@pia United States

Department of

Agriculture

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c45

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Forest Service

Southern Forest

Research Note

SO-372

Experlment Station May 1993

Stripping of Soil-Applied Hexazinone, Picloram, and Tebuthiuron for

Loblolly Pine Site Preparation

James D. Haywood

SUMMARY INTRODUCTION

Herbicides were applied to prepare two upland sites

for planting of loblolly pine (Pinus taeda L.) after clearcut

harvesting: (1) picloram pellets, (2) hexazinone liquid,

(3) a slurry of tebuthiuron soluble powder, and (4) following underplanting, a liquid formulation of picloram + 2,4-

D was injected into residual hardwoods. The herbicides

in treatments 1 through 3 were applied in 4-inch-wide

parallel strips spaced 98 feet apart in April 1981. On a

per-acre basis, the rates of application were 1.8 lb acid

equivalent picloram, 1.5 lb active ingredient (a.i.)

hexazinone, and 1.5 lb a.i. tebuthiuron. Vegetation on all

plots was prescribe burned in August 1981, and the plots

were planted in January 1982 with loblolly pine (Pinus

taeda L.) seedlings. Planting rows were evenly spaced

between the chemically treated strips. In treatment 4, all

hardwoods 1 inch or greater in diameter at breast height

(d.b.h.) were injected near groundline in April 1982.

Forest regeneration following clearcut harvesting is a

major concern in the Southern United States on both

private and public lands. On sites where pure pine

management is desirable, preparation before planting or

seeding often requires the piling, crushing, or killing of

residual trees and shrubs and possibly the destruction of

debris left from the harvesting operation. These practices can be expensive, and forest managers may seek

innovative site preparation methods that will reduce

costs but still result in the establishment of fast-growing,

well-stocked pine stands.

Although the competing plant cover varied somewhat

among the four site preparation treatments, one growing

season after the pines were planted, loblolly pine survival, height, and diameter growth were not affected by

treatment at either site through five growing seasons.

Evidently, stripping soil-active herbicides as a means of

preparing loblolly pine planting sites is no better than

single-tree injection of the larger hardwoods left after

clearcut harvesting.

Herbicides are an alternative to mechanical methods

for preparing pine sites for regeneration. They are normally broadcast either as foliar sprays or in pellet formulations. Under certain conditions, injection of individual stems with a herbicide may be the best means

of chemically treating the residual vegetation. Chemically treated sites are usually prescribe burned before

planting or seeding.

Keywords: Chemical site preparation, Pinus taeda L.,

single-tree injection, soil-active herbicides, underplanting

The application of soil-active herbicides in narrow

parallel strips is another way to control vegetation. Concentrating the herbicide in a limited volume of soil should

control plants with roots growing within these narrow

strips of soil. Pine seedlings that were planted or

developed from seeds between these strips would not

be injured. Conceptually, once the pine root systems

grow into these treated strips of soil, the residual concentration of herbicide would be insufficient to harm the

regeneration because, over time, herbicides are biologiSouthern Forest Experiment Station/T-102lO U.S. Postal Services Bldg., 701 ‘Loyola Avenue, New Orleans, La. 70113

Forest Service, U.S. Department of Agriculture.

Serving Alabama, Arkansas, Louisiana, Mississippi, E. Oklahoma, Tennessee, E. Texas, Puerto Rico, U.S. Virgin Islands

1
tally degraded, absorbed by plants, or leached from the

root zone. The application of herbicides to narrow parallel strips can be done by hand using granular formulations or by dispensing a liquid concentrate or slurry with

backpack equipment. The tract can be any size or

shape. Drift is not a concern because dry materials or

coarse sprays are used.

To test the concept of using stripping as a means of

herbicide site preparation, two clearcut-harvested sites

were treated with three soil-active herbicides for comparison to single-tree injection. The objectives were to

determine (1) whether strip application was a reasonable

method of site preparation for regenerating loblolly pine

(Pinus taeda L.), (2) whether one herbicide treatment

was better than the others, and (3) what the initial effects

were of herbicide use on the existing plant community.

STUDY AREAS

Two study areas were selected in central Louisiana

that had been clearcut harvested. Site 1 is a Gore very

fine sandy loam (Vertic Paleudalfs, fine, mixed, thermic)

with a 1- to 5-percent slope. It is moderately well drained

with a clayey subsoil and has low natural fertility,

medium runoff, and slow water movement through the

soil (Kerr and others 1980). Severe drought stress can

develop during summer, but this soil can become waterlogged for extended periods during winter. It is a

moderately productive soil with a site index (base age 50

years) of 75 feet for loblolly pine.

