Leaves absorbed high amounts of clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) as foliar sprays on honey mesquite (Prosopis glandulosa Torr. # PRCJG) as indicated by concentrations of 10 μg/g fresh wt or more in basal stem phloem by 4 days after treatment. Small quantities of clopyralid (< 1 μg/g) were detected in basal stem phloem after spray applications of clopyralid to defoliated plants or roots treated by soil application. When applied to foliated plants, the 0.56 kg/ha of clopyralid killed 60% or more plants, but none were killed when clopyralid sprays were applied to defoliated plants or when 2.2 kg/ha of clopyralid was applied to the soil. Water, diesel oil plus water, or water plus surfactant were equally effective as clopyralid carriers as foliar sprays.

In laboratory and field studies, quackgrass (Agropyron repens (L.) Beauv. # AGRRE) was subjected to postemergence applications of the butyl ester of fluazifop-P {(R)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid}, methyl ester of haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid}, or ethyl ester of quizalofop {2-[4-[[6-(chloro-2-quinoxalinyl)oxy] phenoxy] propanoic acid}. Haloxyfop, fluazifop-P, and quizalofop each required a minimum of 1 week to reduce quackgrass transpiration or water uptake in the laboratory. At rates lower than 0.56 kg ae/ha, fluazifop-P reduced quackgrass transpiration and water usage less quickly and to a lesser extent than equivalent rates of haloxyfop and quizalofop. The time required for significant transpiration and water uptake reduction by herbicide-treated quackgrass was several days longer in the field than in the laboratory, but the reaction patterns among the herbicides were similar. Little if any benefit was obtained from sequential applications of the herbicides compared with single applications of the same total dosage. All three herbicides significantly reduced quackgrass dry weight.

The effects of caffeic, vanillic, p-coumaric, chlorogenic, and ferulic acids, ragweed parthenium (Parthenium hysterophorus L. # PTNHY) residue and extracts on the growth, ion uptake, and chlorophyll content of 3-week-old tomatoes (Lycopersicon esculentum Mill. ‘Walter’) grown in the greenhouse were determined Vanillic, p-coumaric, chlorogenic, and ferulic acid at 10−3 M and parthenium extract at 0.5% (w/v) significantly reduced tomato root and shoot dry weight. Ragweed parthenium residue at 0.5% (w/w) and extract at 0.5% (w/v) significantly reduced tomato shoot and root dry weight. Leaf nitrogen content was reduced by phenolic acids (10−3 M) and ragweed parthenium extract (0.5%). Phosphorus content was reduced by all phenolic acids at 10−3 M and ragweed parthenium extract at 0.5% (w/v). In addition, p-coumaric and ferulic acids at 10−4 M reduced phosphorus content. No consistent relationship between chlorophyll content and tomato growth reduction was observed.

The influence of various additives on CGA-82725 [2-propanyl-2,4-(3,5-dichloro-2-pyridyloxy)phenoxy propanoate] absorption and translocation was determined in oats (Avena sativa L. ‘Lyon’). The absorption and translocation of 14C was greater when 14C-CGA-82725 was applied with petroleum oil compared to soybean [Glycine max (L.) Merr.] oil. The translocation of 14C was greater at 96 than 48 h after 14C-CGA-82725 application. The absorption of 14C was greater at 48 than 24 h but was similar at 48 and 96 h after 14C-CGA-82725 application with no additive, petroleum oil, or soybean oil. The absorbed and translocated 14C was greater when 14C-CGA-82725 was applied with oil at 1.2 compared to 0.6 L/ha. No additional increase in 14C absorption and translocation was obtained if the oil volume was increased to 2.3 L/ha. The addition of petroleum oil to 14C-CGA-82725 increased 14C absorption and translocation more than the addition of palm (Eleais quineeneis Jalq.), safflower (Carthamus tinctorius L.), linseed (Linum usitatissimum L.), or soybean oil. The four seed oils and the emulsifier At Plus 300F caused similar increases in 14C absorption and translocation over 14C-CGA-82725 applied alone. Ethylene glycol did not increase 14C absorption and translocation compared to 14C-CGA-82725 applied alone.

