United States

Department of

Agriculture

Forest Service Research Note

Southern Forest

Experiment Station

SO-381

September 1995

Controlling Herbaceous Competition in Pasture

Planted with Loblolly Pine Seedlings

James D. Haywood

Three treatments designed to control herbaceous vegetation competing with loblolly pine (Pinus taeda L.) seedlings planted in grazed and ungrazed pasture were tested.

Effects of the treatments on seedling survival and growth

during the first 3 years after planting were determined.

The treatments were directed application of herbicides

(glyphosate in the first 2 years and hexazinone in the

third year), rotary mowing, and mulching with pine straw

around individual pine seedlings.

After 3 years, the herbicide and mulching treatments

increased the groundline diameter and total height of

loblolly pine seedlings. Grazing apparently reduced pine

survival and height growth. However, the observed treatment effects are not sufficient basis for a recommendation that a particular cultural practice be applied.

Landowners who want to continue grazing cattle as pastures convert to pine will have to accept a reduction in

pine survival and less seedling height growth.

INTRODUCTION

Many pastures and idle fields in loblolly pine (Pinus

taeda L.), shortleaf pine (P echinata Mill.), and hardwood

forest areas of the Southern United States are being

planted to pines (Yeiser and others 1987). Herbaceous

vegetation on pastures and idle fields can impede the

establishment and growth of pine seedlings by competing with the pine seedlings for water and nutrients (Bacon and Zedaker 1987, Haywood 1994, Tiarks and

Haywood 1986, Zutter and others 1986). Several herbicides are labeled for controlling herbaceous vegetation

in pine plantings. Mowing is an alternative that may appeal to landowners who already have the necessary

equipment (Schmidtling 1984).

The use of tractors to apply herbicides and mow in

pine plantations presents difficulties: planting spacings

must be based on mechanical constraints, terrain is a

factor, late winter and spring rains can cause unstable

soil conditions that interfere with operations, and soils

may be compacted (Yeiser and others 1987). It is possible that applying mulch around the seedlings at the

time of planting would prevent these problems. Although

mulching is labor intensive, it may be practical where

landowners with limited budgets are converting pasture

or idle fields to pines. Farmers all around the world use

mulches and crop residues to control weeds in field and

horticultural crops, but mulches and crop residues are

used less often in forestry (Buller and Gibbs 1952, Dao

1987, Gale and others 1993, Ghadiri and others 1984,

Gupta 1991, Mahajan and Kanwar 1993, Mayhead 1992,

McDonald and Helgerson 1990, Sanderson and Cutcliffe

1991, Schroth and others 1992, Shekour and others

1987, Sood and Sharma 1985, Walker and McLaughlin

1989, Zuzel and Pikul 1993).

An experiment was performed to determine the effects

of various competition-control treatments on the survival

and growth of planted loblolly pine seedlings in grazed

and ungrazed pastures. Only effects during the first 3

years after planting were considered, because loblolly

pines are large enough to tolerate cattle pressure after 3

years. It was assumed that rural property owners would

have access to agricultural chemicals, tractors, mowers,

or a supply of pine mulch, and that most owners would

select one technique for managing vegetation rather than

a combination of the three techniques evaluated in this

study.

METHODS

The field work was done in central Louisiana. The study

area was located within a direct-seeded slash pine

(t? elliottii Engelm. var elliottii) stand on a BeauregardSouthern Forest Experiment Station/T-l0210 U.S. Postal Services Bldg., 701 Loyola Avenue, New Orleans, La. 70113

Forest Service, U.S; Department of Agricultirre.

Serving Alabama, Arkansas, Louisiana, Mississippi, E. Oklahoma, Tennessee, E. Texas, Puerto Rico, U.S. Virgin Islands.
Guyton association, of deep, medium textured, and slowly

permeable soils. In October 1980, a 1 O-acre area within

the slash pine stand was clearcut harvested, stumped,

burned to remove woody debris, disked, and then treated

with 1,620 lb/acre of dolomitic limestone, 4.5 lb/acre of

sulphur, 36 lb/acre of phosphorus (as P,O,), and 68 lb/

acre of potassium (as K,O) (Pearson and Baldwin 1993).

A cattle management program was begun, and this included yearly top dressing with 21 lb/acre of phosphorus (as P,O,) and 39 lb/acre of potassium (as &O), cattle

grazing, and applications of glyphosate herbicide.

