., illus. Philadelphia.

1964. STAM i^34. EX-A-73, 8 pp. Philadelphia.

SCOTT, V. H., LEWIS, D. C, FOX, D. R., and

BABB, A. F.

1961. PLASTIC LEVEES FOR RICE IRRIGATION.

Calif. Agr. 15(11) : 8-9.

SEAMAN, D. E., BLACKBURN, R. D., and WELDON, L. W.

1961. SUGGESTED CONTROL MEASURES FOR COMMON AQUATIC WEEDS OF FLORIDA. U.S.

Agr. Res. Serv., Crops Res. Div. Prog.

Rpt. 42-61, 10 pp.

SHAW, W. C.

1963. RECENT TECHNOLOGICAL ADVANCES IN

WEED CONTROL. Rice Tech. Working

Group Proc, Feb. 1962, 10: 12-14.

1964. WEED SCIENCE—REVOLUTION IN AGRICULTURAL TECHNOLOGY. Weeds 12(3): 153-

162.

ALLEN, W. W., ASHTON, F. M., and

others.

1962. REPORT OF THE TERMINOLOGY COMMITTEE,

WEED SOCIETY OF AMERICA. Weeds 10(3) :

255-271.

SIERRA, J. N.

1957. EFFECTS OF HERBICIDES ON WEED SPECIES

IN LOWLAND AND UPLAND RICE FIELDS.

Philippine Agr. 41(3) : 171-190.

SLIFE, F. W., BUCHHOLTZ, K. P., and KOMMEDAHL, T.

1960. WEEDS OF THE NORTH CENTRAL STATES.

111. Agr. Expt. Sta. Cir. 718, 262 pp.,

illus.

SMALL, J. K.

1933. MANUAL OF THE SOUTHEASTERN FLORA.

1554 pp., illus. Chapel Hill, N. C.

SMITH, R. J., JR.

1956. WEED CONTROL IN RICE IN THE SOUTHERN

UNITED STATES. Rice Tech. Working

Group Proc. 7: 18-20.

1958. THE DIFFERENTIAL VARIETAL RESPONSES

OF RICE TO 2,4-D AS INFLUENCED BY THE

STAGE OF GROWTH AND RATE OF APPLICATION. Rice Jour. 61(10): 18-19, 26-27,

illus.

1960. CHEMICAL CONTROL OF BARNYARDGRASS IN

RICE. Weeds 8(2): 256-267, illus.

(88)

(89)

(90)

(91)

(92)

(93)

(94)

(95)

(96)

(97)

(98)

(99)

(100)

(101)

1960. EFFECT OF LOW RATES OF SEVERAL PHENOXYALKYLCARBOXYLICACIDSON SOYBEANS

South. Weed Conf. Proc. 13: 243-244.

1960. EFFECT OF POST-EMERGENCE APPLICATIONS

OF SEVERAL PHENOXYCARBOXYLIC ACIDS ON

RICE. (Abstract) Weed Soc. Amer., pp.

5-6.

1960. NITROGEN MANAGEMENT IN RICE INFESTED

WITH BARNYARDGRASS. Ark. Farm Res.

9(1): 2, illus.

1960. 3,4-DICHLOROPROPIONANILIDE: A PROMISING NEW HERBICIDE FOR CONTROL OF

BARNYARDGRASS IN RICE. South. Weed.

Conf. Proc. 13: 245-247.

1961. CONTROLLING BARNYARDGRASS IN RICE

WITH 3,4-DICHLOROPROPIONANILIDE. South.

Weed. Conf. Proc. 14. 104-106.

1961. 3,-4-DICHLOROPROPIONANILIDE FOR CONTROL

OF BARNYARDGRASS IN RICE. Weeds 9(2) :

318-322, illus.

1962. WEED INVESTIGATIONS IN RICE.

Jour. 65(7) : 42-44.

Rice

(102)

(103)

(104)

(105)

1963. CONTROL OF BROADLEAVED WEEDS AND

WEED GRASSES IN RICE. Rice Tech. Working Group Proc, Feb. 1962, 10: 11-12.

BAKER, J. B., and HUDGINS, H. R.

1962. WEEDS IN RICE. South. Weed Conf. Res.

Rpt. 15: 48-51.

and ENNIS, W. B., JR.

1953. STUDIES ON THE DOWNWARD MOVEMENT

OF 2,4-D, AND 3-CHLORO-IPC IN SOILS.

South. Weed Conf. Proc. 6: 63-71.

VISTE, K. L., and SHAW, W. C.

