Historic, archived document Do not assume content reflects current scientific knowledge, policies, or practices. Paciric INIoRTH Wrest FOREST AND RANGE EXPERIMENT STATION ‘USDA FOREST SERVICE RESEARCH NOTE | / / PNW-285 December 1976 a _--, __ HERBICIDES FOR GRASS AND FORB CONTROL BSW FOREST AND RANGE | PPRMPERIMENT STATION | IN DOUGLAS-FIR PLANTATIONS | ’ } | © gun14 1977 q by | STATION LIBRARY COPY H. Gratkowski , Research Forester ABSTRACT Tests of 10 chemicals were conducted to determine their relative effectiveness for grass and forb control in Douglas-fir 4 plantations. Atrazine at 4 1b ai per acre and terbacil at 2 1b ai per acre should be useful in broadcast or aerial sprays to release : small Douglas-firs. Atrazine reduced grass cover for 1 year, but had little effect on broadleaved weeds. Terbacil reduced both ' grass and forbs through two summers after application. Dalapon and a granular formulation of dichlobenil damaged the conifers but should be useful for site preparation in grass-forb communities. KEYWORDS: Herbicides, grass control, forb control, release, spraying (aerial), herbicide preparations. 7 REST SERVICE - US. DEPARTMENT OF AGRICULTURE - PORTLAND, OREGON Dense stands of grasses and broadleaved weeds prevent establish- ~ ment and retard growth of Douglas-fir seedlings on forest land in western Oregon and Washington. Shading and matting by weeds and grasses reduce survival and growth of small trees in dense grass-forb communities; however, root competition for limited soil mois- ture during the dry summer season is probably far more important. Late winter aerial application of 4 1b ai (active ingredient) of atrazine per acre has proved effective in con- trolling most grasses but is relatively ineffective against many broadleaved weeds. As a result, atrazine releases not only conifers but forbs as well. Fast-growing forbs then multiply and dominate the site, shading the trees, using valuable soil moisture, and ~ smothering small trees under a mat of dead stems and leaves when the weeds die during summer and autumn. Forest- ers need a broad-spectrum herbicide that will control most species of grasses and broadleaf weeds without damaging young conifers. HERBICIDES’ AND METHODS Ten herbicides (table 1) were tested in southwestern Oregon for grass and broadleaf weed control in three plantations of established young Douglas-firs 6 to 15 inches tall. Two study areas were on wet sites in the Siskiyou National Forest: one on the coastal slope of the Siskiyou Mountains near Brookings; one near the crest of the Coast Range west of Powers. The third area was in a Bureau of Land Management plantation on a dry site in the foothills of the Cascade Range 1/ — Use of trade, firm or corporation names is for the information and convenience of the reader. Such use does not constitute an official endorsement or approval by the U.S. Department of Agriculture of any product or service to the exclusion of others that may be equally suitable. east of Roseburg. Two additional rep- lications (without conifers) were also installed on a very dry site in the Rogue River Valley west of Grants Pass. Different rates of herbicides and combinations of herbicides provided 22 treatments on each site. All herbicides were applied on 1/100th-acre plots, and each replication contained one untreated plot for comparison. The screening test was installed as a randomized complete block experiment with one block of treatments on each of the five sites. Most of the chemicals are soil-active herbicides absorbed through roots of susceptible species. Therefore, all plots were sprayed between March 7 and April 18, 1969, when sufficient rain- fall could be expected after application to leach the chemicals into the soil, All chemicals except 2,4-D were applied as the active ingredient listed in table 1; 2,4-D was a low volatile ester formulation. All chemicals were applied in water carriers at a rate of 100 gallons of spray per acre. The wettable powder formulation of dich- lobenil was included on all five sites, but a 4 percent active ingredient granular form of dichlobenil arrived late and was only included in the Brookings, Powers, and Roseburg replications. Degree of grass control and ef- fects of the herbicides on broadleaf weeds and young Douglas-firs were ob- served on three dates. A late June 1969 examination was made to detect effects of the herbicides on annual grasses and broadleaf weeds that would