Dalapon (2,2-dichloropropionic acid), injurious to Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) and grand fir (Abies grandis (Dougl.) Lindl.) when used alone for weed control, was used with safety and even with beneficial effects when combined with atrazine [2-chloro-4-(ethylamine)-6-(isopropylamino)-s-triazine] and 2,4-D, [(2,4-dichlorophenoxy) acetic acid] at rates of up to 3.36 and 4.48 kg/ha, respectively. Harmful effects of dalapon were masked at rates up to three times those used for adequate control of grasses. This suggests a type of selectivity previously unreported. Interpretation of herbicide effects and interactions was made possible with an analytical model that separated effects of vegetation from those of herbicides on a causal basis. This technique included two-dimensional adjustment of the base of reference for a four-dimensional response-surface equation. This surface fit observed data as well as a single multiple-regression equation, which included all variables. This approach, however, estimated herbicide parameters with appropriate consideration of environmental data and permitted interpretation with respect to cause.

Greenhouse studies were conducted to evaluate the activity of fluometuron [1,1-dimethyl-3-(α-α-α-trifluoro-m-tolyl)urea] and disulfoton [o,o-diethyl s-(ethylthio ethyl) phosphorodithioate] alone and in combination on the height of seedling cotton (Gossypium hirsutum L.) in 10 light-textured soils from the lower alluvial floodplain of the Mississippi River. An antogonistic interaction was demonstrated between the two pesticides in six of the soils studied. The phytotoxic effects of high rates of fluometuron applied preemergence were decreased by granular application of disulfoton. This interaction was repeated in four of the soils and was modified but not eliminated by partial sterilization of the soils, by autoclaving, or by fumigation before treatment. Correlation analyses detected no significant association between the antagonistic interaction and any measurable soil property in the 10 soils. Three field studies failed to demonstrate this interaction. Neither the greenhouse nor the field studies revealed any deleterious interaction between these two chemicals.

Ten commercial soybean [Glycine max (L.) Merr.] cultivars were evaluated for reaction to over-the-top applications of two rates of 3′,4′-dichloropropionanilide (propanil) at the growth stage when three nodes on the main stem had completely unrolled leaves. Propanil, a herbicide commonly applied to rice [Oryza sativa L.] for control of grass weeds, was applied at 0.56 and 3.36 kg/ha; the higher rate is commonly used for control of weeds in rice. ‘Davis’, ‘Hood’, and ‘York’ soybean cultivars were damaged more by propanil than ‘Hill’, ‘Lee’, ‘Lee 68’, ‘Pickett’, ‘Semmes’, ‘Bragg’, or ‘Dare’ when damage was measured by reductions in seed yield and stand and by leaf injury.

Gamma radiation of 3 megarads was applied to undiluted commercial formulations and aqueous solutions of 3-(3,4 dichlorophenyl)-1,1-dimethylurea (diuron), 1,1-dimethyl-(3-a,a,a-trifluoro-m-tolyl)-urea fluometuron), N,N-dimethyl-2,2-diphenylacetamide (diphenamid), 2,4-bis (isopropylamino)-6-(methylthio)-s-triazine (prometryne), dimethyl tetrachloroterephthalate (DCPA), a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) and sodium chlorate. The effect of radiation on herbicidal activity was assessed with bioassays. Radiation did not affect the bioactivity of undiluted or 50% solutions of any of the tested herbicides but decreased appreciably the activity of 100-ppm solutions of fluometuron, diphenamid, and prometryne. Diluted 100 and 10-ppm solutions of trifluralin lost part of their activity during storage in plastic containers and, in addition, following irradiation. It was not clear whether the decrease in activity observed in the 100-ppm solution of diuron was due to irradiation or to storage. No reduction in bioactivity was produced following irradiation of 100 and 10-ppm solutions of DCPA or 1% and 10% solutions of sodium chlorate.

Analysis of soil samples taken periodically from field plots on Dundee silty clay loam treated with single or dual annual applications of 4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline (nitralin) or α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) at 0.84 or 1.68 kg/ha indicated dissipation of the herbicides to a low residual level within 3 to 4 months following each application. No accumulation was noted with either herbicide regardless of frequency or rate of application. Nitralin phytotoxicity to sorghum (Sorghum bicolor L. ‘Dekalb 57E’) decreased more rapidly in soil that had received prior treatment with nitralin than in soil with no previous treatment. A microbiological influence is suggested because this effect was nullified by autoclaving the soil prior to herbicide treatment. This effect was not apparent with trifluralin. A survey of 250 fields indicated a significant, inverse correlation between nitralin and trifluralin residue level and soil pH. Nitralin persistence was greater in acid than in neutral soil.

