We compared eight weed control systems in soybeans [Glycine max (L.) Merr.] using several combinations of the herbicides trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine), alachlor [2-chloro-2′,6′-diethyl-N-methoxymethyl)acetanilide], dinoseb (2-sec-butyl-,4, 6-dinitrophenol), chloroxuron [3-[p-(p-chlorophenoxy)phenyl]-1,1- dimethylurea], and linuron [3-(3,4-dichlorophenyl)-1- methoxy-1-methylurea] with or without cultivation to cultivation only and cultivation plus handhoeing. Cultivation plus handhoeing controlled the most weeds. Eight weed control systems using herbicides or herbicides plus cultivation controlled more weeds in soybeans than the system using only three cultivations. There was no significant difference in soybean yield between the system using three cultivations and six other systems using herbicides or herbicides plus cultivation. Trifluralin or alachlor applied as a preemergence treatment followed by postemergence treatments of chloroxuron, dinoseb, and linuron controlled weeds nearly as well as cultivation plus handhoeing. When dinoseb was applied repeatedly to leaves early after emergence, it severely injured soybeans, reduced soybean yield, and did not control sicklepod (Cassia obtusifolia L.). Sicklepod was the dominant weed species remaining at harvest.

A higher population of common purslane (Portulaca oleracea L.) developed on a smooth seedbed than a rough seedbed. Purslane germinated best when the seed were placed on the soil surface, and the percentage germination decreased progressively as depth of seed placement increased. Growth of common purslane was greater at elevated nutrient levels and was dependent on adequate phosphorus in the nutrient media. High soil temperature requirements for optimum germination make common purslane a middle to late-growing season weed in the central United States. Often preemergence herbicides which are effective on common purslane have become ineffective by the time the common purslane population has developed, and postemergence herbicides which do not injure the individual crop species must be relied on for common purslane control.

Plants produced by yellow nutsedge (Cyperus esculentus L. # CYPES) tubers planted in a field at the U.S. Cotton Research Station, Shafter, CA, at monthly intervals were harvested 2, 4, or 8 weeks after planting or at the end of a full season that varied from 12 to 37 weeks. In the 2 yr of the study, 1982 and 1983, tubers were slow to sprout in March and April, taking up to 8 weeks. From June through October about 60% of the plants emerged within 2 weeks of the planting date. Parent plants produced daughter plants by the 4-week harvest except for March, April, and October 1982, and March 1983 planting periods. All planting periods had daughter plants by the 8-week harvest. In 1982, plants of the June full-season planting had significantly more daughter plants than plants of other full-season treatments even though the June full season was 12 weeks shorter than the March full season. In 1983, the number of daughter plants produced by plants for the full-season harvest was equal for all monthly plantings regardless of the length of the full season. In 1982, for the May through September plantings, more tubers were produced by plants at the 8-week harvest than the number of tubers originally planted. In 1983, only plants of the June and August plantings produced more tubers by the 8-week harvest than had been planted. In both years, plants that grew for a full season produced more tubers than the number planted, up to 200-fold more.

Ethofumesate [(±)-2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate] was applied to dry soils (2%, w/w moisture content) that were either wetted immediately or remained dry for 1 to 8 days prior to wetting. Two degradation products were isolated with thin-layer and column chromatography from soils that were kept dry for 4 days before wetting. The major product was identified as 2,3-dihydro-3,3-dimethyl-2-oxo-5-benzofuranyl methanesulfonate which accounted for more than 80% of the degradation products. The products were detected 1 day after application to dry soil (between 1 and 3% moisture content), while at moisture contents greater than 3% (w/w) very little ethofumesate was degraded. Radiolabeled ethofumesate and breakdown products were extracted with methanol from dry and wetted soils, and the soil samples were oxidized to quantify nonextractable radioactivity. The percentage of nonextracted ethofumesate was at least 5% greater in dry soil than in wet soil. Activity loss of ethofumesate applied to dry soil probably is due to both chemical degradation and strong adsorption.

