Interference of Powell amaranth (Amaranthus powellii S. Wats. ♯ AMAPO) in sugarbeet (Beta vulgaris L. ‘Mono Hy A4’) was determined in field experiments. Yield of sugarbeet roots and recoverable sucrose/ha decreased as the density of Powell amaranth increased. At densities of 6, 12, 18, and 24 Powell amaranth plants/30 m of row, root yields were reduced 8, 14, 24, and 25%, respectively, and recoverable sucrose yields were reduced 7, 13, 23, and 24%, respectively. The minimum number of Powell amaranth plants required per 30 m of row to reduce sugarbeet root yields was estimated to be nine in 1982 and 11 in 1983.

Atrazine is the most widely used herbicide in the U.S. and has been detected in surface water and groundwater. Technologies are needed for onsite and in situ remediation of water and soil containing atrazine. We investigated the potential of using fine-grained, zero-valent iron (Fe0) to remove atrazine and promote its degradation in contaminated water and soil. Atrazine loss from aqueous solution increased with increasing Fe0 concentration (w/v). Agitating 20 μg 14C-ring-labeled atrazine L−1 with 10% Fe0 (w/v) removed 92% of the 14C from solution within 48 h. Only about 4% of the 14C lost from solution was extractable from the iron with 3 mM CaCl2 (readily available pool), 81% was extractable with CH3CN (potentially available pool), and 11% was unextractable residues. A companion experiment indicated that most of the 14C extracted from the iron with 3 mM CaCl2 after the 48-h Fe0 treatment was unaltered atrazine, while the CH3CN extract contained approximately 33% atrazine and 48% was unidentified atrazine transformation products. Treating a highly contaminated solution (20 mg atrazine L−1) with 20% Fe0 (w/v) removed 88% of the 14C (added as 14C-ring-labeled atrazine) from solution within 48 h. Deethylatrazine was the main atrazine transformation product detected in solution after treatment, but small amounts of deisopropylatrazine, didealkylatrazine, and hydroxyatrazine were also found. Treating Sharpsburg surface soil containing 1 mg atrazine kg−1 with Fe0 (2%, w/w) increased atrazine mineralization from 4.1 to 11.2% after 120 d. Pyrite (4% FeS2, w/w) also increased atrazine mineralization in surface soil, but was less effective in the presence of NO3 − or SO4 2− (100 mg kg−1 soil). Adding 2% Fe0 (w/w) and 100 mg NO3 − kg−1 to contaminated subsurface soil increased atrazine mineralization from 0.4 to 8.2% within 120 d, and unextractable residues increased from 4.6 to 9.8%. These results indicate iron can sorb atrazine and promote its transformation in water and soil.

The fate of 14C-sethoxydim {2-[1-(ethoxyimino) butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} in an aqueous solution and on glass exposed to light was evaluated. Within 1 h, more than 80% of the 14C-sethoxydim was transformed to six major products. Qualitatively the transformations were similar for both systems, and a single end product constituted the majority of 14C after 72 h. Two transitory compounds were found to be phytotoxic to barnyardgrass [Echinochloa crus-galli (L.) Beauv. ♯ ECHCG] and were more stable than sethoxydim. A nonphytotoxic compound isolated and identified by mass spectroscopy was desethoxy-sethoxydim.

Simazine [2-chloro-4,6-bis(ethylamino)-s-triazine] inhibited photosynthesis 50% at concentrations of 1.1 μM for Spirogyra jurgensii (Kutz), 3.0 μM for Pithophora oedogonia (Mont.) Wittr., and 3.8 μM for Cladophora glomerata (L.) Kutz. Photosynthesis of Ankistrodesmus braunii (Brun.), a nonfilamentous species, was inhibited the same amount by 4.7 μM simazine. The filamentous algal species had significant reductions in growth but no other phytotoxic symptoms when exposed to 5 μM simazine at light intensities of 100 μE·m–2·s–1 and below. Algicidal effects did occur at a light intensity of 400 μE·m–2·s–1 and were most severe in Spirogyra. The relationship between light intensity and simazine toxicity indicates algicidal effectiveness on these filamentous algae will be limited in habitats where light is reduced by turbidity, depth, or self-shading.

