Soil solarization is a process of soil disinfestation that involves solar heating of moist soil covered with transparent polyethylene film. This nonchemical approach to controlling soil-borne pests is being investigated as an alternative to methyl bromide fumigation. Summer solarization controlled annual weed species and suppressed purple nutsedge. Although some nutsedge tubers sprouted despite the solarization treatment, the resulting shoots were almost always trapped under the clear solarization film. Conversely, in rows that were mulched with black film, nutsedge rhizomes punctured the film so that leaf expansion occurred above the film. In controlled pot experiments conducted in darkness, yellow nutsedge rhizomes readily penetrated 19- and 30-μm clear films as effectively as opaque films. Thicker clear films and bubble film reduced nutsedge penetration. In the greenhouse and laboratory, nutsedge penetration of transparent polyethylene film was inversely related to irradiance levels when the film was in direct contact with the soil. However, when there was a 5- to 10-mm space between the soil and the film, the lowest irradiance level (30 μmol m−2 s−1) was as effective as 320 μmol m−2 s−1 in reducing penetration by purple nutsedge. The film penetration by nutsedge rhizomes appears to be linked to a light-dependent morphological change from rhizome growth to leaf development, which occurs before film penetration with clear mulch and after film penetration with opaque mulch. The alternate sprouting and foliar scorching of nutsedge shoots trapped under clear films could potentially be exploited to deplete nutsedge tubers that occur at soil depths that do not develop lethal temperatures under soil solarization.

Ridge truncation methods affected weed populations, weed control, and corn yields in a ridge-tillage production system. Ridges were left undisturbed, partially truncated, deeply truncated, or destroyed by full-width tillage. The effect of truncation on weed densities and control (visual estimates of biomass reduction) varied by weed species, herbicide treatment, and time of observation. Without herbicide, deep truncation resulted in the lowest densities of all species except giant foxtail. Band application of herbicide controlled all weed species as well as broadcast application following deep truncation. When herbicides were broadcast, weed control was usually not affected by ridge truncation. Ridge truncation often increased corn yields compared with no truncation due to better weed control. While deep truncation often resulted in lower weed populations following herbicide treatment than shallow truncation or disking, differences were not great enough to affect corn yields. When ridges were truncated, broadcast herbicide did not increase corn yields compared with banded herbicide.

A screening method was used to characterize seed thermal responses of prostrate knotweed and common purslane, two important weeds invading wheat in the humid Pampa. Through this method, it was possible to detect thermal conditions that induce or break dormancy in both species. In addition, we were able to quantify changes in dormancy level in seed populations as a function of time of burial after dispersal, through changes in width of the thermal range within which germination can occur. Plotting the overlap of this thermal range and observed soil temperature throughout the year allowed the prediction of the seedling emergence period. This prediction was in agreement with observed seedling emergence in the field for both species, during 2 consecutive yr. From the analysis carried out under laboratory conditions, it was also possible to estimate required thermal time for germination of the nondormant fraction of the population and the base temperature above which thermal time is accumulated. The results obtained from this study are the basis for the formulation of seed germination models that predict not only the occurrence of seedling emergence in the field, but also the dynamics of germination within those periods.

Field studies were conducted from 1995 to 1997 near Tifton, GA, to determine the benefits of stale seedbed weed control in cucumber. Three stale seedbed management systems—(1) power till stale seedbeds twice (2 ×), (2) glyphosate application immediately after planting, and (3) combination system of stale seedbeds power tilled once 2 wk prior to planting followed by glyphosate application immediately after planting cucumber—were evaluated as main plots. Subplots were weed management systems after planting cucumber: intensive, basic, and cultivation alone. Weed densities were generally greater in 1996 and 1997 than in 1995. Yellow nutsedge was the overall predominant species in 1995 (46 plants m−2), with Florida pusley being the predominant species in 1996 and 1997, at 80 and 124 plants m−2, respectively. Generally, stale seedbeds shallow tilled 2 × had fewer weeds and greater cucumber yields than stale seedbeds treated with glyphosate. Glyphosate did not adequately control emerged Florida pusley on stale seedbeds, resulting in reduced cucumber yield. Clomazone preemergence and bentazon/halosulfuron postemergence were used for broadleaf weed control in the intensive weed management system. These herbicides injured cucumber plants, delayed maturity, and reduced yield. Based on our results, stale seedbeds shallow tilled 2 × can be integrated into cucumber production and provide effective cultural weed control. Furthermore, these systems will replace the need for potentially injurious herbicides.