Imazamethabenz, an acetohydroxyacid synthase (AHAS)-inhibiting herbicide, was applied at a sublethal rate (200 g ai ha–1) to foliage of greenhouse-grown wild oat plants at the 2-leaf stage without tillers. Main shoot tissues were sampled 1 to 2 wk after imazamethabenz treatment and prepared for light microscopic examination. Histological observations showed that imazamethabenz treatment did not produce drastic changes on leaf structures but did affect chloroplast integrity of fully expanded 2nd leaf and inhibited differentiation of the young 3rd leaf 1 wk after application. The internode length and the number of cells in internodes of the herbicide-treated main stem were greatly reduced, presumably due to the inhibition by imazamethabenz of intercalary meristem cell division in early stages of internode elongation. One week after imazamethabenz application, histochemical studies revealed an increased accumulation of starch granules in chloroplasts of the 2nd leaf but reduced starch levels in the main stem. This confirmed the hypothesis that AHAS inhibitors affected phloem transport of photosynthates.

Based on an herbarium survey, clover broomrape (Orobanche minor J. E. Smith) was found to have an 116 yr history in the United States. It has been collected 98 times in a total of 32 counties in 12 states and the District of Columbia, and it appears to have become established in seaports and along railroads. It most commonly parasitizes red and white clover, but also burley tobacco, carrots, and several species of ornamental shrubs and herbs. Distribution of clover broomrape indicates either a pattern of repeated introductions from foreign sources, or a persistence in areas where the parasite has become established. While not presently a significant threat, the potential for damage to crops of economic importance cannot be ruled out. The flowers are autogamous.

Infection of Hydrilla verticillata by Macrophomina phaseolina was investigated using scanning and transmission electron microscopy. Sprigs of plants in petri plates were inoculated with suspensions of fungal hyphae. Samples of inoculated and noninoculated plants were taken over time. Fungal cells attached to lower epidermal cell walls but not the upper epidermal cell walls of leaves. In less than 40 h, penetration through the cell wall was completed and colonization of host cells was observed. Penetration of upper epidermis was limited to the cell wall adjacent to a lower epidermal cell. No penetration was observed through the outer cell wall of upper epidermis. Inhibition of penetration through the outer cell wall of the upper epidermis may be attributable to an osmiophilic layer below the cell wall. Disruption of the host cell walls and subsequent host cell death was preceded by massive colonization of the host by this pathogen.

The objectives were to compare the growth of black and eastern black nightshade and develop predictive models for their growth. Black and eastern black nightshade were planted on June 3 and 23, and July 12 in 1988 and May 28, June 17, and July 10 in 1989. Exponential models were strongly correlated with the growth of both species across all planting dates. Eastern black nightshade produced more biomass than black nightshade, although weight of berries was equivalent. Leaf area per plant 60 d after planting was five times greater for eastern black nightshade than black nightshade. Eastern black nightshade responded to self-shading by increasing specific leaf area.

In a 3-yr field study, seven dinitroaniline herbicides controlled all weeds adequately, except for two species. None of them controlled shepherdspurse [Capsella bursa-pastoris (L.) Medic.], and only nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline] controlled common ragweed (Ambrosia artemisiifolia L.). EPTC (S-ethyl dipropylthiocarbamate) was included as a standard of comparison and provided satisfactory control of all weed species. Three-year averages of alfalfa (Medicago sativa L.) injury ratings at herbicide rates estimated to be equivalent in biological activity to 0.8 kg/ha and 1.7 kg/ha trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) respectively were: butralin [4-(1,1-dimethylethyl)-N-(1-methylpropyl)-2,6-dinitrobenzenamine] 0% and 3%, benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine) 2% and 9%, profluralin [N-(cyclopropylmethyl)-α,α,α-trifluoro-2,6-dinitro-N-propyl-p-toluidine] 5% and 19%, AC92390 (N-sec-butyl-2,6-dinitro-3,4-xylidine) 6% and 17%, trifluralin 6% and 26%, fluchloralin [N-(2-chloroethyl)-2,6-dinitro-N-propyl-4-(trifluoromethyl)aniline] 14% and 45%, and nitralin 18% and 49%. EPTC caused an average 4% injury at 3.4 kg/ha. At equivalent rates to 0.8 kg/ha trifluralin, most treatments caused an increase in first cutting alfalfa yields accompanied by a decrease in weed yields, except in 1974 when few treatments resulted in increased alfalfa yields. Alfalfa recovered from early season injury caused by higher rates of the herbicides, so that total alfalfa yields were usually not reduced compared to the control. Total herbage yields (alfalfa + weeds) were not increased by any treatment, and were sometimes decreased, especially by high rates of the herbicides.