Site 2 is a complex of soils, but the major soils are

Beauregard silt loam (Plinthaquic Paleudults, fine-silty,

siliceous, thermic) and Ruston fine sandy loam (Typic

Paleudults, fine-loamy, siliceous, thermic) with a 1- to 3-

percent slope. The Beauregard silt loam is moderately

well drained; it has low natural fertility, slow runoff, and

slow water movement through the soil (Kerr and others

1980). Severe drought stress can develop during summer, but this soil can become waterlogged for extended

periods during winter. It is a highly productive soil with a

site index (base age 50 years) of 90 feet for loblolly pine.

The Ruston sandy loam is well drained; it has low

natural fertility, medium runoff, and moderate water

movement through the soil. Roots penetrate easily. A

seasonally high water table is below 6 feet. It is a highly

productive soil with a site index (base age 50 years) of

90 feet for loblolly pine.

After clearcut harvesting, both sites were left fallow for

at least a year. At Site 1, the common residual plants

were sweetgum, Liquidambar styraciflua L.; blackgum,

Nyssa sylvatica Marsh.; post oak, Quercus stellata Wangenh.; red maple, Acer rubrum L.; flowering dogwood,

Cornus florida L.; American beautyberry, Callicarpa

americana L.; southern bayberry, Myrica cerifera L.;

shining sumac, Rhus copallina L.; yaupon, llex vomitoria

Ait.; and several hawthorns, Crataegus spp.; blackberries, Rubus spp.; and blueberries, Vaccinium spp. At

Site 2, the common residual plants were post oak; black

cherry, Prunus serotina Ehrh.; sweetgum; red maple;

blackjack oak, Q. marilandica Muenchh.; southern red

oak, Q. falcata Michx. var. falcata; American holly, 1 .

opaca Ait.; mockernut hickory, Carya tomentosa (Poir.)

Nutt.; flowering dogwood; shining sumac; southern

bayberry; and several hawthorns, blackberries, and

blueberries.

METHODS

Experimental Design and Treatment

At each site, four blocks of four site preparation treatments each were established in a randomized complete

block design; the blocks served as replicates. Blocking

was based on the species richness and abundance of

brush species (small trees and shrubs less than 1 inch in

diameter at breast height [d.b.h.]) at 4.5 feet above

groundline and on slope.

Each of the 32 plots (2 sites by 4 blocks by 4 treatments) measured 117.6 by 72.6 feet (0.196 acre). Because concentrated strips of herbicides would be applied, the plots were wider than normal for the planting

scheme to provide sufficient buffer between the outside

herbicide strip and the plot edge. Also, plots were

separated from each other by 16.4-foot buffers.

An inch and a half of rain fell on March 27 and 28,

1981, so the soil was well watered several days before

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

Experiment Station, Pineville, LA 71361-5500.

The products used for soil application were Velpar@ L (hexazinone [3-cyclohexyl-6-(dimethylamino)-1 -methyl-l ,3,5-triazine-2,4(1 H,BH)-dione]), Tordon@ 1 OK (picloram [4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid]), and Spike@ 6OW (tebuthiuron [N-[5-(1 ,l-dimethylethyl)-1,3,4-thiadiazol-2-

yl]-N,N’-dimethylurea]). Tordon@ 101 Mixture (picloram + 2,4-D [2,4-dichlorophenoxylacetic acid]) was used for tree injection. Use of trade names is

solely for the benefit of the reader, and discussion of herbicides in this paper does not constitute recommendation of their use or imply that the uses

discussed here are registered. If herbicides are handled, applied, or disposed of improperly, there is potential for hazards to the applicators, off-site

plants, and the environment. Herbicides should be used only when needed and should be handled safely. Follow directions and heed all precautions

on the container label.

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

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the soil-active herbicides were applied at both sites. On

April 1 and 2, 1981, the herbicides were singly applied in

parallel strips to treatments 1 through 3. The three herbicide formulations used were either picloram pellets,

hexazinone liquid, or a slurry of tebuthiuron wettable

powder. The herbicide was concentrated in strips 4 inches wide and 72.6 feet long spaced 9.8 feet apart.

Within these strips, rates of application were 54 lb acid

equivalent (a.e.) picloram, 46 lb active ingredient (a.i.)

hexazinone, or 46 lb a.i. tebuthiuron per acre. On a peracre basis, the application rates were 1.8 lb a.e.

picloram, 1.5 lb a.i. hexazinone, or 1.5 lb a.i. tebuthiuron

per acre.