The root growth rate index of velvetleaf (Abutilon theophrasti Medic.) was significantly greater than that of five other weed species. The root growth rate index of sorghum [Sorghum bicolor (L.) Moench ‘RS-626’] was found to be significantly higher than that of soybeans [Glycine max (L.) Merr. ‘Ford’]. Shoot growth rate indexes of three perennial broadleaf species studied were significantly lower than shoot growth rate indexes of six annual species. Root weights of perennial broadleaf species were not significantly different from root weights of velvetleaf and soybeans. Soybeans were found to have a significantly higher shoot to root ratio than seven weed species but not higher than sorghum. All other species had larger leaf weights and leaf areas than the three broadleaf perennials. While there were significant differences in leaf weights among six species, there were no significant differences in leaf area. Seed weight was not significantly correlated with emergence rate index and root weight but was correlated to all other factors studied. Emergence rate index was correlated with root growth rate index but not with shoot growth rate index.

In growth room studies, N,N-diallyl-2,2-dichloroacetamide (hereafter referred to as R-25788) was the most effective of three antidotes for the reduction of EPTC (S-ethyl dipropylthiocarbamate) injury to corn (Zea mays L. ‘United Hybrid 106’). R-25788 reduced EPTC injury to corn as a seed treatment, as an incorporated soil spray, or in nutrient solution in quartz sand nutrient culture. CDAA (N,N-diallyl-2-chloroacetamide) was also an EPTC antidote for corn when applied to the soil or in nutrient solution but was itself toxic to corn when applied as a seed treatment. The antidote 1,8-naphthalic anhydride (hereafter referred to as naphthalic anhydride) was less effective than R-25788 as a seed treatment and was ineffective when applied to the soil. Naphthalic anhydride was the only one of the three antidotes which also reduced EPTC toxicity to green foxtail [Setaria viridis (L.) Beauv.].

Twelve-day-old corn seedlings (Zea mays L. ‘Funk's G-83’) were exposed to thermal conditions (482 C for 125 msec) approximating those used for flame weed control. Tissue dehydration was evident within 1 min after flame application. One hour after flame exposure, the water content of shoot tissues was 6% less than in nonflamed shoots. Transpirational water loss 16 hr after flame application was reduced by 68% when compared to that of nonflamed seedlings. Assimilation of 14CO2 by flamed seedlings, while substantially decreased when compared with that of nonflamed seedlings, continued on a limited basis even in the most severely injured leaf tips.

Corn (Zea mays L. ‘Funk's G-83’) seedling leaves exposed to flame-generated ultra-high temperatures produced in flame cultivation were fixed in glutaraldehyde, post fixed in osmium tetroxide, and embedded in Araldite. In the light microscope, bundle sheath cells of flamed tissue were more heavily stained with Azure II and less vacuolated than were nonflamed cells. Heated mesophyll cells contained swollen, disrupted, and granular chloroplasts. Examination of flamed tissue by electron microscopy revealed granular, dispersed cytaplasm and altered membrane systems. Chloroplast lamellar systems and envelopes, tonoplasts, and plasmalemmas were disintegrated in both bundle sheath and mesophyll cells.

An endemic anthrocnose disease of northern jointvetch [Aeschynomene virginica (L.) B.S.P.] incited by the fungus Colletotrichum gloeosporioides (Penz.) Sacc. f. sp. aeschynomene was discovered in 1969 at Stuttgart, Arkansas. When grown on solid or in liquid media, the organism grew rapidly and sporulated abundantly. From 1970 through 1972 water sprays of the fungus spores at 2 to 15 million spores per milliliter in 94 to 374 L/ha controlled northern jointvetch grown in the growth chamber, greenhouse, and field. The fungus controlled plants ranging from 5 to 66 cm tall. The disease developed on northern jointvetch most rapidly at temperatures of 23 to 32 C and at relative humidities above 80%. An incubation period of 4 to 7 days and up to 5 weeks was usually required to kill the weeds. The fungus was specific for Aeschynomene species since it was very virulent on A. virginica and only slightly virulent on Indian jointvetch (A. indica L.). It did not affect rice (Oryza sativa L.), soybeans [Glycine max (L.) Merr.], cotton (Gossypium hirsutum L.), or 12 other common field, forage, and vegetable crops or 15 common weeds.