die naturally during summer. This examination provided a basis for evaluating results of a second exam- ination in September 1969 which mea- sured grass and weed control at the end of the first growing season. The third examination in September 1970 determined whether any herbicides showed residual effects indicated by second year mortality of grasses or broadleaved weeds or delayed reinva- sion of the sprayed plots. it Table 1--Chemicals tested for grass and forb control in young Douglas-fir plantations tin Southwestern Oregon ACP 68-72 atrazine cacodylic acid hydroxydimethylarsine oxide chlorthiamid 2 ,6-dichlorothiobenzamide dalapon 2,2-dichloropropionic acid dichlobenil 2 ,6-dichlorobenzonitrile 4ichlobenil 2,6-dichlorobenzonitrile 2,4-D (2 ,4-dichlorophenoxy) acetic acid propazine 2-chloro-4,6 bis (isopropylamino)-s-triazine terbacil 3-tert-butyl-5-chloro-6-methyluracil During each examination, an ocular rating was made of percentage reduction in grass and broadleaved weed cover on treated plots as compared to an untreat- ed control plot and adjacent areas out- Side the spray plots. Effects of the herbicides were also observed on 15 young Douglas-firs, five on each plot in the three replications stocked with Douglas-fir seedlings. For each tree, notes were taken on whether the tree was dead or alive. If alive, an esti- mate was made of percentage of crown defoliated, damaged, and killed. RESULTS Both grass control and broadleaf weed control varied among chemicals and with rates of application. Gener- ally, first-year control was better than that achieved with residues that remained in the soil the second summer after application. pyrido(3,2-d)pyrimidine-2,4(H,3H)-dione, 3-sec butyl. 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine Wettable powder Wettable powder Liquid Granular powder Soluble powder Granular (4% ai) Wettable powder (50% ai) Liquid Wettable powder Soluble powder Grass Control By far the most effective chemi- cals at the end of the first summer were terbacil, atrazine, and dalapon in that order (table 2). Terbacil at 2 and 3 1b active ingredient per acre provided excellent grass control for two growing seasons after application. In contrast, atrazine allowed a rapid recovery of grasses when fall rains be- gan at the end of the first summer and had little or no residual effect the following year. Adding small amounts of either 2,4-D or cacodylic acid and 2,4-D to atrazine seems inadvisable; they had little effect on grasses and did not appreciably increase broadleaf weed control. Dalapon at 6.8 and 13.6 1b ai per acre produced acceptable grass control the first summer, but residues in the soil had much less effect on grasses the second summer after application. Table 2--First- and second-year control of grasses and forbs following chemical treatment during March-April 1969 Grass control Forb control Autumn Autum Autumn Autumn 1969 1970 1969 1970 Percent killed 63 8 14 2 85 10 34 2 70 5 27 13 70 6 26 4 Treatments Chemicals 1b/ acreL/ Carrier atrazine 3 ai Water atrazine 4 ai Water atrazine + 3 ai Water 2,4-D 1/2 ae atrazine + 3 ai Water cacodylic acid 1/2 ae + 2,4-D 1/2 ae ACP 68-72 2 ai Water ACP 68-72 4 ai Water ACP 68-72 6 ai Water terbacil 1 ai Water terbacil 2 ai Water terbacil 3iad! Water dalapon 6.8 ai Water dalapon 13.6 ai Water chlorthiamid 2 ai None chlorthiamid 4 al None chlorthiamid 6 ai None ropazine 4 ai Water dichlobenil WP2/ 2 ai Water dichlobenil WP 4 al Water dichlobenil WP 6 ai Water dichlobenil 643/ 2 ai None dichlobenil G4 4 ai None dichlobenil G4 6 ai None 1/ Pounds active ingredient (ai) or acid equivalent (ae). 2/ + Wettable powder. 3/ Granular. Granular dichlobenil was far more effective than the wettable powder formulation. Although first-year grass control was less than that of terbacil, atrazine, and dalapon, both the 4 and 6 1b per acre rates of granular dichlobenil appreciably reduced grass cover for two summers after application. Residual effects, the second summer, however, were not as great as those of terbacil. Chlorthiamid was not quite as effective as equal rates of granular dichlobenil. This is not surprising, since chlorthiamid is converted to dichlobenil in soils (Benyon and Wright 1972), and grass control is probably achieved as dichlobenil rather than as chlorthiamid. Un- doubtedly, some chlorthiamid is lost or degraded during conversion to dichlobenil in the soil, leaving less of the active ingredient to act on