Experiments were conducted in 1993 and 1994 to determine if seed treated with disulfoton at 3, 6, or 12 g ai kg−1 reduced bleaching of rice foliage caused by clomazone applied delayed preemergence at 0.56, 1.1, 1.7, or 2.2 kg ai ha−1 on silt loam and silty clay soils. Clomazone injured rice more on silt loam soil than on silty clay soil. Disulfoton reduced bleaching caused by clomazone. In additional field experiments conducted during 1995 and 1996, clomazone at rates as high as 2.2 kg ha−1 did not affect grain yield in seven of 10 experiments. Clomazone at rates below 1.7 kg ha−1 did not reduce grain yield in any of the experiments.

The aim of this study was to test whether herbicide resistance in rigid ryegrass has led to increased densities of this weed in Western Australian (WA) cropping fields. A total of 503 wheat fields with previously unknown management history and weed status were visited prior to harvest across 15 agronomic areas of the central WA cropping belt in 1998 and 2003. Rigid ryegrass density was visually assessed and, where possible, seed was collected from the population. Ryegrass was found in 91% of the wheat crops sampled. Ryegrass populations were tested in the following year for resistance to chlorsulfuron, sulfometuron, diclofop, and clethodim. With the use of nonparametric and regression statistical methods, resistance status, including multiple-resistance status, was not found to be associated with higher weed density. The results show that growers are generally maintaining low densities in fields with herbicide-resistant rigid ryegrass. The most common rigid ryegrass density at harvest time was less than 1 plant m−2 in both resistant and susceptible populations. Field and model-based studies of weed and herbicide resistance management that allow populations to continue at very high densities are unlikely to reflect common grower practice.

Synthetic rubbers, synthetic plastic polymers (polyvinyl chlorides [PVC]), polyurethane blends, and polyethylene blends make up modern-day agricultural spray hoses. The objective of this study was to determine whether agricultural hose types would differ with respect to 3,6-dichloro-2-methoxybenzoic acid (dicamba) sequestration. Field and greenhouse studies were conducted to evaluate the sequestration potential of dicamba within five agricultural hose types when cleaned with different cleanout procedures. Rinsate solutions were applied to soybean, which was used as a bio-indicator to test for cleanout efficiency. Differences among hose types and cleanout procedures exist with observations including soybean injury, height reduction, dry matter, yield, and part per million by volume (ppmv) analyte retained. The makeup of PVC polyurethane-blend and synthetic rubber–blend hoses increased retention of dicamba analyte when compared with the polyethylene blend hose. No differences were observed after the addition of ammonia to the cleanout solution when compared with water alone. Differences in a hose type’s ability to sequester the dicamba analyte may have more to do with the hose’s internal chemical composition, manufacturing process, and composition breakdown. Scanning electron microscopy revealed imperfections in new PVC polyurethane and synthetic rubber hoses that eventually lead to inner wall depletion of these hose types. This is in contrast to what was found in the polyethylene-blend hose type, in which the inner wall is smooth and free of imperfections.

Studies were conducted to determine the effect of soil moisture, seedling age, and exposure of plant parts on control of barnyardgrass [Echinochloa crus-galli (L.) Beauv.] with diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid}, formulated as the methyl ester. In a Warden silt loam, moisture content of 10% or more was needed for satisfactory diclofop control of slow-growing barnyardgrass under cool, early-season conditions. Soil moisture was less critical when temperatures were higher and barnyardgrass was growing rapidly. Roots and emerging shoots both absorbed diclofop from the soil, but both plant parts were inhibited more when diclofop was applied to the roots than to the shoots. Barnyardgrass was injured from diclofop applied postemergence to either roots or shoots separately, but phytotoxicity was greatest when the whole plant was exposed. When the soil was treated, control increased with increasing amounts of post-treatment overhead irrigation. Two-leaf and four-leaf barnyardgrass plants were equally susceptible to diclofop applied postemergence, but resistance increased with age in plants with more than four leaves.

Purple nutsedge (Cyperus rotundus L.) was grown under greenhouse conditions as single tubers and various tuber chain systems. Single and repeated applications of amine methylarsonate were made to shoots of single tubers and shoots of terminal tubers in chain arrangements, and visual toxicity symptoms were noted in shoot growth both from treated tubers and from other tubers in chain arrangements. Arsenic (As) was translocated (as indicated by As content) laterally to tubers separated by at least four tubers from the treated shoot. The tuber on the opposite end of the chain from the treated shoot tended to be higher in As content than the middle tubers, and translocated As tended to be higher in tubers from which active growth was present or developed. No apparent relationship was found between As content of tubers and their ability to produce new shoots. There was some tendency for tubers to produce more than one shoot in the initial regrowth following treatment. Tuber lethality following repeated treatments evidently was due to depletion of food reserves and/or bud supply from increased sprouting and not to the accumulation of a specific level of As in the tuber.