Theory and models of crop yield loss from weed competition have led to decision models to help growers choose cost-effective weed management. These models are available for multiple-species weed communities in a single season of several crops. Growers also rely on crop rotation for weed control, yet theory and models of weed population dynamics have not led to similar tools for planning of crop rotations for cost-effective weed management. Obstacles have been the complexity of modeling the dynamics of multiple populations of weed species compared to a single species and lack of data. We developed a method to use limited, readily observed data to simulate population dynamics and crop yield loss of multiple-species weed communities in response to crop rotation, tillage system, and specific weed management tactics. Our method is based on the general theory of density dependence of plant productivity and extensive use of rectangular hyperbolic equations for describing crop yield loss as a function of weed density. Only two density-independent parameters are required for each species to represent differences in seed bank mortality, emergence, and maximum seed production. One equation is used to model crop yield loss and density-dependent weed seed production as a function of crop and weed density, relative time of weed and crop emergence, and differences among species in competitive ability. The model has been parameterized for six crops and 15 weeds, and limited evaluation indicates predictions are accurate enough to highlight potential weed problems and solutions when comparing alternative crop rotations for a field. The model has been incorporated into a decision support tool for whole-farm management so growers in the Central Great Plains of the United States can compare alternative crop rotations and how their choice influences farm income, herbicide use, and control of weeds in their fields.

Renovation of common bermudagrass [Cynodon dactylon (L.) Pers.] turf to either ‘Tifway’ or ‘Tifdwarf’ bermudagrasses, zoysia (Zoysia japonica Steud. x Zoysia tenuifolia Willd. ex Trin. ‘Emerald’) or centipedegrass [Eremochloa ophiuroides (Munro) Hack.] was undertaken with the aid of herbicides. Glyphosate [N-(phosphonomethyl)glycine] applied to common bermudagrass turf followed by treatments of MSMA (Monosodium methanearsonate) + 2,4-D[2,4-dichlorophenoxy)acetic acid] alone or in sequence with DCPA (dimethyl tetrachloroterephthalate) reduced the cover of common bermudagrass in renovated Tifway or Tifdwarf bermudagrass turf. Dalapon (2,2-dichloropropionic acid) applied alone or in sequence with DCPA, MSMA + 2,4-D, or DCPA + MSMA + 2,4-D also reduced coyer of common bermudagrass in some plantings. Paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) and cacodylic acid (hydroxydimethylarsine oxide) did not reduce the cover of common bermudagrass in turf renovations. Slower growing Emerald zoysia and centipedegrass could not compete with the common bermudagrass that escaped the herbicide applications and renovation was unsuccessful.

In three field experiments at the University of Arkansas Rice Branch Experiment Station, Stuttgart, S-ethyl hexahydro-1H-azepine-1-carbothioate [molinate] at 2, 3, 4, and 6 lb/A was applied into the flood water 3, 6, 11, and 17 days after emergence of rice [Oryza sativa L.] and barnyardgrass [Echinochloa crusgalli (L.) Beauv.]. Molinate at 2 or 3 lb/A applied 3, 6, 11, or 17 days after emergence of rice and barnyardgrass, when weeds ranged from the one-leaf to tillering stages, provided acceptable weed control and rice tolerated these treatments satisfactorily. A rate of 3 lb/A frequently controlled barnyardgrass better than 2 lb/A, and usually was as effective as 4 or 6 lb/A. Sometimes, rates of 4 or 6 lb/A, applied 11 or 17 days after rice emergence, injured the crop moderately to severely and reduced grain yields.

August and October applications of glyphosate [N-(phosphonomethyl)glycine] and paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) were compared at two rates for pasture renovation. During the 2 yr of the experiment, sod suppression was frequently greater with October applications than with August applications. Medium red clover (Trifolium pratense L.) became established in all the plots, and density and yield tended to increase as grass suppression increased.