The antagonism of the methyl ester of haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy propanoic acid} by bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one-2,2-dioxide] was evaluated through studies of absorption and translocation in yellow foxtail [Setaria lutescens (Weig. ex Stuntz.) Hubb. # SETLU]. Leaf penetration of haloxyfop was reduced 37% in the presence of bentazon. Bentazon had no effect on translocation from the treated leaf. Direct chemical interactions and contact activity by bentazon do not account for the reduced uptake of haloxyfop. Experimental evidence shows the benzothiadiazione structural class of chemistry to be general antagonists of absorption for foliarly applied herbicides.

Greenhouse studies were conducted to determine the influence of glyphosate [N-(phosphonomethyl)glycine] and surfactant concentration on Canada thistle [Cirsium arvense (L.) Scop. # CIRAR] control. Five, 10, and 30% (v/v) solutions of the commercial formulation of glyphosate (356 g ae/L glyphosate and 178 g ai/L MON 0818) applied in 2-μl droplets to Canada thistle leaves at an equal dose per plant did not reduce plant growth, whereas a 2.5% solution reduced growth by 76%. Varying the glyphosate and the polyethoxylated tallow amine surfactant (MON 0818) concentrations independently showed that low glyphosate and MON 0818 concentrations controlled Canada thistle better than high concentrations. High glyphosate concentration (108 μg/μl), high MON 0818 concentration (54 μg/μl), and large droplet size (2 μl) reduced 14C-glyphosate absorption and translocation compared with low glyphosate concentration (9 μg/μl), low MON 0818 concentration (4.5 μg/μl), and small droplet size (0.2 μl). High glyphosate and high MON 0818 concentrations may cause rapid tissue toxicity resulting in reduced translocation and poor perennial weed control.

The methyl ester of thiameturon {3-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] amino] sulfonyl]-2-thiophencarboxylic acid} toxicity to kochia [Kochia scoparia (L.) Schrad. # KCHSC] increased with surfactant concentration in the spray to 0.25% (v/v). High soil nitrogen fertility (165 ppm) enhanced kochia susceptibility to thiameturon compared to low nitrogen fertility (65 ppm). Nitrogen plus surfactant in the spray only partially overcame the effect of low soil nitrogen but did enhance thiameturon toxicity to kochia at all fertilities. Petroleum oil plus surfactant enhanced thiameturon so that kochia fresh weight reduction was similar regardless of soil fertility. Thiameturon toxicity to kochia generally increased with an increase in temperature regardless of relative humidity (RH) or adjuvants. An RH of 90 to 95% enhanced thiameturon toxicity to kochia regardless of temperature or adjuvants, except for petroleum oil plus surfactant with the low (10:8 C day:night) temperature regime. A simulated rain of 2 mm within 24 h after treatment reduced thiameturon toxicity to kochia. Drought stress (≤25% of field capacity) after thiameturon application reduced toxicity regardless of spray additives. The results of the various experiments indicated that thiameturon phytotoxicity would be greatest to kochia growing with high temperature and high RH, adequate soil moisture and nitrogen fertility, and when applied with petroleum oil plus surfactant.

The basis for differential susceptibility of tolerant rice (Oryza sativa L.), susceptible wild rice (Zizania palustris L.), and susceptible giant burreed (Sparganium eurycarpum Engelm. # SPGEU) to foliar application of 1.1 kg ai/ha of bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] was investigated by evaluating herbicide absorption, translocation, and metabolism. Giant burreed and wild rice absorbed more bentazon than rice at similar growth stages. Less than 10% of the absorbed bentazon was translocated out of the treated leaf of any of the species. Differential tolerance of bentazon among the three species was due to differences in the rate of bentazon metabolism. Rice metabolized 98% of the bentazon retained in the treated leaf 1 day after treatment (DAT), while giant burreed and wild rice metabolized less than 2% of the bentazon retained in the treated leaf 5 DAT.

