One greenhouse and two field experiments were conducted to determine if crop protectants used in conjunction with herbicides would permit weed-free establishment of orchardgrass (Dactylis glomerata L. ‘Potomac’) with alfalfa (Medicago sativa L. ‘WL 307’). Herbicides used were EPTC (S-ethyl dipropylthiocarbamate) and butam [2,2-dimethyl-N-(1-methylethyl)-N-(phenylmethyl)propanamide] plus cyprazole {N-[5-(2-chloro-1,1-dimethylethyl)-1,3,4 thiadiazol-2-yl] cyclopropanecarboxamide}. These experiments revealed that banded activated charcoal allowed limited orchardgrass establishment with a herbicide but did not result in consistently better orchardgrass stands than the untreated control. Orchardgrass was not protected from herbicide injury by 1,8-naphthalic anhydride (NA) or R-25788 (N,N-diallyl-2,2-dichloroacetamide). The butam plus cyprazole mixture consistently controlled grass and broadleaf weeds as effectively as EPTC.

In greenhouse studies, soil applications of 14C-methyl-labeled glyphosate [N-(phosphonomethyl)glycine] were not readily absorbed by corn (Zea mays L. ‘Michigan 400’) and soybean [Glycine max (L.) Merr. ‘Hark’]. However, glyphosate available to plants in sand culture was absorbed. Wheat (Triticum aestivum L. ‘Avon’) a sensitive bioassay plant, was used to detect the herbicide. Clay loam and muck soil rapidly inactivated 56 kg/ha of glyphosate. Autoclaving of the soil did not prevent the inactivation of glyphosate. In a sandy clay loam soil, application of 56 kg/ha of glyphosate decreased plant growth with increasing pH. Additions of 98 or 196 kg/ha of phosphate to the soil surface decreased glyphosate inactivation in the soil. It is postulated that initial inactivation of glyphosate in soil is by reversible adsorption to clay and organic matter through the phosphonic acid moiety.

Butylate (S-ethyl diisobutylthiocarbamate), EPTC (S-ethyl dipropylthiocarbamate), vernolate (S-propyl dipropylthiocarbamate), diallate [S-(2,3-dichloroallyl)diisopropylthiocarbamate], CDEC (2-chloroallyl diethyldithiocarbamate), and chlorpropham (isopropyl m-chlorocarbanilate) at 0.1 kg/ha caused increased velvetleaf (Abutilon theophrasti Medic.) populations in field plots. Butylate caused increased populations of common lambsquarters (Chenopodium album L.) at rates of up to 1.1 kg/ha. In the laboratory, each of the six herbicides caused increased velvetleaf seed germination, and butylate, EPTC, and CDEC caused increased common lambsquarters germination when seeds were exposed to herbicide vapors prior to germination. Germination of velvetleaf, common lambsquarters, and giant foxtail (Setaria faberii Herrm.) was also increased by butylate solutions over a wide range of concentrations. Maximum germination stimulation generally occurred between concentrations of 10-5 and 10-6 M butylate. Seedling injury and death also resulted from these concentrations of butylate. Butylate stimulation of seed germination could not be correlated with light requirements of seeds, but appeared to be an additional promotive factor. Ungerminated common lambsquarters seeds after butylate treatment were viable and responded to KCN and KNO3 in the same manner as control seeds which did not initially germinate in water. Butylate in combination with the antidote, R-25788 (N,N-diallyl-2,2-dichloroacetamide) stimulated germination of common lambsquarters.

Tolerance of corn (Zea mays L.) to cyanazine {2-[[4-chloro-6-(ethylamino)-s-triazin-2-yl] amino]-2-methylpropionitrile} and atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] was compared when grown in Conover sandy loam soil. Reductions in seedling dry weight were obtained under both low and high soil moisture following preemergence and postemergence applications of cyanazine allowed to contact both plants and soil. During periods of active plant growth high soil moisture is favorable for rapid root uptake of cyanazine which causes injury to corn.

Preplanting applications of diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] with and without trifluralin (a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) were made for 5 years in irrigated cotton (Gossypium hirsutum L.). All treatments containing trifluralin temporarily stunted cotton. In two of the 5 years, trifluralin reduced diuron injury to cotton seedlings which resulted in better crop stands. The trifluralin-diuron combinations resulted in better weed control at harvest than either herbicide alone. The 5-year average yield of cotton was greater with trifluralin-diuron combinations than with the same rates of diuron alone.

Glyphosate [N-(phosphonomethyl)glycine] was readily bound to kaolinite, illite, and bentonite clay and to charcoal and muck but not to ethyl cellulose. Fe+++ and Al+++-saturated clays and organic matter adsorbed more glyphosate than Na+ or Ca+-saturated clays and organic matter. Glyphosate appears to be bound to the soil through the phosphonic acid moiety as phosphate in the soil competed with 14C-glyphosate for adsorption sites. Glyphosate mobility in the soil was very limited and was affected by pH, phosphate level, and soil type. The 14C-glyphosate was biodegraded in soil to 14CO2 possibly by co-metabolism. Potentiometric titrations of the compound gave pKa values of 2, 2.6, 5.6, and 10.6.

