Combinations of Foliar- and Soil-Applied Herbicides

For Controlling Hardwood Brush

JAMES D. HAYWOOD

SUMMARY

Triclopyr and 2,4,5-T esters at 1.0 lb a/A; and

hexazinone, picloram, and tebuthiuron pellets at 3.0

lb a/A were applied either separately or in liquid and

pellet herbicide combinations to l/60-acre plots for

mixed hardwood brush control. Only two treatments

-triclopyr ester with picloram pellets and 2,4,5-T

ester with picloram pellets - gave acceptable topkill

of mixed brush through two growing seasons.

Additional keywords: 2,4,5-T ester, triclopyr

ester, picloram, tebuthiuron, hexazinone.

percent or better control of mixed hardwood brush in

central Louisiana at a 6 lb a/A rate, while 2,4,5-T at 2

lb a/A is generally accepted as an effective rate.

Lesser rates have been unsatisfactory. In this study,

the pellet herbicides (hexazinone, picloram, and

tebuthiuron)s were broadcast at a 3.0 lb a/A rate,

and the liquid herbicides (2,4,5-T and triclopyr) were

sprayed at a 1 .O lb a/A rate.

INTRODUCTION

Reducing herbicide application rates would lower

capital investment costs and reduce environmental

risks in forest management. But it is difficult to control

the numerous hardwood species with low dosages of

a single herbicide. Herbicide combinations are one

means of increasing the spectrum of weeds controlled without increasing the dosages used.

The herbicides were tested singly and in liquidpellet combinations. Each treatment was randomly

assigned to three l/60-acre plots that were laid out in

a completely randomized design. The study area was

located on an upland sandy loam in central Louisiana

in a stand of mixed hardwood brush composed

primarily of flowering dogwood (Cornus florida L.),

huckleberry (Gaylussacia spp.), red maple (Acer

rubrum L.), sweetgum (Liquidambar sfyraciflua L.),

and blackgum (Nyssa sylvatica Marsh.). Forty

hardwood stems per plot were randomly selected

and tagged from among the 21 species present.

Earlier unpublished research’ has shown topkills

of 97 percent to hardwood brush by 2,4,5-T ester

applied at 1 lb a*/A in late April followed by picloram at

4 lb a/Aa month later. Tebuthiuron applied at 4 lb a/A

on May 10 followed by triclopyr amine at 1.5 lb a/A on

June 24 caused topkills of 75 percent. This study

continued this work and tested several new combinations of herbicides for their effectiveness at low application rates.

The pellet herbicides were broadcast by hand on

April 12, 1977, and the liquid herbicides were applied

with a back pack mist blower on May 3, 1977. Water

was used as the carrier, with a spray volume of 20

gallons per acre.

Treatment effects were determined in late summer

by estimating percent topkill for each stem at the end

of the first and second growing seasons. Values for

the 40 plants sampled were then averaged to obtain a

METHODS AND MATERIALS

Previous work with hexazinone, picloram, and

tebuthiuron pellets indicates that they should give 80

3Hexazinone (3-cyclohexyl-6-(dimethylamino)-l-methyl-l,3,5-triazine-2,4 (1 H;SH)dione) as Velpar DPX-3674-1 OP.

Picloram (potassium salt of 4-amino-3,5,6-trichloropicolinic acid)

as Tordon 1 OK.

Tebuthiuron (1-(5-tert-butyl-l,3,4-thiadiazol-2-yl)-1-3-dimethylurea) as EL-103.

2,4,5-T ester (propylene glycol butyl ether ester of 2,4,5trichlorophenoxyacetic acid) as ESTERON 245.

Triclopyr ester (ethylene glycol butyl ether ester of 3,5,6-trichloro2-pyridyloxyacetic acid) as DOWCO 233 (M-4021).

‘McLemore, B. F. 1977. Unpublished data. U.S. Dep. Agric. For.

Serv., Southern Forest Experiment Station, Pineville, La.

2a - acid equivalent (2,4,5-T, triclopyr, picloram), active ingredient (hexazione, tebuthiuron).

Southern Forest Experiment Station/T-10210 U.S. Postal Services Bldg., 701 Loyola Avenue, New Orleans, La. 70113

Forest Service, U.S. Department of Agriculture.

Serving Alabama, Arkansas, Louisiana, Mississippi, Eastern Oklahoma, Tennessee, Eastern Texas.
percent topkill per plot. Percents were converted to

arcsin proportion for statistical analysis (ANOV .05).

Duncan’s Multiple Range Tests were used to

evaluate differences among treatment means.

RESULTS AND DISCUSSION

As mentioned earlier, average topkill of hardwood

brush should be 80 percent or better. The triclopyrpicloram combination was the only treatment to meet

this standard with a mean value statistically different

from unacceptable results (table 1). Also, the

triclopyr-picloram combination allowed no foliar recovery from the first to the second growing season.

Foliar recovery of the 2,4,5-T-picloram combination

was only 3 percent, which is acceptable. Visual

evaluation during inspection confirmed that the

triclopyr-picloram and the 2,4,5-T-picloram combinations both gave acceptable brush control through

two growing seasons. All other treatments were unacceptable.