In January 1991, the original cattle management study

ceased, and five areas within the 1 O-acre site were selected as blocks for this experimental work. The five

blocks were all in open pasture.Three of the blocks were

fenced to exclude cattle, and grazing continued on the

other two. The five blocks were as follows:

(1) Ungrazed Kentucky fescue-Kentucky31 fescue

(Festuca arundinacea Schreb.) and Florida

bahiagrass (Paspalum notatum Flugge) were the

primary grasses.

(2) Ungrazed ryegrass and clover-Gulf Coast

ryegrass (Lolium perenne L.) and seeded Mt.

Barker or Woogenellup subterranean clover (7%

folium subterraneum L.) .

(3) Ungrazed ryegrass only.

(4) Grazed ryegrass that had been disked in 1990.

(5) Grazed subterranean clover that had been

disked in 1990.

Cattle were grazed in blocks 4 and 5 after January

1991. Otherwise, no effort was made to maintain the

pasture vegetation present at the beginning of the study.

A randomized complete block design was employed.

There were four treatment plots in each of the five blocks.

In January 1991, each 64- by 64-ft plot was planted with

sixty-four 28-week-old container grown loblolly pine seedlings spaced 8 by 8 ft apart. The seedlings were of uniform quality and size at planting.

Each of the following four treatments was randomly

assigned to one plot in each block:

(1) Check: No more cultural treatments.

(2) Herbicides’: A l-percent solution of glyphosate

in water was applied as a directed spray in April

1991 and April 1992, and the seedlings were

shielded during both applications. In April 1993,

hexazinone was broadcast at the rate of 1 lb

active ingredient/acre.

‘The chemical names of the herbicides are as follows: glyphosate

(Njphosphonomethyl] glycine) as Roundupe and hexazinone (3-

cyclohexyl-6-[dimethylaminol-1 -methyl-l, 3, 5-triazine-2, 4 [l H, 3H]-

dione) as Velpar%

(3) Rotary mowing: The plots were rotary mowed

three times each growing season from 1991

through 1993.

(4) Mulching: In April 1991, 11 lb of air-dried (moisture content about 15 percent) pine straw (principally /?pa/ustris Mill.) was placed around each

seedling. Up to 5 lb of air-dried pine straw was

added to individual seedlings in 1992 if needed

to control weeds.

Because cattle grazing was still practical in these pastures, neither rotary mowing nor use of herbicide was

intended to eliminate the nonpine vegetation. Rather,

mowing and herbicide applications were meant to keep

established pasture vegetation from overtopping and

suppressing the pine seedlings. Glyphosate was used

to determine whether control of the established cover

followed by revegetation from seed would be sufficient

to stimulate young pine growth. Hexazinone provides

longer residual control than glyphosate does, and the

seedlings were large enough by the third year in the field

to tolerate hexazinone. The loblolly pine seedlings were

not visibly injured by the herbicide treatments.

The central 16 pine seedlings on each plot served as

the measurement trees. After the first growing season,

herbaceous plant standing crop was determined by clipping and weighing the aboveground biomass in eight

randomly selected 1 V-acre subplots within each study

plot. Nonpine plants were inventoried and heights and

groundline diameters of the loblolly pine seedlings were

measured after three growing seasons.

Analysis of variance (alpha=0.05) was used to determine whether there were any significant treatment effects on herbaceous standing crop or loblolly pine

survival, total height, and groundline diameter. Where

treatment effects were significant, Duncan’s Multiple

RangeTests were used to separate the treatment means.

RESULTS AND DISCUSSION

Treatments that could be employed on small landholdings were used to convert grazed and abandoned pastures to planted pine. Owners of rural property may have

access to agricultural chemicals, tractors and rotary

mowers, or straw mulch. Each cultural practice has its

own set of associated problems, but none of the treatments tested presents exceptional difficulties. Block effects are discussed because the effects of grazing on

pine survival and growth are a concern to landowners

who would like to graze cattle on lands they have planted

to pine.

James D. Haywood is a silviculturist at the Alexandria Forestry Center, U.S. Department of Agriculture, Forest Service, Southern Forest Experiment Station, Pineville, LA 71360.

2
Loblolly Pine

Loblolly pine survival was not significantly affected by

treatment, but survival was slightly lower when herbicides

were used (table 1). Damage caused by cattle killed some

pine seedlings, and pine survival averaged 70 percent

on the two grazed blocks and 83 percent on the three

ungrazed blocks after three growing seasons. However,

the difference between survival in the grazed and

ungrazed blocks did not seem great enough to justify

excluding cattle from planted areas.