Glyphosate was compared over a 3-yr period with an ester of 2,4-D [(2,4-dichlorophenoxy)acetic acid] and picloram (4-amino-3,5,6-trichloropicolinic acid) for control of tall ironweed (Vernonia altissima Nutt.) when applied in August. Picloram killed from about 80 to 100% of the tall ironweed plants and was superior to 2,4-D. Glyphosate was inconsistent for controlling tall ironweed but could be used for killing perennial weeds as well as sod suppression.

Experiments were conducted in controlled environmental chambers to determine the influence of temperature on the phytotoxicity of seven soil-applied herbicides. Diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid} soil incorporated or surface applied, was more toxic to wild oat (Avena fatua L.) shoots at 10 and 17 C than at 24 C. Efficacy of diclofop was enhanced with soil incorporation. Diclofop toxicity to wild oat roots was not influenced by a change in temperature. EPTC (S-ethyl dipropylthiocarbamate) stimulated sugarbeet (Beta vulgaris L. ‘American Crystal Hybrid B’) shoot dry weight production at 10 C and caused dry weight reduction at 24 C. Atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] toxicity to barley (Hordeum vulgare L. ‘Larker’) and alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] toxicity to oats (Avena sativa L. ‘Chief’) increased with increased temperature from 10 to 17 C. Temperatures within the range of 10 to 24 C did not affect trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) toxicity to barley or BAY-5653 [N-(2-benzothiazolyl)-N-methylurea] or chloamben (3-amino-2,5-dichlorobenzoic acid) toxicity to oats.

Eastern black nightshade is a problem weed in soybeans primarily due to interference with harvesting operations and reductions in crop quality. Field and greenhouse studies were conducted in 1990 and 1991 at Harrow, Ontario, to determine whether sublethal rates of imazethapyr and metolachlor could suppress growth and berry production by eastern black nightshade. In the greenhouse, plants treated with metolachlor PRE at 0.8 kg ai ha−1 or imazethapyr POST at 30 g ai ha−1 (1/3 to 1/2 the labelled rates) produced significantly fewer berries in the first flower cluster, with fewer seeds per berry, than untreated plants. When a surfactant was added to the imazethapyr, almost all flower buds in the first cluster were aborted. Treated plants recovered from the damage, however, and did not differ significantly from control plants in dry weight or berry production 110 DAP. In the field, application of 50 g ai ha−1 imazethapyr POST (2/3 of the lowest labelled rate), with or without a surfactant, resulted in delayed flowering, abortion of most of the flower buds in the first cluster, and greatly reduced growth and total berry production between soybean leaf abscision and harvest. Application of metolachlor + metribuzin PPI in the field at 2/3 of the labelled rate (1.6 + 0.25 kg ai ha−1) was not sufficient to reduce nightshade growth and berry production after soybean leaf abscision. Sublethal rates of imazethapyr and metolachlor did not reduce seed viability in either the greenhouse or the field.

Root absorption of subtoxic levels of metribuzin and its ethylthio analog (ethyl-metribuzin) by downy brome, jointed goatgrass, and winter wheat increased by a factor of three to five times as temperature increased from 10 to 20 C. Absorption of ethyl-metribuzin per gram dry weight was similar for all three species. Absorption and distribution of ethyl-metribuzin, but not metribuzin, were similar per gram dry weight in downy brome and jointed goatgrass. Absorption of metribuzin per gram dry weight was lower for winter wheat than for the other two species at 20 C. In general, the ratio of absorbed ethyl-metribuzin detected in shoots to that in roots was less in winter wheat and jointed goatgrass than in downy brome. The absorption by roots of 14C-herbicides relative to water was similar for winter wheat and jointed goatgrass. Absorption of both 14C-herbicides by winter wheat and jointed goatgrass was nonpreferential with respect to water absorption at 10 and 15 C. However, at 20 C 14C-herbicide absorption was reduced 5 to 30% with respect to water absorption. Downy brome absorption of 14C-herbicides with respect to water was 30 to 50% less than that of the other two species.