Field studies were conducted in Colorado and New Mexico to examine growth and development of spurred anoda accessions from Colorado, Mississippi, New Mexico, and North Carolina. Accessions were grown in a common garden in both locations. Leaf and stem weight ratios, leaf area ratio, and leaf area per plant were determined. North Carolina and Mississippi accessions were similar in morphology and appearance. Leaf shape, degree of pubescence, and coloration were different in the Colorado and New Mexico accessions. At both sites, the Colorado accession was taller and the canopy wider than other accessions. In Colorado in 1993, North Carolina and New Mexico accessions had the highest total weight followed by Colorado, then Mississippi. In 1994, final total weights of North Carolina, Mississippi, and New Mexico accessions were similar and greater than the Colorado accession. All accessions had similar final total weights in New Mexico in 1993. In 1994, Mississippi, North Carolina, and New Mexico accessions had similar total weights. The Colorado accession flowered earlier than other accessions. Seeds from Mississippi and North Carolina accessions grown in Colorado were heavier than the New Mexico or Colorado accession. This research demonstrates why making inferences of weed biology for variable species that occur over diverse geographic and climatic conditions is difficult and why regionally specific data are needed for variable species.

The influence of soil moisture on the competitive relationship between yellow nutsedge and cotton was determined in an additive competition experiment where main plots were irrigation regimes and subplots were nutsedge densities. Increasing nutsedge density caused a significant linear decrease in seed cotton yield. Regression analysis indicated that approximately 9 (1993), 12 (1994), or 37 (1995) kg ha−1 of seed cotton yield was lost for each additional initial nutsedge tuber per meter of crop row. Both postharvest stem biomass, an indicator of total aboveground biomass, and seed cotton yield increased with increasing soil moisture in all 3 yr of the study. Increasing yellow nutsedge density reduced midseason cotton height in both wet and dry soil moisture regimes but only slightly reduced postharvest stem biomass in the wet treatment in 1995. There was an interaction between soil moisture regime and yellow nutsedge density only with respect to midseason cotton leaf water potentials. Soil moisture availability did not interact with the effect of yellow nutsedge density with respect to end of the season stem biomass or seed cotton yield.

An accurate method is described for evaluating the relative effectiveness of isolates of Fusarium avenaceum as potential biological control agents for weeds such as spotted knapweed and wild oat. The method uses seeds that have been disinfected, placed in tubes containing water agar, and challenged with various isolates of F. avenaceum. Evaluatory data on the pathogenicity of the fungi are obtained after 14 d, when plants and fungi both are grown on water agar in the lab. Commonly, potential biocontrol agents are tested on seeds placed in the soil, but up to 60 d may be required for results. However, comparative studies using the soil test vs. the water agar test indicated that the water agar tests are giving comparable results to those from greenhouse tests but in a shorter time (14 vs. 60 d). Also, both water agar and soil tests were done with a number of crop plants including wheat, barley, alfalfa, and wild oat with comparable results. Thus, this method has the potential to screen many pathogens that may have potential biocontrol activities in a short time.

Field experiments were conducted at five locations in Colorado, Kansas, and Wyoming in 1994–1995 and 1995–1996 to compare the effects of MON 37500 rate and application timings on downy brome control and winter wheat tolerance. MON 37500 at 18 to 35 g ha−1 applied preemergence or fall postemergence reduced downy brome density 71 to 92% in 1995. Spring-applied MON 37500 suppressed downy brome growth but did not reduce plant density. No application reduced downy brome density in 1996. At each location, downy brome was controlled best by MON 37500 applied preemergence or fall postemergence at 35 g ha−1. MON 37500 did not affect wheat height at Archer or Torrington, WY, and Burlington or Stratton, CO, but wheat treated preemergence or fall postemergence was taller than untreated wheat at Hays, KS, in 1995. Spring-postemergence-treated wheat at Hays in 1995 was shorter than untreated, preemergence-, or fall-postemergence-treated wheat. Wheat head density did not differ among treated and untreated plots at Torrington, but herbicide treatment increased wheat yields. Wheat head density increased with all MON 37500 treatments at Hays in 1995, as did yield. However, preemergence and fall-postemergence applications resulted in the highest wheat yields. No herbicide treatment affected head density or yield at Hays in 1996.