All plots were prescribe burned in August 1981. At Site

1, most of the large hardwoods (1 inch or greater in

d.b.h.) were killed back to groundline. Only half of the

large hardwoods at Site 2 were killed back.

All plots were planted in January 1982 with 1-O bareroot loblolly pine seedlings. Each plot contained 11 rows

of 11 planted pines each. The rows were spaced 9.8 feet

apart, and the trees were spaced 6.6 feet apart within

rows. The planting rows were evenly spaced between

the chemically treated strips, so none of the seedlings

were planted in the strips.

For comparison purposes, an underplant-inject treatment was installed in April 1982 as the fourth site

preparation treatment. On these plots, all hardwoods 1

inch or greater in d.b.h. were injected near groundline

with a picloram + 2,4-D formulation.

Measurements and Data Analysis

The center 49 planted loblolly pines comprised each

measurement plot (0.073 acre). Within each measurement plot, four 9.8- by 6.6-foot subplots were systematically located. These subplots were used to collect data

on brush, vine, and herbaceous vegetation. Brush

species were identified, rootstocks counted, and heights

measured one growing season after the pines were

planted. The identity and coverage of vines and herbaceous plants was determined. Coverage was defined

as the percent of area the herbaceous plants and vines

would shade if the sun were directly overhead.

Within each 0.073-acre measurement plot, large

hardwoods (1 inch or greater in d. b. h.) were identified,

and total height and d.b.h. measured one growing

season after the pines were planted. Planted loblolly

pines were counted and heights measured through five

growing seasons. Pine d.b.h. was measured after five

growing seasons.

For each site, percentage of herbaceous plant and

vine cover; number of rootstocks per acre; height of

brush; and percentage of survival, height, and d.b.h. of

planted loblolly pines were analyzed by analyses of

variance (Probability >F-value = 0.05). Duncan’s Multiple Range tests were used to determine means separation if necessary.

Statistical analysis of the large hardwood data was not

practical because the large hardwoods were scattered at

both sites and because plot layout did not provide for a

representative sample on each plot. General comments

about the species richness and abundance of large

hardwoods were made, however.

RESULTS AND DISCUSSION

Competing Vegetation

One growing season after the pines were planted, herbaceous vegetation covered 63 and 69 percent of the

plot surface at Sites 1 and 2, respectively (table 1).

There were no significant differences among site

preparation treatments at either site.

Table 1 .-Percentages of herbaceous plant and vine cover and the number and height of competing

trees and shrubs less than 1 inch in d.b.h. one growing season after the pines were planted*

Herbaceous Vine Rootstocks/acre Tree and

Site and treatment cover cover Tree Shrubs shrub height

__________ Percent __________ __________ Count __________ Feet

Site 1

Underplant-inject 59a la 1,175a 6,325a 1.8a

Picloram 56a la 1,175a 4,050a l.lb

Hexazinone 71a la 1,075a 5,lOOa 1.9a

Tebuthiuron 65a 2 a 975a 3,500a 1.2b

Average 6 3 1 1,100 4,744 1.5

Site 2

Underplant-inject 62a 3 a 3,125a 6,400a 1.7a

Picloram 71a la 1,175a 4,350a 0.9b

Hexazinone 67a la 3,075a 6,325a 1.5a

Tebuthiuron 77a la 2,350a 6,200~ 1.4a

Average 6 9 1 2,431 5,819 1.4

*For each site, columnar means followed by the same letter are not significantly different based on

Duncan’s Multiple Range Tests (ProbabilitysF-value=O.O5). 3
Table 2.-Number, d.b.h., and height of hardwoods 1 inch or greater in d.b.h. one

growing season after the pines were planted at Site 1

Treatment

Variable and Underplantspecies inject Picloram Hexazinone Tebuthiuron

_______________________________ Stems/acre _________________________________

Number

Post oak 3 6 5 3 0

Mockernut hickory 0 3 0 0

Sweetgum 0 1 4 3 7

Tree sparkleberry 0 0 3 0

Southern red oak 0 0 0 3

Total/acre 3 8 2 9 1 0

_________________________________ Inches ______________________________________

D.b.h.

