@ United States 

Department of 

Agriculture 

Forest Service 

Southern Forest 

Experiment Station 

New Orleans, 

Louisiana 

Research Paper 

SO-277 

September 1993 

Effects of Aeria 

yphosate and Hexazinone on 

oods and Pines in a 

y Pine P antation 
Areas in a 4-year-old loblolly pine (Pinus taeda L.) plantation 

were treated with aerially applied Roundups (glyphosate), Pronones 106 (hexazinone), and Velpar@ L (hexazinone) plus Lo Drifts 

(a spray additive). All herbicides were applid with appropriate 

helicopter-mounted equipment. The proportion of free-to-grow pine 

trees increased over a 2-year period in both the treated and untreated areas, but the increase was slightly geater in the treated 

areas. Final loblolly pine height, d.b.h., and volume per tree did not 

differ significantly among the four treatments. About 1,200 hardwood trees and 4,700 shrubs over 3 ft tall per acre were present at 

the beginning of the study. 

The author wishes to recognize Thomas E. (ficker) Campkll for 

initiating this research and for his years of service in the advancement of forest science; International Paper Company, which provided the study area and the helicopter used to apply treatments; 

and Monsanto Company (Roundup@), DuPont Agrichemicals 

(Velpars L), and Pro-Serve, Inc. (Pronone@ 1061, which supplied 

herbicides, guidance, and assistance in installing the treatments. 
Effects of Aerially Applied Glyphosate 

Hexminone on Hardwoods Pines in a 

Loblolly Pine P1 

Many species of hardwood trees and shrubs sprout 

prolifically after clearcut harvesting and site preparation on forest lands where managers are attempting to 

establish loblolly pine (Pinus taeda L.) planttPlions. 

Native early successional species also reappear and 

compete vvith plant& pines on such sites (Swindel and 

others 1983). To establish and maintain dominant 

stands of pines and to increase pine productivity, it 

may be necessary to rellease pines from competing trees 

and shrubs (Clason 1984, Glover and Dickens 1985, 

Hawood 1986). 

Herbicides are often used to free or release pine trees 

from competition vvith trees and shrubs that overtop or 

closely surround them (Ford-Robertson 1971). This 

study tested the effectiveness of three herbicides 

IakIed for broadcast aerial application to release loblolIy pines from competition. The herbicides tested 

were Roundup@, glyphosate (N-[phosphonomethylIglycine); Pronones 106, hexazinone ~3-cyclohexyl-6- 

Idimethylaminol- 1-methyl- 1,3,5-triazine-2,4[1 W,3H]- 

dione); and Velpara L, hexazinone. The objectives were 

to evaluate and compare the follo+ng: (1) brush control efficaey of these products (reduction in number of 

hardwood stems per acre and shade competition), (2) 

the tolerance of loblolly pine to these products (injury 

and survival), and (3) the height, d.b.h., and volume 

response of pine saplings to release treatments. 

The study area is on rolling terrain in central Louisiana. The sandy loam topsoil is 10 to 14 inches in 

thickness. The subsoil is a sandy clay loam and silt lorn. 

In early 1981, the site was machine planted with 

irnpmved bare-root Ioblolly pine seedlinm on a spaeing of 

appro~mately 7 by 10 ft. In January 1982, there were 

526 living IobloHy pine seedlings per acre on the site. 

Four growing seasons after planting, it appeared 

that both hardwood and herbaceous vegetation were 

affeteling pine development. Hardwoods more than 3 ft 

tall number& about 5,900 per acre. Of these hardwoods, about 900 per acre were of species considered 

serious long-term competitors of planted pines (Haywood 1985). Another 300 hardwood trees per acre were 

probably developing too slowly to be a serious threat to 

establish& pine saplings. The other 4,700 stems per 

acre were shrubs. 