Table 2 reports the control by species for the two

Table 2.-Topkill of hardwood species after two growing seasons

Table 1 .-Average topkill of hardwood brush after one and two

growing seasons

Treatment

Triclopyr ester + picloram

2,4,5-T ester + picloram

Triclopyr ester + tebuthiuron

Triclopyr ester + hexazinone

2,4,5-T ester + hexazinone

Triclopyr ester

2,4,5-T ester

2,4,5-T ester + tebuthiuron

Picloram

Tebuthiuron

Hexazinone

Topkill per

Rate of growing season

application 1st 2nd

Lb alA ____. percent-----

1.0 + 3.0 9 8 98la

1.0 + 3.0 9 2 89 ab

1.0 + 3.0 9 0 84 bc

1.0 + 3.0 8 5 75 bed

1.0 + 3.0 8 5 75 bed

1.0 8 0 70 cde

1.0 7 4 67 cde

1.0 + 3.0 7 9 67 ale

3.0 6 6 60 de

3.0 5 6 50 de

3.0 5 1 46 e

‘Percent topkills followed by the same letter are not significantly

different at the 0.05 level.

Hexazinone Tebuthiuron Picloram

Topkill

Triclopyr 2,4,5T 2,4,5-T Triclopyr

Species

Primary species:

Cornus florida L.

Gaylussacia spp.

Acer rubrum L.

Liquidambar styraciflua L.

Nyssa sylvatica Marsh.

Beech family:

Quercus stellata Wang.

Q. alba L .

Q. marilandica Muenchh.

Q . nigra L.

Q . falcata Marsh. var. falcata

Carya spp.

Fagus grandifolia Ehm

Minor species:

Prunus serotina Ehrh

Crataegus spp.

Viburnum dentatum L.

Hex opaca Ait.

Rhus copallina L .

Lo&era japonica Thumb.

Sassafras albidum (Nutt.) Nees

Callicarpa americana L.

Diospyros virginiana L .

PdlStS pellets pellets ester ester +picloram + pi&ram

________________________________________----------percent -_------- ________________________________________----------

73(16)’

2(36)

42(18)

84(23)

81( 7)

72(18) 83(25)

436) 58(20)

62(15) 41(35)

65(12) 86( 7)

47(14) lOO( 6)

70( 7)

49( 16)

63(29)

93(30)

lOO( 5)

76(17)

33(20)

54(33)

lOO(17)

lOO( 5)

lOO( 6)

80(24)

75(24)

96(30)

lOO( 9)

99(28)

95(27)

98(16)

lOO( 8)

lOO(12)

-

% ‘3)

lOO( 1)

lOO( 3)

lOO( 3)

-

lOO( 1)

lOO( 2)

20( 1)

-

-

-

-

lOO( 1)

12( 2)

15( 1)

lot 1)

55( 2)

lOO( 2)

-

62( 2)

53( 8)

w 4)

-

w 4)

lOO( 1)

lOO( 1)

15( 1)

w 4)

55( 3)

87( 5)

lOO( 1)

-

lOO( 1)

40( 1)

-

70( 2)

-

lOO( 2)

-

lOO( 1)

lOO( 5)

lOO( 1)

lOO( 6)

50( 2)

lOO( 2)

lOO( 1)

-

lOO( 3)

-

25( 1)

-

78( 8)

lOO( 3)

lOO( 4)

-

-

-

-

-

-

lOO( 2)

31(13)

72( 6)

-

lOO( 1)

-

-

-

-

62(10)

W 2)

lOO( 1)

-

79( 4)

lOO( 1)

82( 5)

-

-

lOO( 1)

-

-

40( 1)

-

-

lOO( 3)

35( 1)

-

lOO( 5)

lOO( 3)

lOO( 6)

lOO( 1)

-

lOO( 1)

lOO( 1)

-

- -

lOO( 1)

lOO( 3)

lOO( 1)

-

lOO( 5)

lOO( 3)

lOO( 1)

-

-

Average 47( 120)3 50(120) 60( 120) 71(120) 68( 120) 88(120) 98(120)

‘Number of stems treated.

2No data.

3Differences in percent between table 1 and 2 due to rounding error.

James D. Haywood is Assistant Silviculturist, Southern Forest Experiment Station, Forest Service-USDA, Pineville, Louisiana.

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acceptable treatment combinations and for each

single herbicide treatment. Hexazinone and

tebuthiuron are included because our rate is similar

to the full rate recommended by the manufacturers.

Hexazinone, picloram, triclopyr, and 2,4,5-T effectively controlled blackgum and sweetgum, and picloram also controlled flowering dogwood.

Tebuthiuron did poorly with all the primary species.

The 2,4,5-T-picloram combination successfully controlled all the primary species except red maple, while

the triclopyr-picloram combination was successful

with every species.

Not enough oak stems were treated to make valid

conclusions, but both tebuthiuron and the triclopyrpicloram combination were consistently effective in

controlling the few oaks present. The other treatments had varying results.

The two treatment combinations successfully controlled the minor mixed hardwoods, while results with

the single herbicide treatments were erratic.

In conclusion, each herbicide applied alone controlled certain species, but none gave the overall

brush control obtained with the two combinations.

This study confirmed positive results from earlier

studies with low dosages of 2,4,5-T, triclopyr, and

picloram. Site preparation using picloram pellets at 2

lb a/A followed by 2,4,5-T spray at 1 lb a/A should

cost $70 per acre. If triclopyr were used, the cost

would be higher; but it should be noted that triclopyr

ester is not labeled for herbicide use at present.

This publication reports research involving pesticides. It does not contain recommendations for their use nor does it imply that the uses discussed have been

registered. All uses of pesticides must be registered by appropriate State and

Federal agencies before they can be recommended.

Caution: Pesticides can be injurous to humans, domestic animals, desirable

plants, and fish or other wildlife -if they are not handled or applied properly. Use all

pesticides selectively and carefully. Follow recommended practices for the disposal of surplus pesticides and pesticide containers.

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* U.S. GOVERNMENT PRlNTlNG OFFICE: 1979%673.722/W247