Post oak 6.5 5.1 3.3 0.0

Mockernut hickory . O 2.7 . O . O

Sweetgum .O 2.5 1.7 6.5

Tree sparkleberry . O . O 3.1 . O

Southern red oak . O . O .O 6.8

Weighted mean 6.5 4.6 2.7 6.6

Height

Post oak

Mockernut hickory

Sweetgum

Tree sparkleberry

Southern red oak

Weighted mean

___________-_-__--__------------- /z&q __________-_________---------------------

43.0 31.5 21.7 .O

. O 19.4 . O . O

. O 19.7 12.5 17.7

. O . O 10.8 . O

.O .O .O 38.1

43.0 29.0 15.0 23.8

At Site 1, typical herbaceous plants were panicums,

Pan&m spp. and Dichanthelium spp.; bluestems,

Andropogon spp. and Schizachyrium spp. ; common carpetgrass, Axonopus affinis Chase; paspalums,

Paspalum spp.; hairy crabgrass, Digitaria sanguinalis

(L.) Stop; three-awns, Aristida spp.; pinehill beak-rush,

Rhynchospora globularis (Chapm.) Small; sunflowers,

Helianthus spp.; asters, Aster spp.; eupatoriums,

Eupatorium spp.; fireweed, Erechitites hieracifolia (L.)

Raf.; daisy fleabane, Erigeron strigosus Muhl. ex Willd.

var. beyrichii(Fisch. & Mey.) T.&G. ex Gray; goldenrods,

Solidago spp.; mountainmints, Pycnanthemum spp.;

mecardonia, Mecardonia accuminata (Walt.) Small; and

hypericums, Hypericum spp. At Site 2, typical herbaceous plants were panicums; bluestems; common

carpetgrass; paspalums; uniola grasses, Chasmanthium

spp.; pinehill beak-rush: sunflowers; eupatoriums;

fireweed; daisy fleabane; mountainmints; mecardonia;

Maryland meadowbeauty, Rhexia mariana L.; and

southern bracken, Pteridium aquilinum (L.) Kuhn var.

pseudocaudatum (Clute) Heller.

Vines covered 1 percent of the plot surface at both

study sites, and there were no significant differences

among treatments (table 1). At both sites, typical species

were Carolina jessamine, Gelsemium sempervirens (L.)

Ait. f.; poison ivy, Toxicodendron radicans (L.) Kuntze; .

muscadine grape, Vitis rotundifolia Michx.; greenbrier,

Smilax spp.; Virginia creeper, Parthenocissus quinquefolia (L.) Planch; and Alabama supplejack, Berchemia scandens (Hill) K. Koch. Cross-vine, Bignonia

capfeolata L., was also typical at Site 1.

The number of small hardwood tree rootstocks

averaged 1 ,100 and 2,431 per acre at Sites 1 and 2,

respectively, and shrub rootstocks averaged 4,744 and

5,819 per acre at Sites 1 and 2, respectively (table 1).

There were no significant treatment effects on the number of small trees and shrubs per acre at either site.

At both sites, typical brush species were sweetgum,

American beautyberry, shining sumac, southern bayberry, and several blackberries. Southern red oak; black

cherry; St. -Andrews-Cross, Hypericum hypericoides (L.)

Crantz; and several blueberries were also typical at

Site 2.

At Site 1, average height of brush was significantly

less on the picloram and tebuthiuron treatments than on

the underplant-inject and hexazinone treatments (table

1). At Site 2, the brush was shorter on the picloram treatment than on the other three treatments.

At Site 1, the picloram treatment left more large

hardwoods per acre than the other treatments (table 2).

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Table 3.-Number, d.b.h., and height of hardwoods 1 inch or greater in d.6.h. one

growing season after the pines were planted at Site 2

Treatment

Variable and

species

Underpiantinject Picloram Hexazinone Tebuthiuron

Number

Sweetgum

Blackgum

Mockernut hickory

Southern red oak

Black cherry

Post oak

1 1 0 0 3

1 0 3 7 3

7 3 1 0 0

0 1 7 3 3

0 0 3 0

0 0 1 4 0

Total/acre 2 8 2 3 3 7 9

D.b.h.

Sweetgum

Blackgum

Mockernut hickory

Southern red oak

Black cherry

Post oak

Weighted mean

Height

Sweetgum

Blackgum

Mockernut hickory

Southern red oak

Black cherry

Post oak

42.7 .O . O 28.9

24.6 5.9 23.3 5.3

26.5 45.0 19.0 .O

. O 45.3 29.9 56.1

. O . O 46.9 . O

. O . O 45.0 . O

Weighted mean 32.2 40.1 32.8 30.1

______________-----------------Stems/acre_______-----________--------------

_________________________________ l,,&,es__-___________________________________

8.0 0.0 0.0 4.8

4.1 2.5 4.6 1.4

4.2 9.7 5.7 . O

.O 11.0 3.7 11.2

. O . O 5.9 .O

.O . O 8.2 .O

5.7 9.7 6.3 5.8

_________________________________ &et_-_----_________---_____________________-

However, as stated previously, valid statistical comparisons could not be made. At Site 2, the number of

large hardwoods per acre was similar among treatments

(table 3).