Strategies for controlling invasive plants in northern Australian ecosystems must be designed to use limited resources. This paper examines the potential contribution of ecology to develop management strategies for Indian jujube, an invasive shrub in northern Australian tropical woodlands. Its fleshy fruits are dispersed by a variety of birds and mammals. Domestic cattle are the major dispersal vector, whose movements can be controlled at critical times to minimize the risk of new infestations. Containment of Indian jujube must include avoiding cattle movement from infested to weed-free paddocks and from infested to weed-free areas. The species has a capacity to sprout following topkill due to fire or mechanical treatment. This means that current options for effectively treating established plants are limited to the application of herbicides and the more expensive mechanical techniques. In single paddocks, concentrating limited resources on large reproductive plants may be more effective than concentrating on plants spatially peripheral to an infestation. At the property level, the first priority should be to prevent weed-free paddocks from becoming infested, the second should be to minimize increases in lightly infested paddocks, and the third to treat heavily infested paddocks that are major potential sources of new infestations. At the regional level, distributional outliers become important; their control may significantly reduce the length of the front from which local range expansion will occur.

Greenhouse studies were conducted with soil columns to determine the influence of rainfall amount, intensity, and time of application on the bioactivity of 0.07 kg ae ha−1 imazethapyr in three soils of New Jersey: the Berryland sand (BLS) (sandy, siliceous, mesic Typic Haplaquod), Aura sandy loam (ASL) (mixed, mesic Typic Hapludult), and Quakertown silt loam (QSIL) (mixed, mesic Typic Hapludult). The Brockman-Duke simulated rainfall machine was used for rainfall application and smooth pigweed as an imazethapyr bioactivity indicator. As rainfall amount increased from low to high (75 to 300 mm mo−1 equivalent) imazethapyr bioactivity declined significantly in BLS and ASL but was unaffected in QSIL. Rainfall intensity from 6 to 25 mm h−1 had no effect on imazethapyr bioactivity in the three soils. A delay in rainfall application up to 14 d after herbicide application significantly reduced the bioactivity of imazethapyr in BLS but had no effect in ASL and QSIL.

Tall fescue vegetative filter strips 0.5 to 4.0 m wide were evaluated for their ability to reduce losses of metolachlor, metribuzin, and runoff (water and sediment) in conventionally tilled soybean. Differences in the parameters studied were significant between filter and no filter strips, regardless of filter strip width. Two days after treatment, metribuzin concentration in runoff from the unfiltered treatment was 231 ng ml−1; filter strips reduced this amount to 119 ng ml−1 or less. Similar trends were observed with metolachlor, with concentrations of 1,009 ng ml−1 from the unfiltered, whereas filter strips of any width reduced this to 523 ng ml−1 or less. Metribuzin loss during the growing season was 41 g ai ha−1, or 9.8% of the amount applied when no filter strip was present. The addition of a filter strip, regardless of width, reduced cumulative metribuzin losses to 11 g ha−1 or less. Similar results were noted with metolachlor. Filter strips, regardless of width, reduced cumulative runoff and sediment loss at least 46 and 83%, respectively.

Substituted quinolinecarboxylic acids, including quinclorac (BAS 514H), are a new class of highly selective auxin herbicides, which are chemically similar to naturally occurring compounds isolated from plants and soils. Quinclorac is used in rice to control important dicot and monocot weeds, particularly barnyardgrass. The herbicide has also been developed for application in turfgrass areas, spring wheat, and chemical fallow. Quinclorac is readily absorbed by germinating seeds, roots, and leaves and is translocated in the plant both acropetally and basipetally. By mimicking an auxin overdose, quinclorac affects the phytohormonal system in sensitive plants. The compound stimulates the induction of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase activity and thus promotes ethylene biosynthesis. In susceptible dicots, increased levels of ethylene trigger an accumulation of abscisic acid (ABA), which, as part of the intrinsic auxin activity of quinclorac, plays a major role in growth inhibition and the induction of epinasty and senescence. In sensitive grasses, such as barnyardgrass species, large crabgrass, broadleaf signalgrass, and green foxtail, quinclorac leads particularly to an accumulation of tissue cyanide, formed as a co-product during increased ACC and ethylene synthesis. This causes phytotoxicity characterized by the inhibition of root and particularly shoot growth with tissue chlorosis and subsequent necrosis. These effects were not observed in tolerant rice and a resistant biotype of barnyardgrass. No significant differences in uptake, translocation, or metabolism of quinclorac between resistant and sensitive grasses were found. Hence, a target-site-based mechanism of selectivity is suggested. The induction process of the ACC synthase activity plays the primary role in the selective herbicide action of quinclorac. This is a common effect of auxin herbicides and auxins, which lead to the accumulation of cyanide and/or ABA depending on the plant species and tissues, the compound concentration in the tissue, and their biological activity.