Competing hardwoods included shining sumac 

(Rhus copallina L.) (42 percent of stems), American 

beautyberry (Calliearpa americana L.) (15 percent of 

stems), sweetgum (Liquidambar styraciflua L.) (9 percent of stems), southern bayhrry (Myrica cerifera L.) 

(8 percent of stems), tree sparkleberry (Vaccinium 

arboreum Marsh.) (5 percent of stems), blackgum 

(Nyssa sylvatiea Marsh.) (4 percent of stems), red 

maple (her rubrum L.) (3 percent of stems), eastern 

baccharis (Baccharis halinifolta L.) (3 percent of 

stems), water oak (Quercus nigra L.) (2 percent of 

stems), and common persimmon (Diospyms virginiana 

L.) (2 percent of stems). The remaining 7 percent of 

hardwood stems were southern red oak (Q. falccnta var. 

falcata Michx.), post oak (Q. stellata Wangenh.), blackjack oak (Q. marilandica Muenchh.), white oak (&. 

alba %.I, bluejack oak (Q. incana Bartr.), willow oak (Q. 

pkellos L.), live oak (&. uirginiana Mill.), chinkapin oak 

(&. muehlenbergii Engelm.), hickory (Carya spp.), 

Rowering doguvood (Cornus florida L.), black cherry 

(Prunus serotina Ehrh.), green ash (Fraxinus pennsylvaniea Marsh.), winged elm (Ulrnus alata Michx.), 

sassafras (Sassafras albidum (Nutt.) Nees), American 

holly (]la opaca Ait.), sweetleaf (Symplocos tiizctoria 

[L.] L'Her.), witch-hazel (Hamamelis uirginiana L.), 

hadhorn (Crataegus spp.), devils-walkingstick (Aralia 

spinosa L.), yaupon (Ila vomitoria Ait.), arrowwood 

(Viburnum dentatum L.), fringetree (Chionanthus virgznicus L.), and plum (Prunus spp.). 

James DD. Haywood is a silvidturist at the Alexandria Forestry Center, U.S. Department of Agriculture, Forest Service, Southern Forest Experiment 

Station, Pineville, LA 71361-5500. 

1 
METHODS 

Experimental Besi- md Treatments 

Effects of three pine-release herbicide treatments 

were compared to effects in an untreated check in a 

randomized complete block design experiment. Three 

blocks were established based on vegetation and slope 

within different areas of the stand. There were 12 plots 

(4 treatments by 3 blocks). The treatments were randomly assigned within the blocks. 

The plots were established in the field during July 

and August 1984. Each plot was 850 ft long. The untreated check plots were 150 ft wide. Roundup and 

Velpar L plots were 200 ft wide (four 50-ft-vvide spray 

swaths). The Pronone 10G plots were 240 ft wide (three 

80-ft-wide spray swaths). The different plot widths 

were nwessary bwause the helicopter-mounted equipment used to apply individual herbicides produced different swath widths. 

Three subplots for pine measurement were established along the centerline of each plot. Each subplot 

was 46.7 ft2 (0.05 acre). Subplots were not located in 

drainages and openings. The centers of the subplots 

were at least 124 ft from the plot ends. They were at 

least 124 ft apart and at least 50 ft from the plot edge. 

Four hardwood assessment sub-subplots with radii 

of 6.5 ft (0.003 acre) were established within each pine 

measurement subplot. The sub-subplots were located 

just inside each of the corners of the pine measurement 

subplots. 

The treatments were: (1) untreated check: no herbicide treatment; (2) bundup: two qt of Iiquid product 

(1.5 Ib acid equivalent) in 9.5 gal water per acre; (3) 

Pronone 106: 20 lb of granular product (2 lb active 

ingredient Ta.i.1) per acre; and (4) Velpar L: four qt of 

liquid product (2 Ib a.i.) plus 1.2 oz of Lo Drift@ (a spray 

additive) in 9 gal of water per acre. 