One of the most marked effects of herbicidal concentrations of 2,4-D (2,4-dichlorophenoxyacetic acid) is the swelling and proliferation of basal stem tissues. Sell et al. reported a large increase in the protein content of stems of bean plants treated with 2,4-D. Shaw, et al. observed an increase of total protein in plants treated with 2,4-D and Rebstock, et al. found the nucleic acid content to double in the stems of bean plants treated with 2,4-D. Rebstock et al. postulated that nucleic acid was involved in the unusual growth and development of the plant. Skoog has presented an attractive hypothesis linking auxin action with nucleic acid metabolism. Current biochemical investigations leave little doubt that RNA (ribonucleic acid), particularly of the microsome fraction of the cytoplasm, is involved in protein synthesis. Furthermore, RNA appears to be implicated in oxidative phosphorylation and ion absorption, two processes known to be affected by 2,4-D.

Greenhouse studies were conducted to evaluate absorption, translocation, and metabolism of 14C-glufosinate in glufosinate-resistant cotton, nontransgenic cotton, Palmer amaranth, and pitted morningglory. Cotton plants were treated at the four-leaf stage, whereas Palmer amaranth and pitted morningglory were treated at 7.5 and 10 cm, respectively. All plants were harvested at 1, 6, 24, 48, and 72 h after treatment (HAT). Absorption of 14C-glufosinate was greater than 85% 24 h after treatment in Palmer amaranth. Absorption was less than 30% at all harvest intervals for glufosinate-resistant cotton, nontransgenic cotton, and pitted morningglory. At 24 HAT, 49 and 12% of radioactivity was translocated to regions above and below the treated leaf, respectively, in Palmer amaranth. Metabolites of 14C-glufosinate were detected in all crop and weed species. Metabolism of 14C-glufosinate was 16% or lower in nontransgenic cotton and pitted morningglory; however, metabolism rates were greater than 70% in glufosinate-resistant cotton 72 HAT. Intermediate metabolism was observed for Palmer amaranth, with metabolites comprising 20 to 30% of detectable radioactivity between 6 and 72 HAT.

The failure of PRE and POST applications of atrazine to control Palmer amaranth in recent field studies prompted further investigation to determine whether this population had evolved resistance to multiple herbicide sites of action, including glyphosate (Group 9), thifensulfuron (Group 2), and atrazine (Group 5). Greenhouse and laboratory experiments were conducted to: (1) confirm the presence of resistance to glyphosate, an ALS inhibitor (thifensulfuron), and atrazine in a single Palmer amaranth population; and (2) establish the molecular basis for resistance to these herbicide sites of action. In the greenhouse, glyphosate+thifensulfuron+atrazine at 1.26 kg ae ha−1+0.0044 kg ai ha−1+1.12 kg ai ha−1 provided 55% control of the suspected multiply resistant (MR) Palmer amaranth population and 93% control of the known susceptible population (S). The decreased sensitivity of the MR population compared with the S population at labeled use rates of these herbicides indicated that this population was likely resistant to three different herbicide site of action groups. The RF values for POST applications of glyphosate, thifensulfuron, and atrazine were 12.2, 42.9, and 9.3 times, respectively, for the MR Palmer amaranth population relative to the S population. The RF value for atrazine PRE for the MR population was 112.2 times. Laboratory experiments confirmed that the mechanisms for resistance to ALS-inhibiting herbicides and glyphosate in the MR Palmer amaranth population were target-site based, via amino acid substitution and amplified EPSPS copy number, respectively. There was a Pro to Leu substitution at site 197 in the ALS inhibitor–resistant plants, and there was a greater than 50-fold increase in EPSPS copy number in the glyphosate-resistant plants. There were no nucleotide changes in the psbA gene; therefore, atrazine resistance in this population was not target-site mediated. The evolution of this multiple herbicide-resistant Palmer amaranth population poses significant management challenges to Michigan farmers.