Green foxtail [Setaria viridis (L.) Beauv. # SETVI] and proso millet [Panicum miliaceum (L.) #PANMI] growing under high water stress for 3 days before + 3 days after foliar applications of the methyl ester of haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} developed less herbicide injury than plants growing under low water stress. There was a 32% reduction in the retention of haloxyfop sprays by proso millet when growing under high water stress than when growing under low water stress. Haloxyfop spray retention by green foxtail was not affected by the degree of water stress. The translocation of 14C out of 14C-haloxyfop-treated leaves was significantly greater in plants of both species when growing under low water stress than when growing under high water stress. The conversion of 98% of the absorbed 14C-haloxyfop-methyl to 14C-haloxyfop and unidentified polar metabolites occurred in both species within 12 h of application. The green foxtail growing under low water stress contained greater concentrations of 14C-haloxyfop than did plants growing under high water stress. Levels of 14C-haloxyfop were the same in proso millet growing under high and low water stress. The reduced injury of green foxtail and proso millet growing under high water stress from postemergence sprays of haloxyfop can be attributed to a reduction in herbicide translocation in both species, plus a reduction in spray retention by proso millet or changes in the metabolism of the herbicide in green foxtail, which results in a reduction in the concentration of haloxyfop.

Imazaquin {2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-quinolinecarboxylic acid} absorption, translocation, and toxicity were investigated in yellow nutsedge (Cyperus esculentus L. # CYPES) and purple nutsedge (C. rotundus L. # CYPRO) after foliar treatment. Imazaquin rates from 0.125 to 0.375 kg ai/ha were sprayed on nutsedge plants at the four-leaf stage. Compared to untreated plants, these rates reduced the main shoot growth of yellow nutsedge by 70 to 86% and that of purple nutsedge by 80 to 92% at 28 days after application (DAA). However, the regrowth as measured by tiller production was significantly greater at 0.125 and 0.188 kg/ha rates than at higher rates. The plants treated with 0.313 and 0.375 rates had no rhizomes or tubers at the 28 DAA sampling. In yellow nutsedge, absorption of 14C-imazaquin increased from 36% at 1 DAA to 57% at 8 DAA. of the total absorbed 14C, 12% translocated from the treated area by 8 DAA. Roots and rhizomes accumulated equal amounts of radioactivity. In purple nutsedge, the absorption of imazaquin increased from 17% at 1 DAA to 53% at 8 DAA. Translocation of absorbed 14C in purple nutsedge at 8 DAA was 21%. Rhizomes accumulated significantly greater amounts of 14C than the roots.

Cotton (Gossypium hirsutum L. ‘Coker 315’), spurred anoda [Anoda cristata (L.) Schlecht. # ANVCR], and velvetleaf (Abutilon theophrasti Medik. # ABUTH) were grown in controlled-environment chambers at 29/23 C day/night temperature and 1000 μE·m–2·s–1 photosynthetic photon flux density (PPFD). Groups of plants were subjected to water stress by withholding water for 8 days, beginning at 27 days after planting. Cotton reached a lower leaf water potential than spurred anoda and velvetleaf following 8 days of withholding water. Following the drought, plants were rewatered for a 6-day recovery period. Water stress reduced plant height, leaf number, leaf area, total dry weight, stomatal conductance, transpiration, net assimilation rate, and leaf area duration in all species, in comparison with well-watered controls. Water stress decreased partitioning of plant biomass into leaves and increased partitioning into roots. Following rewatering, stomatal conductance and transpiration rates of previously stressed plants recovered to control levels within 28 h. Net assimilation rates of previously stressed spurred anoda also recovered to control levels. After 6 days of recovery, total dry weights and leaf areas of previously stressed plants of all three species remained below those of control plants. The overall effect of the drought and water stress was to delay the time at which spurred anoda and velvetleaf equaled or surpassed cotton in dry weight and leaf area, suggesting that drought early in the growing season under field conditions might increase the competitiveness of cotton relative to the two weeds.

Palmer amaranth (Amaranthus palmeri S. Wats. # AMAPA) residue was incorporated into soil to determine its allelopathic effects on the seedling growth of grain sorghum (Sorghum bicolor L. Moench.), cabbage (Brassica oleracea, var. capitata L.), carrot (Daucus carota L.), and onion (Allium cepa L.). Root and shoot growths were equally sensitive to the toxic effects of soil-incorporated Palmer amaranth. Growth of ‘Grand Slam’ cultivar of cabbage was 17 to 30% more sensitive than the growth of 'Sanibel’ cabbage. Growth of onion and carrot seedlings was less inhibited than either cabbage or grain sorghum. Growth of grain sorghum root was severely inhibited by 8000 and 16 000 ppm of Palmer amaranth in soil and was not affected by oven dryings other than lyophilization. Seedling growth was more severely inhibited by thyrsus and leaf tissues than by stem and root tissues of Palmer amaranth.