The bundup was applied between 10 and 10:30 a.m. 

on Septembr 13, 1984, at the end of the fourth growing season, with a helicopter-mounted Microfoil@ boom 

with triple-row 0.016 nozzles. The sky was bright and 

clear, and the ambient temperature was from 80 to 

85 OF. Winds were generally calm. 

The Pronone 106 was applied between 10 and 10:30 

a.m. on May 7, 1985, at the beginning of the fifth 

growing season, with a bucket-tme distributor slung 

beneath a helicopter. The sky was fair and hazy, and 

the ambient temperature was 76 OF1 Winds were 2 to 3 

rnik. 

The Velpar L was applied between 6330 and 7:15 a.m. 

on June 24,1985, at the beginning of the fifth growing 

season, with a helicopter-mounted Simplex@ 4900, 

series spray system fitted with T-Jet@ Straight 

Through nozzles with D-12 orifices. The sky was sunny 

and slightly hazy with an ambient temperature of 

73 OF. Winds were calm. 

More than 2.5 inches of rain fell on the study site 

within 2 weeks of the Pronone 106 application. About 2 

inches of rain Eel1 on the site during the mnth before 

application of Velpar L. In both instances, rainfall 

should have been sufficient to aid in dispersal of the 

herbicide through the soil. 

Measurements and Data hdysis 

Before treatments were applied, all pines in the subplots were identified with numbered metal tags. Their 

total height was measured to the nearest 0.1 ft, and 

their d.b.h. was measured to the nearest 0.1 inch. For 

each pine, shade competition was classified before 

treatment and two growing seasons after treatment. 

Classifications were as follows: 

0: Free-to-grow - competing vegetation shades the 

pine's crown on less than 30 percent of the 

crown's circumference. 

1: Mild competition - competing vegetation prevents up to 10 percent of overhead light from 

reaching the pine's foliage on 30 to 70 percent of 

the crown's circumference. 

2: Serious competition -competing vegetation prevents 11 to 60 percent of overhead light from 

reaching the pine's foliage on 71 to 100 percent of 

the crown's circumference. 

3: Suppressed-less than 11 percent of overhead 

light is reaching the pine, and the pine is almost 

completely overtopped. 

Sublethal herbicidal injury to pines was assessed 

annually for two growing seasons after treatments 

were applied. Injury was classified as follows: 

0: No visible injury. 

1: 50 percent or less of the crown shows needle 

discoloration, malformation, and tip burn on the 

lateral branches. 

2: More than 50 percent of the crown shows needle 

discoloration, malformation, and tip burn on the 

lateral branches, and 50 percent or less of the 

branch leaders have been killed. 

3: More than 50 percent of the crown shows needle 

burn or defoliation, and more than 50 percent of 

the branch leaders have been killed. 

4: Crown is severely damaged; tree not expected to 

survive. 

Pine height and d.b.h. were remeasured mnually for 

3 years after treatment. The final measurements were 

made in April 1988, while the pines were in their 

eighth grouring season after planting. Total inside-bark 

stern volumes were calculated with Schmitt and 

Bower's (1970) formula. 

In each sub-subplot, all hardmod sterns more than 3 

ft tall were identified by spsies and count& before and 

for two grovving seasons after treatment. 

Initial hardwood stochng, initial shade competition, 

pine survjivali, and initial pine height and d.b.h. data 
were analyzed with analyses of variance. Were treatment diflerences were found, Duncan's Multiple Range 

Tests were used to determine mean separations (Probability > F-value = 0.05). Wuctions in hardwood stocking, changes in shade competition, and pine d.b.h., 

height, and volume data were analyzed with analyses of 

covariance. The covariate in each analysis was the 

appropriate pretreatment data (Probability > F-value 

= 0.05). Data on sublethal pine damage caused by 

herbicide use are present& without analysis. 