Groundline diameters of 3-year-old loblolly pines that

received herbicide treatments were greater than those

of 3-year-old loblolly pines in the check and rotary mowing plots (table 1). Loblolly pines that were mulched were

significantly taller than those on the check and rotary

mowing plots. Groundline diameters and total heights of

pines that were mulched were comparable to those of

pines that received herbicide treatments.

Grazing apparently did not affect the groundline diameter of the loblolly pines. Pine diameter averaged 2.0 in

on the grazed blocks and 2.2 in on the ungrazed blocks

(table 1). However, cattle broke the leaders of some trees

and bent some trees over. As a result, pines in the grazed

blocks averaged 4.9 ft tall and those in the ungrazed

blocks averaged 8.3 ft tall.

Herbaceous Standing Crop

After one growing season, herbaceous plant production was not significantly affected by treatment (table 1).

Rotary mowing produced the least herbage. The rotary

mowing plots were cut three times each year, so rotary

mowing affected standing crop much as grazing did. After the first growing season, herbaceous production averaged 938 lb/acre in the grazed blocks and 1,804 lb/

acre in the ungrazed blocks. The pine straw mulch was

placed around individual seedlings, so mulching did not

influence herbaceous production in all areas of the

mulched plot. Glyphosate controlled the herbaceous

vegetation initially, but new vegetation developed by the

time the herbaceous samples were collected.

Grazing and cultural treatments influenced which plant

species were most common on the plots. Three years

after grazing ceased in the Kentucky fescue pasture,

mowing and herbicide applications increased Florida

bahiagrass cover and reduced Kentucky fescue cover.

In the ungrazed ryegrass and clover pasture, blackberry

(Rubus spp.) was the most common plant on the check

and mulched plots. The use of herbicides resulted in the

replacement of ryegrass and clover by hairy crabgrass,

Digitaria sanguinalis (L.) Stop.; blue waxweed, Cuphea

carthagensis (Jacq.) Macbr.; and dogfennel, Eupatorium

capillifolium (Lam.) Small, whereas mowing increased

Florida bahiagrass; vasseygrass, Paspalum urvillei

Steud.; and common carpetgrass, Axonopus affinis

Chase. The ungrazed ryegrass pasture became dominated by common carpetgrass regardless of treatment.

The check and herbicide plots in the grazed and disked

ryegrass pasture were dominated by dogfennel, common carpetgrass, and vasseygrass, but dogfennel was

uncommon in the mowed and mulched plots. Blackberry

dominated the check and mulched plots in the grazed

and disked clover pasture. On the mowing plot, the most

Table 1 .-Survival, groundline diameter and height of 3-year-oldloblollypines (Pinus taeda L.) planted

in pasture and the herbaceous p/ant standing crop production after the first growing season

Treatments

and blocks Survival

Loblolly pine

Groundline

diameter

Total

height

Competing

plant

biomass

Treatments

Check

Herbicides

Rotary mowing

Mulching

78a*

70a

81a

83a

Mean 7 8

Blocks

Ungrazed Kentucky fescue

Ungrazed ryegrass and clover

Ungrazed ryegrass

Grazed and disked ryegrass

Grazed and disked clover

Mean

Percent Inches Feet Lb/acre

8 6 1.7 7.0 2,677

7 3 2.5 9.1 1,106

9 1 2.4 8.7 1,629

7 8 1.8 4.5 1,096

6 1 2.1 5.3 780

7 8 2.1 6.9 1,458

1.8b

2.4a

2.0b

2.2ab

2.1

6.4b

7.2ab

6.4b

7.6a

6.9

1,900a

1,397a

773a

1,760a

1,458

‘Treatment means within columns followed by the same letter are not significantly different based

on Duncan’s Multiple RangeTest (alpha=0.05).
common plant was Florida bahiagrass. On the herbicide

plot, blue waxweed, hairy crabgrass, and dogfennel were

most common.

CONCLUSIONS

Loblolly pine growth differed among treatments, but

the range in treatment responses did not justify a recommendation that herbicides, rotary mowing, or mulching treatments be applied to increase seedling growth

during the critical early years after planting. Other herbicides or treatments not used in this research might be

more effective in controlling competitors. For example,

postplanting weed control with soil active herbicides in the

first and second growing seasons or disking might give good

results (Haywood 1994). However, cattle grazing would have

to be curtailed if the forage were almost eliminated.

Damage caused by cattle killed some loblolly pine

seedlings and reduced the height growth of other seedlings over the 3-year period. The 13-percent reduction in

survival and 3-ft loss in height growth would have to be

acceptable costs to landowners who want to continue

grazing cattle as pastures convert to pine.