The effect of the bleaching and non-bleaching phenylpyridazinones, norflurazon [4-chloro-5-(methylamino)-2-(α,α,α-trifluoro-m-tolyl)-3(2H)-pyridazinone] and BAS 29095 [4,5-dimethoxy-2-phenyl-3(2H)-pyridazinone], on chlorophyll fluorescence of the green alga, Scenedesmus acutus, was investigated and compared to other bleaching herbicides, difunon3 [EMD-IT 5914, 5(dimethylamino-methylene)-2-oxo-4-phenyl-2,5-dihydrofuranecarbonitrile-(3)] and the diphenyl ether, oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene]. Following chlorophyll fluorescence during short-term cultivation in the presence of herbicides and comparing it to physiological parameters such as chlorophyll content and packed cell volume allowed for rapid screening to detect different primary herbicidal modes of action. Two primary bleaching effects caused by either inhibition of carotene biosynthesis (certain substituted pyridazinones and difunon) or peroxidative degradation of membrane lipids (certain diphenyl ethers) led to completely different fluorescence signals. Growth of algae in the presence of a carotene biosynthesis inhibitor resulted in a rapid rise to maximum fluorescence, followed by a single decay phase, whereas bleaching diphenyl ethers led to a rapid loss of total fluorescence. Non-bleaching phenylpyridazinones, which act as weak electron transport inhibitors, inhibited variable fluorescence. Detoxication during algal growth became evident by recovery of the fluorescence induction.

Absorption and translocation of (2,4-dichlorophenoxy)-acetic acid (2,4-D) and 4-amino-3,5,6-trichloropicolinic acid (picloram) were measured in defoliated and intact field bindweed (Convolvulus arvensis L.) plants. Radioactivity was applied as 5 μl of triethylamine salts of 2,4-D and picloram with an activity of 0.15 μc to a middle leaf in intact and partially-defoliated plants. After treatment for 96 hr, 14C-activity in untreated leaves, stems, growing tips, and roots was measured. Removal of all leaves significantly reduced absorption but not translocation of both 2,4-D and picloram. A greater percentage of the applied picloram than 2,4-D was absorbed in all treatments. Translocation of 14C of both 2,4-D and picloram was greater when (a) upper and lower leaves were removed, (b) upper leaves only were removed, and (c) lower leaves only were removed than (d) when plants were intact. Removal of lower (older) leaves reduced translocation more than removal of upper (younger) leaves.

The growth of tomato (Lycopersicoti esculentum Mill., var. Heinz 1350) plants was enhanced by low concentrations of both N,N-dimethyl-2,2-diphenylacetamide (diphenamid) and the filtrate from two fungal species Trichoderma viride (Tode) Harz and Aspergillus candidus Link. High concentrations of the filtrate from these fungi inhibited the growth of tomatoes, but this was overcome by the addition of diphenamid. Diphenamid also increased the growth of these two fungi.

A wide margin of crop safety is a desirable trait of POST herbicides, and investigation of crop tolerance is a key step in evaluation of new herbicides. Six field experiments were conducted in Ontario, Canada, from 2017 to 2018 to examine the influence of corn (Zea mays L.) hybrid (DKC42-60RIB, DKC43-47RIB, P0094AM, and P9840AM), application rate (1X and 2X), and application timing (PRE, V1, V3, and V5) on the tolerance of field corn to tolpyralate, a new 4-hydroxyphenyl pyruvate dioxygenase inhibitor, co-applied with atrazine. Two corn hybrids (DKC42-60RIB and DKC43-47RIB) exhibited slightly greater visible injury from tolpyralate + atrazine, applied POST, than P0094AM and P9840AM at 1 to 2 wk after application (WAA); hybrids responded similarly with respect to height, grain moisture, and yield. Applications of tolpyralate + atrazine at a 2X rate (80 + 2,000 g ai ha−1) induced greater injury (≤31.6%) than the field rate (40 + 1,000 g ha−1) (≤11.6%); the 2X rate applied at V1 or V3 decreased corn height and slightly increased grain moisture at harvest. On average, field rates resulted in marginally higher grain yields than 2X rates. Based on mixed-model multiple stepwise regression analysis, the air temperature at application, time of day, temperature range in the 24 h before application, and precipitation following application were useful predictor variables in estimating crop injury with tolpyralate + atrazine; however, additional environmental variables also affected crop injury. These results demonstrate the margin of corn tolerance with tolpyralate + atrazine, which provides a basis for optimization of application timing, rate, and corn hybrid selection to mitigate the risk of crop injury with this herbicide tank mixture.