RESULTS 

One growing season after application of pine release 

treatments, number of hardwoods in the Roundup and 

Pronone 106 plots decreased by 3,354 and 2,653 stems 

per acre, respectively (table 1). Hardwood stocking in 

the Velpar L plots did not decrease initially, but 

dwreasd by 858 stems per acre by the end of the 

second growing season. Two growing seasons after 

treatments were applid, the Roundup and Pronone 

106 plots had 3,191 and 2,580 fewer hardwood sterns 

per acre, respwtively. Sub-subplot data on hardwood 

stocking were highly variable, and thus there were no 

statistically significant differences in the reduction of 

hardwood stems per acre Lm wowing seasons after 

herbicide treatment (Probability > F-value = 0.0783). 

Loblolly Pines 

Before treatments were applid, an average of 67 

percent of the 4-year-old planted loblolly pine trees 

were considered fpee-to-grow, and the proportion of 

free-to-grow pine saplings did not diEer signifieantly 

among treatments (table 2). The pretreatment proportion of suppress& trees ranged from 1 to 4 percent. 

Tvvo years after treatments were applied, the average 

proportion of free-to-grow pine trees had increasedl 

from 67 percernG to 92 percent, and there were still no 

significant by-treatment differences in the proportion 

of free-to-grow pine saplings (table 2). The proportion 

Table 1. -Per-acre number of hardwood stems more than 3 ft tall before, and for two growing seasons 

after, pine-release treatment* 

Herbicide First Second 2-year 

treatment Initial growing season growing season change 

-----------%-------------------------- Stems/mre ...................................... 

Roundups 6,682a 3,32813 3,490a 3,191a 

Pronone@ 106 5,406a 2,753b 2,826a 2,580a 

Velpar" L 5,588a 5,643a 4,730a 858a ............................. PdabilLties > F-valuet .............................. 

Treatment effects 0.3357 0.0358 0.0783 0.0783 

*Columnar values followed by the same letter are not significantly different based on Duncan's 

Multiple Range Ssts (Probability > F-value = 0.05). 

*Probabilities are based on analysis of covariance with initial number of stems per acre as the 

covariate 

%ble 2. -Proportion of loblolly pines assigned to each of four shade classifications before and two 

growing seasons aper pine-release treatment 

Initial shade classification* 2nd-year shade classification* 

Treatments 0 1 2 3 0 1 2 3 

............................................ Pfercent ------ ....................................... 

Roundup@ 71 21 7 I 92 7 1 0 

Pronone@ 106 6 1 28 7 4 95 2 1 2 

VeIpar@ L 64 24 10 2 93 4 2 1 

Untreated check 72 22 4 2 89 8 2 I 

................................. Pdabilities > F-valuet .................................. 

Treatmenteffects 0.5066 0.4913 0.4577 0.6462 0.0789 0.1868 0.6506 0.8578 

*Shade classifications: 0: Free-to-pow - competing vegetation shades the pine's crown on less than 

30 percent of the crown's circumference, 1: Mild competition- hardwood vegetation prwents up to 10 

percent of overhead light from reaching the pine's foliage on 30 to 70 percent of the crown's 

circumference, 2: Serious competition - hardwood vegehtion prevents 11 to 60 percent of overhead 

light from reaching the pine's foliage on 71 to 100 percent of the crown's circumfeerence, and 3: 

Suppressed-less than 11 percent of overhead light is reaching the pine, and the pine is almost 

completely overtopped. 

+None of the columnar values were significantly different based on analyses of variance or 

covariance (Probability > F'-value = 0.05). 
Table 3. -Proportion of loblolly pine trees assigned to each of four sublethal damage 

categories for two growing seasons after pine-release treatment 

1-year damage category* 2-year damage category* 

Treatments 1 2 3 4 1 2 3 4 

................................... Percent -------------- ..................... 