Greenhouse and growth chamber studies were conducted to determine conditions for infection of the fungal pathogen Colletotrichum truncatum (Schw.) Andrus and Moore on Florida beggarweed (Desmodium tortuosum (Sw.) DC. # DEDTO and to determine the host specificity of this fungus. Optimum conditions for disease development were 14 to 16 h incubation in 100% relative humidity (RH) at 24 to 29 C. Control of Florida beggarweed with 105 to 107C. truncatum spores/ml was greatest in the cotyledon stage and decreased with plant age. Ten of 18 Desmodium species tested were susceptible to the Florida beggarweed isolate of C. truncatum but 13 other plant species and varieties were resistant and 61 were immune.

Effects of propanil [N-(3,4-dichlorophenyl)propanamide] applied to three- to four-leaf rice (Oryza sativa L.) 1 or 7 days before, after, or tank mixed with methyl parathion (O,O-dimethyl-O-4-nitrophenyl phosphorothioate) were determined under different environmental conditions. Field experiments determined the effect on yield of drill-seeded rice, ‘Labelle’ for two planting dates in 1982 and ‘Lemont’ for one planting date in 1986. Treatments were applied at sunrise and at noon. Growth chamber and greenhouse experiments determined the effects of temperature, relative humidity (RH), and soil moisture on response of Labelle rice. In all experiments, propanil, both alone and with methyl parathion, resulted in 20 to 30% leaf burn during the first week after treatment with rapid recovery to less than 10% injury after 3 to 4 weeks. In field experiments, yields were not reduced in the treated rice below that in the untreated controls. In controlled-environment experiments, rice was not injured by propanil plus methyl parathion more than by propanil alone after 2 to 4 weeks. Both treated and untreated rice were injured more by the environmental conditions of high (40 C) temperature, low (40%) RH, and low (near the wilting point) soil moisture than by low (30 C) temperature, high (100%) RH, and flooded soil.

Consecutive annual applications of alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide] and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] were made to continuous no-till corn (Zea mays L. ‘Pioneer 3184’ in 1982 and 1983, ‘Pioneer 3744’ in 1984, and ‘Pioneer 3378’ in 1985 to 1987). In a 5-yr study, control of the dominant annual grass species, large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSA], by alachlor declined to less than 50% by the fifth year. Control of large crabgrass by metolachlor remained greater than 80% throughout the study but metolachlor allowed the establishment of a greater fall panicum (Panicum dichotomiflorum Michx. # PANDI) population in this and an additional 3-yr study than in chloroacetamide-free checks. In the 3-yr study in which giant foxtail (Setaria faberi Herrm. # SETFA) was dominant, annual applications of metolachlor and a microencapsulated formulation of alachlor provided better control in the second year than the emulsifiable concentrate formulation of alachlor, but formulation differences diminished in the third year.

Field experiments were conducted during 1985 and 1986 to determine the response of soybean [Glycine max (L.) Merr. ‘Coker 156’], pitted morningglory (Ipomoea lacunosa L. # IPOLA), and ivyleaf morningglory [Ipomoea hederacea (L.) Jacq. # IPOHE] to acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid}, fomesafen {5-[2-chloro-4-(trifluoromethyl) phenoxy]-N-(methylsulfonyl)-2-nitrobenzamide}, and lactofen {(±)-2-ethoxy-1-methyl-2-oxoethyl-5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-dinitrobenzoate}. Acifluorfen and lactofen were more phytotoxic to soybean 15 days after treatment (DAT) than fomesafen. All herbicides at low rates controlled 80% or more pitted morningglory. However, only the high rates (0.6 kg ai/ha) of acifluorfen and fomesafen controlled 80% or more ivyleaf morningglory 90 DAT. Full-season competition from untreated pitted morningglory reduced soybean seed yields 44 and 22% in 1985 and 1986, respectively, compared to 58 and 49% with untreated ivyleaf morningglory. Soybean seed yields were higher in plots receiving acifluorfen or fomesafen applications than lactofen applications.