the grasses and broadleaf weeds. ACP 68-72 was less effective than the chemicals described above, although it did have some residual effect the second summer after application. De- velopment of this chemical has been discontinued by the manufacturer. Propazine was less effective than an equal amount of atrazine per acre. Grass control with propazine was appre- ciably less than that obtained with atrazine the first summer after appli- cation, and residual effects on grasses the second summer were not great enough to be of practical value. Broadleaf weed control was no better than that obtained with atrazine. Broadleaf Weed Control Terbacil , granular dichlobenil, and chlorthiamid were the only chemicals that produced potentially useful reduc- tions in forb cover. Of these, only terbacil residues produced a significant reduction the second summer after application. Terbacil is considered the only promising chemical for use where 2-year control of competitive vegetation is desired in grass-forb communities. Until registered, how- ever, terbacil cannot be used for this purpose on forest land. Conifer Damage Only atrazine and terbacil appear useful for releasing young Douglas-firs from grasses (table 3). Although the data show some damage to Douglas-fir from the 3 1b per acre rate of atrazine, most of this occurred on one tree on a dry interior valley plot. Trees sprayed with atrazine at a higher rate of 4 lb ai per acre and those treated with all rates of terbacil appeared normal, healthy, and undamaged at the end of the second summer following spraying. Newton (1969) stated that adding 2,4-D plus cacodylic acid to atrazine proved especially effective in releasing young Douglas-firs from grasses and broadleaved weeds. Adding small amounts of 2,4-D or 2,4-D plus cacodylic acid to atrazine did not damage the young firs in these tests, but their failure to appreciably in- crease broadleaf weed control does not seem to justify the increased expense. Although both atrazine and terbacil should be useful for conifer release in grass-forb communities, only atrazine is registered for coni- fer release in western Oregon and Washington; terbacil is not. Atrazine may be used only in combination with dalapon east of the Cascade Range. Terbacil is not registered for use on forest land. Table 3--Young Douglas-firs killed or damaged and degree of damage sustained by the injured trees sprayed with herbicidal chemicals during March-April, 1969 Treatment Sprayed trees Chemical 1b/acreL/ atrazine atrazine atrazine D atrazine CD ACP 68-72 ACP 68-72 ACP 68-72 terbacil terbacil terbacil dalapon dalapon chlorthiamid chlorthiamid chlorthiamid propazine dichlobenil dichlobenil dichlobenil dichlobenil dichlobenil dichlobenil RRRAAA Damaged trees 1969 1970 Sprayed trees Damaged trees Defoli- ation 44 2 SD) ae el | RT PR 10 0 0 22 11 0 1 52 3 34 21 0 0 13 0 0 33 15 5 0 0 30 1 0 17 1/ Actiye ingredient or acid equivalent as shown in table 2. 2/ Average defoliation and crown kill on the damaged trees. Both dalapon and ACP 68-72 damaged young Douglas-firs when applied as foliage sprays in these tests. Dalapon seems more suitable for site preparation rather than in broadcast sprays to release young conifers. Dalapon is the only chemical now reg- istered for use east of the Cascade Range, where it may be used for site preparation (Stewart and Beebe 1974) or as a directed spray in combination with atrazine to release conifers in Oregon, Washington, and Idaho. Interim State registrations permit broadcast and aerial application of Dowpon\ M plus atrazine mixtures as foliage sprays only west of the crest of the Cascade Range in Oregon and Washington. This registered combination of dalapon and atrazine has proved useful in western Oregon and Washington. Newton and Overton (1973) reported that foliage sprays of dalapon injured young Douglas-firs and grand firs (Abtes grandis (Dougl.) Lindl.). Dalapon, however, at rates of 4 to 12 lb per acre did not injure the trees when combined with atrazine and low volatile esters of 2,4-D at rates of 3 and 4 1b per acre, respectively. Newton recently indicated that use of cacodylic acid is no longer recommended in herbicidal mixtures to be applied as foliage sprays on young conifers; rates * 1 1b per acre injure the trees2/, Dichlobenil and _ chlorthiamid caused some second-year defoliation of Douglas-fir seedlings. Considering its greater effect on broadleaf weeds and 2-year control