Roundup" 8 1 2 0 6 0 0 0 

Pronone@ 10G 4 2 1 3 2 0 0 0 

Velpar@ L 1 1 0 0 0 0 0 0 

"Damage categories: 1- 50 percent or less of the crown shows needle discoloration, 

malformation, and tip burn on the lateral branches; 2 -More than 50 percent of the 

crown shows needle discoloration, malformation, and tip burn on the lateral 

branches, and 50 percent or less of the branch leaders have been killed; 3-More 

than 50 percent of the crown shows needh burn or defoliation, and more than 50 

percent of the branch leaders have been killed; and 4 -Crown is severely damaged; 

Table 4.-Average initial height and d.b.h. of loblolly pines four growing seasons after planting 

(measured in September 19841; and survival, height, d.b.h., and inside-bark uolume per 

loblolly pine in their eighth gmwing season after planting (measured in April 1988) 

Initial data? Final datat 

Treatments* Height D.b.h. Survival Height D.b.h. Volume 

Feet Inches Percent Ft Inches Ft31tree 

Roundup@ 7.7 0.9 96 16.2 2.9 0.44 

Pronone@ 10G 8.7 1.1 7 1 18.5 3.3 0.57 

Velpar@ L 7.6 0.9 96 17.9 3.1 0.50 

Untreated check 7.1 0.8 99 17.4 3.0 0.44 .................................. P&abilitks > F-ualue .................................. 

Treatment effects 0.1178 0.1086 0.1377 0.2230* 0.7014' 0.7814' 

*The pine-release treatments were applied at different times because these products work best 

when used in specific seasons of the year and kuse of operational constraints. The Roundup 

treatment was installed in September 1984. The Pronone 106 and Velpar L treatments were instdIed 

in May and June 1985, respectively. 

?None of the columnar means were significantly different based on analysis of variance or 

covariance (Probability > F-value = 0.05). 

'Probabilities are based on analysis of covariance with initial height as the covariate. If initial 

d.b.h. is used as the covariate, the probabilities are 0.1373 (final height), 0.5672 (final d.b.h.), and 

0.6412 (final volume per tree). 

of suppressed trees ranged from 1 to 2 percent 2 years 

after application of treatments. 

Crown damage to herbicide-treated loblolly pine 

trees in the first growing season after treatment was 

minimal (table 3). The percentage of injured trees 

decreased during the second growing season after 

treatment. Changes in pine survival after herbicide 

treatment were not significant, but mortality of pine 

saplings was greatest in the Pronone 106 treatment 

(table 4). Howwer, pine survival was poor in only one of 

the Pronone 106 plots (data not shown). Pine survival 

in the other two Pronone 106 plots was comparable to 

that for the other three treatments within each appropriate block. 

Final loblolly pine height, d.b.h., and volume per tree 

did n~t differ significantly by treatment after results 

were weighted for initial height and d.b.h. measurements (table 4). The pines on the Roundup plots grew 

least, however. Cumulative height gfovsiLh between September 1984 and April 1988 was 8.5,9.8, 10.3, and 10.3 

ft on the Roundup, Pronone 106, Velpas E, and untreated check treatments, respectively. Over the same 

period, cumulative d.b.h. growth was 2.0 inches for the 

Roundup treatment and 2.2 inches for each of the other 

treatments. 

DISCUSSION 

Broadcast application of a liquid hexazinone formulation Welpar L) caused a delayed reduction in hardmod 

stockng, whereas broadcast application of a granular 

hexazinone formulation (Pronone 106) reduced hardwood stocking in the first year after treatment. Broadcast application of a liquid glyphosate formulation 

(Roundup) reduced hardwood stocking in the first year 

after treatment. It is unclear why one hexazinone formulation would have greater early efficacy than the 
other. However, efficacies of the two hexazinone treatments did not differ significantly after two growing 

seasons. 

The proportion of free-to-grow pines in the untreated check plots increased by 17 percent over a 

2-year period. So, although herbicide release treatments may have increasd the proportion of free-togrow pines, most of this perceivd benefit might have 

occurred without management intervention. Herbicide 

injury apparently did not keep the pines from responding to release, and the few injured trees were evidently 

recovering. 