Results from the “Potato Ecosystem Project,” a cropping systems study in northern Maine, were used to test the hypothesis that greater reliance on organic nutrient sources and less reliance on synthetic fertilizer sources can benefit weed management efforts. ‘Atlantic’ potato was grown in a 2-yr rotation within a factorial arrangement of three pest management systems, two soil management systems, and both rotation entry points. Weed control in the conventional (CONV) pest management system relied on full rates of herbicides, whereas the biointensive (BIO) system relied exclusively on cultivation. The reduced input (RI) pest management system relied on cultivation in 1991 and 1992 and on 50% of standard herbicide rates plus cultivation from 1993 to 1995. The two soil management systems, unamended (barley/red clover rotation crop; 1× synthetic fertilizer for potato) and amended (pea/oat/hairy vetch green manure rotation crop; manure, compost, and 0.5× synthetic fertilizer for potato) contrasted practices typical for the region to those designed to achieve rapid improvements in soil quality. Midseason weed biomass in potato was dominated by common lambsquarters. In 1991 and 1992, weed biomass in potato was least in the CONV system and did not differ between the RI and BIO systems. In 1993, weeds in both RI and CONV potatoes were effectively suppressed below the level measured in the BIO system. Soil management had no effect on weed biomass from 1991 to 1993 but became an important factor affecting weeds in the BIO system in 1994 and 1995. Weed biomass was 77% lower in 1994 and 72% lower in 1995 in the amended soil management system than in the unamended system. No significant yield loss due to weeds was detected in the 1994 BIO system, but in 1995 yield loss due to weeds was 37% in the unamended system compared to 12% in the amended system. Soil management effects on weeds in the 1994 BIO pest management system carried through to the following season's germinable seed bank. Density of germinable common lambsquarters seed (0 to 10 cm soil depth) in the 1995 BIO system was 4,082 m−2 in the unamended soil management system compared to 1,280 m−2 in the amended soil management system. We suggest that organic amendments and green manure promote a potato crop better able to compete with weeds and that these inputs be considered as potentially important components of integrated weed management systems that have minimal reliance on herbicides.

Field studies were conducted to determine the effect of common cocklebur interference in early-maturing (maturity group IV) soybean planted in April, May, and July. Common cocklebur density and length of interference did not affect soybean height, canopy width, or node number at any planting date. Removal of common cocklebur 4 weeks after emergence (WAE) prevented reduction of soybean leaf area, stem dry weight, dry leaf weight, dry pod weight, and seed yield. Aboveground biomass for common cocklebur emerging in July was less than biomass of April or May plantings. Common cocklebur planted into soybean 2, 4, or 8 wk after soybean emergence did not reduce soybean yield. Under parameters of this study, planting date was not a significant factor in yield reduction. Interference from one common cocklebur plant per 1.8, 0.9, and 0.3 m of soybean row for 8 wk reduced yields 7, 14, and 30%, and full-season interference reduced yields 16, 33, and 65%, respectively. The Arkansas Weed Management Computer program closely predicted actual yield loss for early-maturing soybean.

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.

Field and greenhouse experiments were conducted in 1995 and 1996 to determine soybean injury and weed control differences from imazamox and imazethapyr applied postemergence with a nonionic surfactant or methylated seed oil and with selected tank mixtures. Soybean injury from imazamox at 35 g ai ha−1 plus either a methylated seed oil or nonionic surfactant was equal to injury from imazethapyr at 70 g ai ha−1 in the greenhouse and field. Imazamox provided greater common lambsquarters control than imazethapyr in the field in 1995 and in the greenhouse. Thifensulfuron tank mixed with imazethapyr increased common lambsquarters control, while soybean response increased when thifensulfuron was tank mixed with imazamox. Common ragweed dry weight was reduced 61 to 64% from 35 g ha−1 imazamox and 70 g ha−1 imazethapyr in the field; however, imazamox provided greater common ragweed control than imazethapyr in the greenhouse. Tank mixtures of lactofen with imazamox or imazethapyr increased common ragweed control and resulted in greater soybean seed yield in 1996 than when imazamox and imazethapyr were applied alone; however, lactofen antagonized giant foxtail control with imazamox and imazethapyr, and antagonized common lambsquarters control with imazamox. Giant foxtail control in the greenhouse was antagonized more when acifluorfen, fomesafen, and lactofen were tank mixed with 35 g ha−1 imazethapyr than with 35 g ha−1 imazamox. Giant foxtail control with imazamox or imazethapyr applied alone or with diphenyl ether herbicides increased when 28% urea ammonium nitrate was added with nonionic surfactant compared with nonionic surfactant only. Imazethapyr antagonized giant foxtail control by clethodim in the field and was more antagonistic than imazamox in the greenhouse. A methylated seed oil improved common ragweed control by imazethapyr at 70 g ha−1 and imazamox at 18 and 35 g ha−1, while common lambsquarters and velvetleaf control increased when a methylated seed oil was included with 18 g ha−1 imazethapyr compared to nonionic surfactant in the greenhouse.