Studies were conducted to determine the growth, fecundity, and competitive ability of an acetyl-CoA carboxylase (ACCase)–inhibitor resistant (R) sterile wild oat biotype compared with a susceptible (S) biotype. Seed germination studies indicated that there were no differences in seed germination and seedling vigor between R and S biotypes at any temperature regime. R and S biotypes were grown under noncompetitive and competitive arrangement in the greenhouse. Under noncompetitive greenhouse conditions, growth of the R biotype was similar to that of the S biotype on the basis of plant height, canopy area, and plant biomass. Seed production and weight of R and S plants were also at the same levels. Furthermore, relative competitiveness among the R and S sterile wild oat biotypes was investigated by means of replacement series experiments. The R and S biotypes were compared under seven mixture proportions (6 : 0, 5 : 1, 4 : 2, 3 : 3, 2 : 4, 1 : 5, and 0 : 6). No significant differences in competitive ability were observed between R and S biotypes on the basis of plant height, canopy area, or plant biomass. In most cases, relative crowding coefficient (RCC) values at 20, 60, and 100 d after transplanting (DAT) were close to one, indicating equal competitiveness between the R and S biotypes of wild oat used in this competitive study. However, in some cases, the RCC value was 1.31 for plant height, evident of a slight competitive advantage for the R biotype at 100 DAT. In general, ACCase-inhibitor R and S sterile wild oat biotypes were equally competitive, clearly without any growth penalty for R plants in either noncompetitive or competitive conditions.

Greenhouse and field studies were conducted to compare the phytotoxicity of HOE 23408 {methyl 2-[4-(2,4-dichlorophenoxy)phenoxy]-propanoate} to several crops and annual grass weeds, and to determine the herbicides's soil mobility and persistence. In general, the order of susceptibility of 13 seedling grassy weeds remained constant, whether the herbicide was applied preplant incorporated, pre-emergence, or postemergence. The herbicide was most phytotoxic when it was applied either preplant incorporated or early postemergence. Grain sorghum [Sorghum bicolor (L.) Moench ‘BR-54′] and oats (Avena sativa L. ‘Cimarron’) were moderately susceptible to HOE 23408, whereas barley (Hordeum vulgare L. ‘Will’) exhibited marginal tolerance. Wheat (Triticum aestivum L. ‘Triumph 64′) and cotton (Gossypium hirsutum L. ‘Westburn 70′) showed tolerance to HOE 23408 at rates up to 6 ppmw, and soybean [Glycine max (L.) Merr. ‘Bragg’] and peanut (Arachis hypogaea L. ‘Spanhoma’) demonstrated tolerance to concentrations as high as 24 ppmw. The soil mobility of HOE 23408 was similar to that of trifluralin (a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine). No soil phytotoxicity was found 8 weeks after herbicide application in the field or under laboratory incubation conditions of 5 or 10% soil moisture at 21 C. Dissipation was much slower at a temperature of 4.4 C, regardless of the soil moisture level.

Diffuse knapweed (Centaurea diffusa Lam.) and spotted knapweed (C. maculosa Lam.) presently infest approximately 1.5 million ha of pasture and rangeland in Washington, Montana, Idaho, Oregon, and California. The serious losses caused on lands where returns from herbicidal control are marginal or less prompted the testing and introduction of two strains of a seed-head fly (Urophora affinis Frlfld.) as a biological-control agent in these states. Over 27 000 flies were released in about equal numbers on both weeds during the years 1974 to 1977 and in 1979 and 1980. The fly became established in all states where it was released. The adult was found to disperse over 76 m from release point from 1974 to 1976, and to reduce the number of seeds per flower head in sampled heads by 80% in northern Washington and over 64% at the Heppner, Oregon site. A newly released moth (Metzneria paucipunctella Zell.) and a root-boring beetle (Spbenoptera jugoslavica Obenb.) are expected to cause additional pressure on these plants. The reproductive potential of the knapweeds is such that more natural enemies will be needed to provide enough stress to reduce these weedy species to an acceptable level.

Peanut (Arachis hypogaea L. ‘Florigiant’) seed yield was reduced 25% by a fall panicum (Panicum dichotomiflorum Michx.) density of one weed per 4.9 m of row. Greater weed densities resulted in greater yield losses. Peanut seed yield was reduced by fall panicum interference for 2 weeks or more after peanut emergence. Peanuts kept weed-free for 8 weeks after emergence failed to yield as well as those kept weed-free all season. However, control for the first 2 weeks appeared to be the most critical.