Loblolly Pine

After planting, a winter/spring drought occurred at both

sites. At Site 1, the January 1982 rainfall deficit was 2.6

inches below a 31 -year average for the location, and by

July, the rainfall deficit was 9.7 inches below this

average. At Site 2, the January 1982 rainfall deficit was

1.8 inches below a 39-year average for the location, and

by July, the rainfall deficit was 5.9 inches below this

average. Rainfall remained well below normal for the

year at both sites until above-normal rainfall occurred in

November and December. The drought probably had a

negative effect on the newly planted seedlings because

survival averaged 55 and 73 percent at Sites 1 and 2,

respectively, with no significant treatment effects on pine

survival one growing season after the pines were

planted (table 4).

Table 4.-Lob/o//y pine survival one and five growing seasons after

pines were planted and pine height and d. b. h. after 5 years l

Survival 5th year

Site and treatment 1 st year 5th year Height D.b.h: ”

_- ____percent __________ feet Inches

Site 1

Underplant-inject 50a 47a 12.4a 1.9a

Picloram 58a 54a 11.4a 1.6a

Hexazinone 54a 52a 10.9a 1.6a

Tebuthiuron 60a 55a 11.8a 1.8a

Average 5 5 5 2 11.6 1.7

Site 2

Underplant-inject 70a 60a 11.2a 1.4a

Picloram 77a 71a 10.7a 1.3a

Hexazinone 79a 69a 11.6a 1.4a

Tebuthiuron 68a 62a 11.6a 1.5a

Average 7 3 6 5 11.3 1.4

‘For each site, columnar means followed by the same letter are not

significantly different based on Duncan’s Multiple Range Tests (Probability>F-value=O.05).

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Loblolly pine survival remained relatively stable after

the first year, and survival after five growing seasons

averaged 52 percent at Site 1 and 65 percent at Site 2

(table 4). Five-year-old loblolly pine height averaged

11.6 and 11.3 feet, and d.b.h. averaged 1.7 and 1.4 inches at Sites 1 and 2, respectively. There were no sig-

’ nificant treatment effects on 5-year survival, height, or

d.b.h. at either site.

Hardwood competition seemed sufficient at both sites

to influence seedling loblolly pine development

(Haywood and Toliver 1989, Tiarks and Haywood 1986).

However, pine height growth was comparable to other 5-

year-old planted loblolly pine stands growing on

moderately to highly productive silt loam soils in central

Louisiana where established grasses rather than

hardwoods were the primary competitors (Haywood and

Toliver 1989). In Haywood and Toliver’s (1989) study,

delays in establishment of pine regeneration led to a

reduction in sapling pine growth within mixed pinehardwood stands. This result was apparently avoided in

the present study because the established pine

regeneration had been planted in a timely manner-10

months after the soil-active herbicides were stripped and

5 months after the prescribed burn.

CONCLUSIONS

One growing season after loblolly pines were planted,

both sites supported high populations of herbaceous,

vine, and woody competitors regardless of site preparation treatment. Although there were some differences in

competing plant populations among treatments, loblolly

pine survival, height, and diameter growth were not affected by site preparation method through five growing

seasons at either site. Evidently, stripping soil-active

herbicides as a means of preparing pine planting sites is

no better than single-tree injection of the larger residual

hardwoods left after clearcut harvesting. However, all

four treatments were successful in establishing pine

regeneration. The most detrimental factor was the

drought during the first growing season, which most likely resulted in the relatively poor seedling survival on all

treatments.

LITERATURE CITED

Haywood, James D.; Toliver, John R. 1989. A comparison of loblolly pine growth and yield on pure pine

and mixed pine-hardwood sites. In: Waldrop, Thomas

A., ed. Proceedings pine-hardwood mixtures: a symposium on management and ecology of the type; 1989

April 18-19; Atlanta, GA. Gen. Tech. Rep. SE-58.

Asheville, NC: U.S. Department of Agriculture, Forest

Service, Southeastern Forest Experiment Station:

117-l 22.

Kerr, A., Jr.; Griffis, B.J.; Powell, J.W. [and others]. 1980.

Soil survey of Rapides Parish, Louisiana. Alexandria,

LA: U.S. Department of Agriculture, Soil Conservation

Service and Forest Service in cooperation with:

Louisiana Agriculture Experiment Station. 86 p.

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.

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