LITERATURE CITED

Bacon, Catherine G.; Zedaker, Shepard M. 1987.

Third-year growth response of loblolly pine to eight

levels of competition control. Southern Journal of Applied Forestry. 11: 91-95.

Buller, George B.; Gibbs, J.A. 1952. Planted loblolly pines

respond to mulching. Journal of Forestry. 50: 317318.

Dao, Thanh H. 1987. Crop residues and management of

annual grass weeds in continuous no-till wheat (Triticum

aestivum). Weed Science. 35: 395-400.

Gale, William J.; McCall, R.W.; Fang, Xie. 1993. Sandy

fields traditional farming for water conservation in

China. Journal of Soil and Water Conservation. 48:

474-477.

Ghadiri, Hossein; Shea, Patrick J.; Wicks, Gail A. 1984.

Interception and retention of atrazine by wheat (Triticum

aestivum) stubble. Weed Science. 32: 24-27.

Gupta, G.N. 1991. Effects of mulching and fertilizer application on initial development of some tree species.

Forest Ecology and Management. 44: 211-221.

Haywood, James D. 1994. Tenth-year results of herbaceous weed control in a loblolly pine plantation. Southern Journal of Applied Forestry. 18: 105-l 09.

Mahajan, K.K.; Kanwar, B.B. 1993. Effect of pine (Pinus

species)-needle mulch on maize (Zea mays)-wheat

(Trticum aestivum) cropping system. Indian Journal

of Agronomy. 38: 515518.

Mayhead, G.J. 1992. Some alternatives to herbicides in

British forestry. Quarterly Journal of Forestry. 86: 105-

112.

McDonald, Philip M.; Helgerson, Ole T. 1990. Mulches

aid in regenerating California and Oregon forests: past,

present, and future. Gen. Tech. Rep. PSW-123. Berkeley, CA: US. Department of Agriculture, Forest Service, Pacific Southwest Research Station. 19 p.

Pearson, H.A.; Baldwin, V.C. 1993. Agroforestry: southern pines and subterranean clover cultural treatments.

Agroforestry Systems. 22: 49-58.

Sanderson, K.R.; Cutcliffe, J.A. 1991. Effect of sawdust

mulch on yields of select clones of lowbush blueberry.

Canadian Journal of Plant Science. 71: 1263-1266.

Schmidtling, R.C. 1984. Early intensive culture affects

long-term growth of loblolly pine trees. Forest Science.

30: 491-498.

Schroth, Gotz; Zech, Wolfgang; Heimann, Gunter. 1992.

Mulch decomposition under agroforestry conditions in

a sub-humid tropical savanna processes and influence

of perennial plants. Plant and Soil.147: l-l 1.

Shekour, G.M.; Brathwaite, R.A.I.; McDavid, C.R. 1987.

Dry season sweet corn response to mulching and

antitranspirants. Agronomy Journal. 79: 629-631.

Sood, MC.; Sharma, R.C. 1985. Effect of pine needle

mulch on tuber yield and fertilizer economy of potato

in Simla Hill soil. Journal of the Indian Society of Soil

Science. 33: 141-l 44.

Tiarks, Allan E.; Haywood, James D. 1986. Pinus taeda

L. response to fertilization, herbaceous plant control,

and woody plant control. Forest Ecology and Management. 14: 103-l 12.

Walker, R.F.; McLaughlin, S.B. 1989. Black polyethylene

mulch improves growth of plantation-grown loblolly pine

and yellow-poplar. New Forests. 3: 265-274.

Yeiser, J.L.; Sundell, E.; Boyd, J.W. 1987. Preplant and

postplant treatments for weed control in newly planted

pine. Bulletin 902. Fayetteville, AK: Arkansas Agriculture Experiment Station, University of Arkansas Division of Agriculture. 10 p.

Zutter, B.R.; Glover, G.R.; Gjerstad, D.H. 1986. Effects

of herbaceous weed control using herbicides on a young

loblolly pine plantation. Forest Science. 32: 882-899.

Zuzel, John F.; Pikul, J.L., Jr. 1993. Effects of straw mulch

on runoff and erosion from small agricultural plots in

northeastern Oregon. Soil Science. 156: 11 l-l 17.

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This publication reports research involving pesticides. It does not contain

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CAUTION: Pesticides can be injurious to humans, domestic animals, desirable plants, and fish or other wildlife-if they are not handled or applied properly Use all herbicides selectively and carefully. Follow recommended practices

for the disposal of surplus pesticides and their containers.

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