A hammer mill removed most of the lemmas, paleas, and pericarps from cheat florets. Typically, the cuticular layer of the testa was the only remaining intact layer, and damage to the embryos and endosperm was severe. A roller mill disrupted tissue organization of lemmas, paleas, and outer layers of the caryopses primarily at the cuts. Large gaps between the aleurone layer and testa, between testa and pericarp, and between the scutellum and endosperm were created. In the field, germination of mill-damaged florets was reduced, and florets exhibited progressive degradation the longer they were buried. Nematodes and fungi penetrated the cuticular layer of mill-damaged seed. Attaching a hammer mill or a roller mill to a grain combine to treat cheat seed before it is returned to the field could provide a novel method of cheat control.

Field studies were conducted at three locations in 1993 and 1994 to evaluate weed control and crop response to metolachlor plus combinations of 0.5 × and 1 × label rates of imazaquin applied preplant and imazethapyr applied early postemergence or postemergence in no-till narrow-row soybean production. Giant foxtail, common ragweed, common cocklebur, and large crabgrass population reductions were greater with sequential preplant metolachlor plus imazaquin followed by early postemergence or postemergence imazethapyr than with preplant metolachlor plus imazaquin or early postemergence/postemergence imazethapyr alone. Ivyleaf morningglory was not effectively controlled by any herbicide program. Pennsylvania smartweed populations were reduced with all herbicide treatments. Soybean yields with treatments utilizing 0.5 × rates were usually equal to 1 × rates if imazethapyr was applied early postemergence or postemergence. Net income with reduced herbicide rates was equal to full-label rates and provided no greater risk to net income.

A study was conducted to examine the effects of residence time and temperature on atrazine extractability and degradation in a sediment generated from Emporia sandy loam soil submerged under a water column. Sediments amended with 2.8 μg of atrazine were incubated at two temperatures (5 and 24 C), sampled at 0, 14, 28, 112, 168, 252, and 336 d, and then sequentially extracted once with 80 ml 0.01 M CaCl2 aqueous solution, three times with 25 ml of methanol/water mixture (4:1, v/v), and three times with 25 ml of methanol/water/formic acid (20:5:1, v/v pH 3.2) for a total of seven times. Extracts were analyzed for atrazine and metabolites using reverse phase high-performance liquid chromatography. The rate of bound residue formation was greater at 24 than at 5 C. About 30 and 60% of the 14C was bound (nonextractable) to sediments at 5 and 24 C, respectively. Water was less effective in extracting 14C residues from sediments incubated at 24 C than at 5 C. Acidification of the methanol/water mixture with formic acid during the last extraction step improved the removal of hydroxyatrazine from sediment. Atrazine degraded primarily to hydroxyatrazine (HA) and to a lesser extent to deethylatrazine (DEA). Although no DEA was found, HA at 43 μg kg−1 of sediment was detected 112 d after treatment at 5 C, indicating that chemical degradation could occur at a low temperature if sediments are incubated for extended periods of time. At 24 C, HA was found within 28 d and reached the maximum level at day 252. The results suggested that HA is the major metabolite of atrazine in the sediment; a significant fraction of the residue was unavailable for extraction, and this unextractable portion increased with residence time.

Cover crop residues are not widely used for weed control because, as a stand-alone tactic, they do not effectively suppress all weeds and their duration of weed control is too short. Field experiments were conducted in 1995 and 1996, under both irrigated and rainfed conditions, to quantify Amaranthus spp., Setaria spp., and soybean emergence and growth in residues of fall-planted, spring-killed barley, rye, triticale, wheat, and hairy vetch. For both weed species, seedling emergence was reduced 3 wk after soybean planting by rye and wheat residues (≥ 2, 170 kg ha−1) in 1996. In 1996, Amaranthus spp. canopy volume was reduced 38 to 71% by residues 3 wk after planting. Likewise, Setaria spp. canopy biomass was reduced 37 to 97% in residues 5 wk after planting over both years. The response comparison index was used to identify frequency by which weed growth was placed at a disadvantage relative to soybean growth. Amaranthus spp. and Setaria spp. growth suppressions 3 to 5 wk after planting indicate potential times for intervention with other integrated weed management tactics such as reduced postemergence herbicide rates and interrow cultivation.