Tolerance of greenhouse-grown soybean (Glycine max (L.) Merr.) to preemergence applications of 4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)one (metribuzin) was greatly influenced by herbicide rate, soil organic matter, and simulated rainfall after treatment. Planting depth affected tolerance in cases where effects of the other variables were marginal. Severe injury was observed with 1.1% soil organic matter except at the 0.56 kg/ha herbicide rate with no rainfall for 10 days after treatment. Tolerance increased with increasing soil organic matter to the point where no injury occurred at 16.8 or 40.0% organic matter, even at herbicide rates up to 1.68 kg/ha with 1.25 cm simulated rainfall immediately after treatment.

Fumitory (Fumaria officinalis L.) achenes were after-ripened in moist sand at 4 C for 0, 15, 30, 45, and 60 days. Embryo size in longitudinal section increased 14 times during after-ripening. The percentage of ether soluble lipids and their fatty acids remained constant during the entire after-ripening period. Soluble carbohydrates were the highest at the 45-day period of after-ripening when embryo growth was rapid. The concentration of 70% ethyl alcohol soluble amino acids increased gradually over the first 45 days of after-ripening and decreased over the last 15 days as embryo growth became more rapid.

Degradation of SAN 6706 [4-chloro-5-(dimethylamino)-2-(α,α,α-trifluoro-m-tolyl)-3(2H)-pyridazinone] and SAN 9789 [4-chloro-5-(methylamino)-2-(α,α,α-trifluoro-m-tolyl)-3 (2H)-pyridazinone] was studied in a sandy loam soil at temperatures of 5, 20, and 35 C. After 210 days of incubation 10, 80, and 97% of SAN 6706 had been dissipated from soil at 5, 20, and 35 C., respectively. SAN 6706 was converted to SAN 9789 and a demethylated metabolite in the soil. SAN 9789 was converted to the demethylated metabolite. It was difficult to differentiate between first and second-order kinetics in the degradation of these compounds. SAN 6706, at 20 and 35 C, had a half life of 50 and 9 days respectively, and an Arrhenius activation energy of 15.8 Kcal/mole. SAN 9789, at 20 and 35 C, had a half life of 270 and 70 days, respectively, and an activation energy of 11.8 Kcal/mole. The degradation of SAN 6706 was inhibited by a chloroform treatment, and microbiological degradation is suggested.

Fenac [(2,3,6-trichlorophenyl)acetic acid] and its sodium salt were incorporated in polyethylene matrices under varied conditions to afford a series of herbicide-polyethylene formulations. Diffusion within the matrix determined the rates at which the herbicides were released from the formulations into water. Release rates of the herbicides were altered significantly if (a) the formulation curing conditions were varied, (b) the initial amount of herbicide in the matrix was varied, (c) the solubility of the herbicide was changed, or (d) if an additive was used. The results indicate that herbicide diffuses from the matrix through water-filled cracks and capillary channels.

Seeds of five crop and 17 weed species were germinated with 0, 3, 6, and 10-bar water solutions of polyethylene glycol to simulate drought. With simulated drought, most weed species germinated better than soybeans (Glycine max L. ‘Hampton 266A’) but were not equal to pearlmillet [Pennisetum typhoides (Burm.) Stapf. and C. E. Hubb ‘Millex 23’] or sorghum-sudangrass [Sorghum bicolor (L.) Moench x S. sudanense (Piper) ‘SX-16’]. Prickly sida (Sida spinosa L,), sicklepod (Cassia obtusifolia L.), and Ipomoea lacunosa L. were the most tolerant weed species to simulated drought. Four species were intermediate in tolerance and four species germinated poorly under simulated drought. Hemp sesbania [Sesbania exaltata (Raf.) Cory] was the least tolerant and was similar to soybean.

Annual weeds were allowed to compete until or after each of the first three postemergence irrigations of furrow-irrigated cotton (Gossypium hirsutum L. ‘Deltapine 16’). Beds and furrows were shaped with a sectioned, rolling cultivator three times between cotton emergence and the second irrigation. Cotton boll components and fiber properties were not affected by periods of competition with annual weeds. Weeds allowed to compete after the first or second irrigations significantly reduced the 4-year average yield of cotton by 16 and 12%, respectively. Competition that began after the third or fourth irrigation, or that ended after the first, second, or third irrigation was less detrimental and did not significantly affect yields.