Several herbicides were evaluated for control of white locoweed (Oxytropis sericea Nutt. T & G # OXRMA) and changes in botanical composition on two sites on high-elevation rangeland. White locoweed was more abundant and its population more stable on the rocky subalpine wind-swept ridge site than on the subalpine loam site. Picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid) at 0.6 and 1.1 kg ae/ha, and 2,4-D [(2,4-dichlorophenoxy)acetic acid] at 2.2 and 4.5 kg ae/ha eliminated white locoweed on the subalpine loam site, although the population on this site declined naturally. Clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) was the most effective herbicide on the subalpine wind-swept site. Clopyralid at 0.3 and 0.6 kg ae/ha, dicamba (3,6-dichloro-2-methoxybenzoic acid) at 2.2 kg ae/ha, and 2,4-D at 1.1 kg ae/ha plus clopyralid or picloram at 0.3 kg/ha killed all white locoweed plants. Lower rates of clopyralid (0.1 kg/ha), dicamba (0.6 and 1.1 kg/ha), 2,4-D (2.2 and 4.5 kg/ha), and triclopyr {[(3,5,6-trichloro-2~pyridinyl)oxy] acetic aicid)} (0.6, 1.1, and 2.2 kg ae/ha) killed 45 to 84% of white locoweed plants. Grass cover increased on most treated areas where white locoweed, forbs, and sagebrush declined. Cattle consumption of white locoweed declined following application of 2,4-D.

A single application of 0.56 or 0.84 kg ai/ha tridiphane [2-(3,5-dichlorophenyl)-2-(2,2,2-trichloroethyl) oxirane] plus 2.3 kg ai/ha of atrazine [6-chloro-N-ethyl-N′-(1-niethylethyl)-1,3,5-triazine-2,4-diamine] at the one-to three-leaf stage controlled large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSA] and fall panicum (Panicum dichotomiflorum Michx. #PANDI) 96% or more. A sequential application of 1.1 kg/ha of atrazine, in addition to the above single application, was required for control of the two grass species at the four-to six-leaf stage. Application of tridiphane plus atrazine to large crabgrass and fall panicum beyond the six-leaf stage was ineffective. Tridiphane at 0.75 kg/ha, applied alone, reduced the shoot dry weight of large crabgrass by 71%. The response of tridiphane and atrazine combinations at the four- to five-leaf stage of large crabgrass was additive.

In greenhouse and field studies, fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy] propanoic acid} controlled quackgrass [Agropyron repens (Beauv.) # AGRRE] in potato (Solanum tuberosum L. ‘Russet Burbank’). Quackgrass control with fluazifop at 0.25 and 0.5 kg ai/ha in the greenhouse was greatest with application at the two-leaf stage compared with the four-and six-leaf stages. Control was not affected by rhizome length, with similar control obtained of plants grown from 2- and 10-node rhizome pieces. Removal of quackgrass shoots at 6 or 24 h after treatment resulted in decreased control at application rates of 0.25 and 0.5 kg/ha. Fluazifop at 0.5 kg/ha controlled quackgrass treated at the four-leaf stage. The active enantiomer of fluazifop at half the rate of the racemic mixture controlled the quackgrass to the same extent. Fluazifop did not affect potato yield.

Experiments were conducted to determine the influence of various factors on asulam {methyl[(4-aminophenyl)sulfonyl] carbamate} toxicity to flax (Linum usitatissimum L.) and wild oats (Avena fatua L. # AVEFA). Asulam toxicity to both flax and wild oats generally increased as temperature, humidity, and soil moisture increased after treatment. Octoxynol {α-[p-1,1,3,3-tetramethyl butyl phenyl]-ω-hydroxypoly(oxyethylene)} in the spray solution increased asulam toxicity to both species in all environments. Octoxynol and trimethylenonypolyethoxyethanol (WK) enhanced asulam toxicity more than other adjuvants evaluated. Asulam toxicity to both flax and wild oats increased as octoxynol concentration in the spray increased. Flax tolerance to asulam generally increased with flax height at treatment. ‘Flor’ flax was the most asulam susceptible of six cultivars evaluated. A 2-mm simulated rainfall within 3 or 6 h after asulam treatment reduced toxicity to wild oats and flax, respectively.