1959. PROGRESS IN WEED CONTROL IN RICE PRODUCTION IN THE UNITED STATES. Internatl. Rice Comn. News Letter 8(3) : 1-6.

STAUFFER CHEMICAL CO.

1964. WEED CONTROL IN RICE IN CALIFORNIA.

24 pp.

STEVENS, J. D. H.

1962. MISSISSIPPI GROWERS REPORT PROGRESS.

Rice Jour. 65(10) : 21-24, illus.

TAKEMATSU, T., and YANAGISHIMA, S.

1963. STUDIES ON THE HERBICIDAL PHENOMENON

AND THE FUNCTION OF DICHLOROPROPIONANILIDE A WEED KILLER HAVING A

SELECTIVE HERBICIDAL EFFECT ON GENERA

OF GRAMINEAE. II Riso (12(3): 37-70,

illus.

U.S. AGRICULTURAL RESEARCH SERVICE.

1962. ESTIMATED LOSSES CAUSED BY WEEDS IN

AGRONOMIC CROPS—AVERAGES, 1951-1960.

U.S. Agr. Res. Serv., Crops Res. Div.,

May, 1 p.

1962. SUMMARY OF REGISTERED AGRICULTURAL

PESTICIDE CHEMICAL USES. U.S. Agr. Res.

Serv., Pesticides Régulât. Div., Washington, D. C, 686 pp.

VELASCO, J. R., VEGA, M. R., and LLENA, F. A.

1958. EFFECTS OF REPEATED HERBICIDE SPRAYING

ON UPLAND RICE. Philippine Agr. 41(8) :

432-439.

VISTE, K. L.

1963. CONTROL OF WEEDS IN RICE IN CALIFORNIA.

Rice Tech. Working Group Proc, heb.

1962, Houston, Tex., pp. 10-11.
64 AGR. HANDB. 292, U.S. DEPT. OF AGRICULTURE

(106) VISTE, K. L. and FINFROCK, D. C. (109)

1958. FACTORS INFLUENCING HERBICIDAL INJURY

TO RICE. Rice Tech. Working Group Proc.

8: 9-12, illus.

(107) WARD, J. C. (HO)

1960. REGISTRATION OF HERBICIDES—STATUS,

PROBLEMS, PLANS. Weed Soc. Amer.

Spec. Panel Discuss, on Prog, and Prob,

in Registering and Recommending Herbicides, pp. 6-10. (Ill)

(108) WELLHAUSEN, H. W.

1955. RICE PRODUCTION IN ARKANSAS. ARK.

Agr. Ext. Serv. Cir. 476, 12 pp., illus.

WELLS, J. P.

1963. RICE FERTILITY RESEARCH IN ARKANSAS.

Rice Tech. Working Group Proc, Feb.

1962, 10:9.

WILLIAMS, R. E.

1955 and 1956. WEEDS IN RICE. Rice Jour. 58

(13): 18-19; 59(1): 8-9; (2): 8; (3):

8-9; (4): 14; (5): 24; (6): 34-35; (8):

22-23; (9): 15; (10): 16-17; (12): 20-

28.

WooTEN, O. B., and HOLSTUN, J. T., JR.

1959. SPECIAL EQUIPMENT FOR CHEMICAL WEED

CONTROL. Miss. Agr. Expt. Sta. Bui.

576, 16 pp., illus.

APPENDIX

TABLE 22.—Covtmon and chemical names of herbicides reported in handbook

Common name Chemical name

amitrole 3-amino-l,2,4-triazole

amitrole-T 3-amino-l,2,4-triazole-ammonium thiocyanate mixture

CIPC isopropyl A/-(3-chlorophenyl)carbamate

dalapon 2,2-dichloropropionic acid

EPTC ethyl N'.N'-di-propylthiolcarbamate

MCPA 2-methyl-4-chlorophenoxyacetic acid

molinate S-ethyl hexahydro-1 íí-azepine-1-carbothioate

propanil 3',4'-dichloropropionaniHde

silvex 2-(2,4,5-trichlorophenoxy)propionicacid

swep methyl 3,4-dichlorocarbanilate

2,4-D___ 2,4-dichlorophenoxyacetic acid

2,4,5-T 2,4,5-trichlorophenoxyacetic acid

4-chlorobenzenesulfono-2-toluidide

ADDENDUM

Molinate has been cleared by the U.S. Department of Agriculture for

controlling weeds in rice. It may be applied at 3 pounds per acre as a

preplanting application on water-seeded rice, but may not be applied to

dry-seeded rice. It is effective in controlling grass weeds when it is

incorporated into the soil before flooding and seeding rice.

¡¡ï U.S. GOVERNMENT PRINTING OFFICE: 1966—783-24S