MSMA (Monosodium methanearsonate) applied postemergence at 4.5, 6.7, or 9.0 kg/ha controlled wild oat (Avena fatua L.) in new plantings of Kentucky bluegrass (Poa pratensis L. ‘Pennstar’) and in perennial ryegrass (Lolium perenne L. ‘Reveille,’ ‘Pennfine’). MSMA at 4.5 kg/ha was almost as effective as the higher rates in controlling wild oat. MSMA at 2.2 kg/ha was less effective in some experiments. Visual injury to the perennial grasses was negligible. Satisfactory grass stands developed at all MSMA rates. Perennial ryegrass seed yields were higher than the untreated check in most experiments when MSMA was applied at 4.5, 6.7, or 9.0 kg/ha before the grass reached the boot stage. When MSMA was applied after the ryegrass reached the boot stage, some of the treatments reduced ‘Reveille’ perennial ryegrass seed production.

Radioactive glyphosate [N-(phosphonomethyl)glycine] is rapidly absorbed with a large portion of the 14C translocated to the rhizomes and untreated shoots of quackgrass [Agropyron repens (L.) Beauv.]. The adjuvant used with glyphosate was important in determining its phytotoxicity to quackgrass. In other perennial weeds and annual species, glyphosate also moved to the areas of highest metabolic activity. In Canada thistle [Cirsium arvense (L.) Scop.], bentazon (3-isopropyl-1H-2,1,3-benzothiadiazin-(4) 3H-one 2,2-dioxide) at 2.24 kg/ha applied prior to treatment with 14C-glyphosate reduced 14C translocation. Iron or nitrilotriacetic acid (NTA) did not appear to effect glyphosate activity on wheat (Triticium aestivum L. ‘Avon’). The respiration of quackgrass treated with glyphosate was significantly reduced 9 days after treatment. Glyphosate reduced total photosynthesis more in quackgrass than in wheat.

Inhibition of seedling growth and four assays for inhibition of photosynthesis were used to compare karbutilate [tert-butylcarbamic acid ester with 3-(m-hydroxyphenyl)-1,1-dimethylurea] with derivatives of karbutilate in which either the urea or carbamate side chain was missing. Karbutilate was a more potent, more presistent, and more specific inhibitor of photosynthesis than the phenylurea derivative fenuron (1,1-dimethyl-3-phenylurea) that would be formed by removal of the carbamate side chain. However, karbutilate did not exert the growth-inhibiting action observed for the alkyl carbamate derivative phenyl-N-tert-butylcarbamate, formed by removal of the urea side chain, which does not affect photosynthesis at concentrations below 10-3 M.

The effect of time, flow rate, and temperature on the volatilization of technical grade n-butyl ester of 2,4-D [(2,4-dichlorophenoxy)acetic acid] in a closed air-flow system was evaluated. The amount of ester volatilized was linear with time, at constant temperature and air flow. Volatility increased approximately 8-fold when the temperature was increased from 30 C to 50 C. At 30 C, volatility increased with each doubling of air flow rate from 0.86 nmole/cm2 per hr at 14 L/hr to 1.62 nmole/cm2 per hr at 57.6 L/hr. The effects of temperature, flow rate, and the relationship between vapor pressure and rate of volatilization were also analyzed. The system provided a simple and quantitative method for determining the relative volatilities of both technical and formulated herbicides.

The response of corn (Zea mays L.) and fall panicum (Panicum dichotomiflorum Michx.) to postemergence herbicide applications at three stages of growth was examined. Early postemergence application of cyanazine 2-[[4-chloro-6-(ethylamino)-s-triazine-2-yl] amino]-2- methylpropionitrile at 3.4 kg/ha provided the best control with minimum crop injury and greatest corn yield. A reduction of 25% in corn yield resulted when fall panicum was removed by hand at the seven to eight-leaf stage as compared to removal of plants with two leaves. Various adjuvants increased cyanazine action on both fall panicum and corn in field and greenhouse experiments; however, field trials showed no differences in grain yield at harvest. In the greenhouse, less corn injury was observed with a vegetable oil additive than with other adjuvants.

CBC (2,5-dichlorobenzoyl chloride) and MCB (methyl-2,5-dichlorobenzoate) function as plant growth regulators in a gaseous phase or in an aqueous solution. Sorghum [Sorghum bicolor (L.) Moench. ‘Martin’] and soybean [Glycine bicolor (L.) Merr. ‘Lee’] seeds were temporarily inhibited or delayed from germinating, but overcame the inhibition in time so there was no significant reduction in total germination. Seedlings produced from sorghum and soybean seed germinated and grown in aqueous solution of 35 μg/ml CBC or MCB were shorter and weighed less than control seedlings. Soybean seed treated with the vapors of CBC and MCB produced seedlings significantly reduced in dry weight as compared with that of controls. Foliar application of 500 or 1000 μg/ml of CBC significantly reduced the growth of soybean but not sorghum seedlings. Soybean seedlings treated with the vapors or an aqueous solution produced leaflets more narrow and thicker than control seedlings. A lethal response attributable to CBC or MCB was not recorded.

Ethylene gas (C2 H4) was found to stimulate the germination of witchweed [Striga asiatica (L.) O. Kuntze] seeds. Ethylene diffuses greater than 120 cm horizontally from point of injection and more than 90 cm below the soil surface. Rates of 0.42 kg/ha induced germination of witchweed seeds in sandy soil; but 1.1 kg/ha is required on a heavy clay soil. Witchweed seeds respond to ethylene after a period of preconditioning that is necessary to break dormancy. Under field conditions in the Carolinas, maximum response of seeds to ethylene occurs between late April and late July. Field studies indicate a 90% reduction in viable witchweed seeds occurs where a single treatment with ethylene has been applied. The use of ethylene appears now to be a major contributor toward the eventual eradication of witchweed from the United States.