Over a 4-yr period, glyphosate [N-(phosphonomethyl)glycine] was applied over-the-top to soybeans [Glycine max (L.) Merr.] at five rates, from 0.56 to 3.36 kg/ha, at four periods of time prior to harvest, 23 to 29 days, 15 to 21 days, 7 to 12 days, and 1 to 4 days. Soybean yields were reduced when glyphosate was applied at 2.24 and 3.36 kg/ha 23 to 29 days before harvest. Soybean seed were discolored following all five rates of glyphosate applied 23 to 29 days before harvest, following glyphosate at 1.12 to 3.36 kg/ha applied 15 to 21 days before harvest, and following glyphosate at 3.36 kg/ha applied 7 to 12 days before harvest. Germination of soybean seed was reduced at 30 C only when glyphosate was applied at 2.24 and 3.36 kg/ha 23 to 29 days before harvest, or at 3.36 kg/ha applied 15 to 21 days before harvest. At alternating temperatures (10.6 C for 72 h followed by 30 C for 72 h), all treatments applied 23 to 29 days before harvest reduced soybean seed germination; glyphosate at 1.12, 1.68, and 3.36 kg/ha applied 15 to 21 days before harvest also reduced germination. Seed from plots treated with glyphosate 23 to 29 or 15 to 21 days before harvest produced atypical soybean plants. Glyphosate at 2.24 and 3.36 kg/ha applied 23 to 29 days before harvest reduced the oil content in soybean seed, but none of the treatments consistently affected the protein content.

Giant foxtail, woolly cupgrass, and wild-proso millet infest millions of hectares of land devoted to corn production in the midwestern U.S. Control of these species and effects on corn grain yield were evaluated at various timings using POST applications of nicosulfuron vs. applications of various PRE herbicides at 17 locations across the midwestern U.S. in 1992 and 1993. Nicosulfuron applied to 5 to 10 cm giant foxtail and woolly cupgrass provided greater control than that observed with selected PRE herbicides. Giant foxtail control with nicosulfuron averaged 88%, and control of woolly cupgrass averaged 77% across all sites. Nicosulfuron, applied to 5 to 10 cm wild-proso millet, provided a level of control similar to that of selected PRE herbicides. Corn grain yield was greater when giant foxtail was controlled POST with nicosulfuron vs. PRE control with selected soil-applied herbicides. Corn grain yields were similar when nicosulfuron was applied POST to 5 to 10 cm woolly cupgrass or wild-proso millet vs. PRE control of these grass weeds. Across a broad range of geographical locations, nicosulfuron, applied POST to 5 to 10 cm tall grass, provided greater or similar levels of weed control vs. the selected PRE herbicides, with no deleterious effect on grain yield.

Italian ryegrass [Lolium perenne L. spp. multiflorum (Lam.) Husnot] is a troublesome weedy species in many regions of California. Its control has been chiefly dependent on herbicides due to their effectiveness and practicality and, as result, herbicide-resistant populations have been selected. Poor control of a population of L. multiflorum with paraquat was recently reported in a prune orchard in Hamilton City, CA. A series of experiments were carried out to characterize the response of this population to several POST herbicides, study the mechanisms of resistance, and investigate alternative chemical management options in tree crops. A known susceptible (S) and the suspected resistant population (PRHC) were subjected to greenhouse dose–response experiments with clethodim, fluazifop-P-butyl, glufosinate, glyphosate, paraquat, pyroxsulam, rimsulfuron, and sethoxydim. A 310-bp fragment of the EPSPS gene containing position 106 was sequenced from PRHC and S. Field experiments were carried out in a prune orchard with PRE herbicides commonly used by perennial crop growers in California. Greenhouse dose–response experiments confirmed that PRHC is resistant to paraquat, as well as multiply resistant to clethodim and glyphosate. The EPSPS gene of PRHC is heterozygous for glyphosate resistance at position 106, where one allele exhibited proline substituted by serine and the other by alanine. Field experiments with PRE herbicides indicated that tank mixes containing indaziflam and flumioxazin can provide adequate L. multiflorum control up to 150 d after treatment. Poor weed management practices, such as overreliance on a single site of action, have frequently been associated with the selection of herbicide-resistant L. multiflorum populations around the world, and adequate herbicide-resistance management programs are necessary for growers to maintain economic sustainability even after evolution of herbicide-resistant weeds in their fields.

Giant foxtail (Setaria faberii Herrm.) germinated, emerged, and produced panicles containing viable seeds when sown during the greater part of the growing season. The height of the plant, size of panicle, and number of seeds produced depended on date of planting. Cutting to 2 inches at various stages of growth did not prevent further growth and reflowering but reduced the size of the panicle and the number of seeds. Mowing in May and June allowed giant foxtail to produce two crops of viable seeds.