of grasses, however, granular dichlobenil may prove a use- ful chemical for site preparation on sites occupied by mixed stands of grasses and broadleaf weeds. In England, a granular formulation of chlorthiamid is registered for release of trees from grasses and forbs, al- though Allen (1966) reported injury 2/ — Personal communication, August 1976. and mortality in conifers treated with 5 to 8 1b ai of chlorthiamid per acre. Chlorthiamid is not registered for forest use in the United States. SUMMARY Atrazine and terbacil proved the most useful chemicals for grass con- trol and conifer release in these tests. Foliage sprays of both chemi- cals controlled grasses without per- manent damage to Douglas-fir seedlings. For many years, atrazine at 4 1b ai per acre has proved effective in releasing young conifers from grasses without damaging the trees, but it is effective for only one summer and does not control broadleaf weeds. Terbacil at 2 1b ai per acre appears promising as an alternative. Although this chemical damaged a few firs during the first summer after spraying, no trees were killed and all were healthy and vigorous at the end of the second summer. Granular dichlobenil at 4 to 6 1b ai per acre also controlled grasses and forbs for two summers but produced persistent damage on young Douglas- firs. Dichlobenil seems potentially more useful for site preparation than for conifer release on sites occupied by grasses and broadleaf weeds. Be- cause of persistent damage through the second summer, reforestation would probably have to be delayed until at least three summers elapse after application. By that time, however, grass and broadleaf weed control may not be sufficient to favor the conifers; benefits may not warrant the expenditure. LITERATURE CITED Allen, M. G. 1966. Experiments with 2,6-dichlorothiobenzamide (chlorthiamid) in planted areas of soft and hardwoods. Proc. 8th Brit. Weed Control Conf., p. 135-140. (Cited from Weed Abstr. 16(2): 511.) Beynon, K. I., and A. N. Wright. 1972. The fate of the herbicides chlorthiamid and dichlobenil in relation to residues in crops, soils, and animals. Residue Rev. 43: 23-53. Newton, M. 1969. Herbicide interaction in reforestation grass sprays. im 1969) Res. Prog. Rep., West. Soc. Weed Sci., p..23-30. Newton, M., and W. S. Overton. 1973. Direct and indirect effects of atrazine, 2,4-D, and dalapon mixtures on conifers. Weed Sci. 21(4): 269-275. Stewart, R. E., and T. Beebe. 1974. Survival of ponderosa pine seedlings following control of competing grasses. Proc. West. Soc. Weed Sci. 27: 55-58. PESTICIDE PRECAUTIONARY STATEMENT Pesticides used improperly can be injurious to man, animals, and plents. Follow the directions and heed all precautions on the labels. Store pesticides in original containers under lock and key--out of reach of children and animals--and away from food and feed. Apply pesticides so that they do not endanger humans, livestock, crops, beneficial insects, fish, and wildlife. Do not apply pesticides when there is danger of drift, when honey bees or other pollinating insects are visiting plants, or in ways that may contaminate water or leave illegal residues. Avoid prolonged inhalation of pesticide sprays or dusts; wear protective clothing and equipment if specified on the container. If your hands become contaminated with a pesticide, do not eat or drink until you have washed. In case a pesticide is swallowed or gets in the eyes, follow the first-aid treatment given on the label, and get prompt medical attention. If a pesticide is spilled on your skin or clothing, remove clothing immediately and wash skin thoroughly. Do not clean spray equipment or dump excess spray material near ponds, streams, or wells. Because it is difficult to remove all traces of herbicides from equipment, do not use the same equipment for insecticides or fungicides that you use for herbicides. Dispose of empty pesticide containers promptly. Have them buried at a sanitary land-fill dump, or crush and bury them in a level, isolated place. NOTE: Some States have restrictions on the use of certain pesticides. Check your State and local regulations. Also, because registrations of pesticides are under constant review by the Federal Environmental Protection Agency, consult your county agricultural agent or State extension specialist to be sure the intended use is still registered. Ye Pestecided FOLLOW THE LABEL U.S. DEPARTMENT OF AGRICULTURE. GPO 997-643