Seven herbicides were evaluated for the control of yellow nutsedge (Cyperus esculentus L.) in cotton (Gossypium hirsutum L. ‘Acala SJ-1’) in three field experiments during 1970 and 1971. The herbicides, 2-chloro-2′,6′-diethyl-N-(methoxymethyl) acetanilide (alachlor); 2-chloro-2′,6′-diethyl-N-(butoxymethyl) acetanilide (CP-53619); 2,4-bis(isopropylamino)-6-methylthio)-s-triazine (prometryne); 2-(α-naphthoxy)-N, N-diethylpropionamide (R-7465); S-isopropyl 5-ethyl-2-methylpiperidine-1-carbothioate (R-12001); 4-chloro-5-(dimethylamino)-2-(α,α,α-trifluoro-m-tolyl)-3-(2H)-pyridazinone (San-6706); and 2-(3,4-dichlorophenyl)-4-methyl-1,2,4-oxadiazolidine-3,5-dione (methazole), were applied broadcast and incorporated 10 cm deep into the soil before the preplanting irrigation. All herbicides controlled nutsedge for at least 1 month in two or more experiments. Cotton was most tolerant to applications of 2.24 and 4.48 kg/ha of CP-53619, 3.36 and 6.72 kg/ha of prometryne, 1.12 kg/ha of San-6706, and 2.24 kg/ha of methazole. Higher rates of San-6706 and methazole and all rates of alachlor, R-7465, and R-12001 reduced the yield of cotton in one or more experiments.

The combination of the herbicide 2-chloro-2′,6′ diethyl-N-(methoxymethyl) acetanilide (alachlor) with the insecticide 2,2-dimethyl-2,3-dihydrobenzofuranyl-7-N-methyl-carbamate (carbofuran) interacted synergistically to reduce barley [Hordeum vulgare L. ‘Larker’] but not corn [Zea mays L. ‘Michigan 400’] growth. Alachlor alone increased the respiration rate of barley. Accumulation of 14C from 14C-alachlor was greater in the plant roots than shoots. The increased accumulation of alachlor in the roots was accentuated by a reduced rate of alachlor metabolism. The basis for the observed interaction appeared to be greater alachlor uptake by barley plants grown from seed treated with carbofuran. A statistical procedure for pesticide combinations in experiments with a completely randomized design was developed for the calculation of interaction significance.

Treatments with the herbicide 3-(4-bromo-3-chlorophenyl)-1-methoxy-1-methylurea (chlorbromuron) were combined with seed treatments with the insecticide, 2,2-dimethyl-2, 3-dihydrobenzofuranyl-7-N-methylcarbamate (carbofuran), to measure phytotoxic interaction effects on barley (Hordeum vulgare L. ‘Larker’) and corn (Zea mays L. ‘Michigan 400’). The combination synergistically reduced radicle length in barley seedlings and reduced the leaf area and dry weight of 7-day-old corn seedlings grown in sand culture. The chlorbromuron-carbofuran combination reduced net photosynthesis in barley and corn and increased respiration in barley. The 14C from 14C-chlorbromuron preferentially accumulated in barley and corn shoots. The carbofuran seed treatment resulted in a reduced level in barley shoots and corn roots but increased the accumulation of 14C in barley roots and corn shoots. The basis for this interaction appeared related to the increased accumulation of chlorbromuron in corn and barley shoots and reduced chlorbromuron metabolism.

Radicle length of barley (Hordeum vulgare L. ‘Larker’) seedlings was greatly reduced by the combination of the herbicide S-ethyl diisobutylthiocarbamate (butylate) applied in combination with the insecticide 2,2-dimethyl-2,3-dihydrobenzofuranyl-7-N-methylcarbamate (carbofuran). Corn (Zea mays L. ‘Michigan 400’) seedlings were not similarly affected. Carbofuran interacted with butylate to reduce synergistically the root and shoot growth of barley but not that of corn. The combination of these two carbamate pesticides synergistically increased respiration in barley. The basis for these interaction effects in barley appeared to be decreased metabolism of butylate and increased respiration in the presence of carbofuran. Although the same metabolism trend was apparent in tolerant corn, the butylate level was much lower since the absorption of butylate was reduced by the carbofuran seed treatment. The 14C from 14C-butylate preferentially accumulated in barley shoots and corn roots.