Grovvth and yield of loblolly pines did not differ significantly among treatments, but height and d.b.h. 

grovvth were somewhat less on the Roundup plots than 

on the other plots. This was the case even though the 

Roundup treatment was somewhat more effective than 

the others in controlling hardwoods. However, 

Roundup was associated with slightly more crown 

damage than were the other herbicides; 6 percent of 

the Roundup-treated pines had needle discoloration, 

needle malformation, and tip burn on the lateral 

branches in less than 50 percent of the crown after two 

growing seasons. Also, the increase in proportion of 

free-to-grow pines was slightly less for the Roundup 

treatment than for the other two herbicide treatments. None of the three aerially applied pine-release 

herbicides increased the growth and yield of planted 

loblolly pines in competition with about 1,200 hardwood trees and 4,700 shrubs per acre. 

Clason, 'Gerry R. 1984. Hardwood eradication improves 

productivity of thinned loblolly pine stands. Southern Journal of Applied Forestry. 8(4): 19P197. 

Ford-bbertson, F.C., ed. 1971. Terminology of forest 

science, technology, practice and products. Washington, DC: Society of herican Foresters. 349 p. 

Glover, Glenn R.; Dickens, Dale F. 1985. Impaet of 

competing vegetation on yield of the southern pines. 

Res. Pap. 59. AtlanLa, Gk. Georgia Forestry Commission, Research Division. 14 p. 

Waywood, James D. 1985. Vegetation management in 

young stands. In: Procdings of the 2nd annual 

Ark-La-Tex Forestry Forum; 1985 November 13; 

Shreveport, LA. Baton Rouge, LA: Louisiana Cooperative Extension Service, Louisiana State University 

Agricultural Center: 9-19. 

Haywood, James 19. 1986. Response of planted Pinus 

tueda L. to brush control in northern Louisiana. 

Forest Ecology and Management. 15: 129-134. 

Schmitt, Dan; Bower, Dave. 1970. Volume tables for 

young loblolly, slash, and longleaf pines in plantations in south Mississippi. Res. Note SO-102. New 

Orleans, LA: U.S. Department of Agriculture, Forest 

Service, Southern Forest Experiment Station. 6 p. 

Swindel, Benee F.; Marion, Wayne R.; Harris, Larry D. 

[and others]. 1983. Multi-resource effwts of harvest, 

site preparation, and planting in pine flatwoods. 

Southern Journal of Applied Forestry. 7(1): 6-15. 

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service. 

This publication reports research involving pesticides. It does not contain 

rwommendations for their use, nor does it imply that the uses discussed here 

have been registered. All uses of pesticides must be registered by appropriate 

State and/or Federal agencies before they can be recommended. 

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 rwommended practices for the 

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be report& Lo the Secretary of Agriculture, Washington, DC 20250. 
United States 

Department of Agriculture 

Forest Sewice 

Southern Forest 

Experiment Station 

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Penalty for Private Use $300 

Haywood, James D. 1993. Effects of aerially applied glyphosate and 

hexazinone on hardwoods and pines in a loblolly pine plantation. Res. 

Pap. SO-277. New Orleans, LA: U.S. Department of Agriculture, Forest Service, Southern Forest Experiment Station. 5 p. 

Three herbicide products, Roundup@ (glyphosate), Pronone@ 106 (hexazinone), and Velpar@ L (hexazinone), were applied aerially to release a 

4-year-old loblolly pine plantation from hardwood competition. Herbicide damage to pines was not excessive. Post-treatment growth of 

pines in herbicide-treated plots was not significantly different from 

growth of pines in untreated check plots. 

Ke~ords,: Competition control, pine-hardwood relationships, Pinus 

taeda L., weed control. 

*U.S. GOVERNMENT PRINTING OFFICE:1993-565-016/80035