Experiments were conducted in North Carolina in winter/spring 1992, 1993, and 1994 to determine crop tolerance, weed response, and clopyralid residue levels in fruit of ‘Chandler’ strawberry plants treated with clopyralid. Clopyralid at 0.07, 0.14, 0.20, or 0.28 kg ai ha−1 applied POST over strawberry plants and vetch resulted in 100% control of vetch species, 49 to 83% control of black medic, and less than 6% crop injury. As a comparison, 2,4-D at 0.84 kg ai ha−1 applied POST at 5 to 10% strawberry bloom resulted in 50% control of black medic and 48 to 73% crop injury, while 2,4-D at 0.84 kg ai ha−1 applied POST to 7- to 9- and 9- to 10-leaf strawberries resulted in 5 to 22% crop injury and no adverse affect on strawberry yield. Single applications of clopyralid at 0.07, 0.14, or 0.28 kg ai ha−1 applied POST to weed-free strawberries at the 5- to 6-, 6- to 7-, 9- to 10-, or 12- to 14-leaf stage caused less than 6% injury and did not adversely affect strawberry yield. In 1993 with preharvest intervals (PHI) of 39, 66, and 101 d after treatment all clopyralid residue levels in strawberry fruit were below the detectable level of 0.3 parts per billion (ppb). In 1994, with PHI of 30, 59, and 87 d after treatment trace clopyralid residues were found in strawberry fruit with a range from 0.25 to 1.9 ppb, with a level of detection of 0.2 ppb.

Studies were conducted at the Main Agricultural Experiment Station in Fayetteville and the Vegetable Substation in Kibler, Arkansas, in 1992 and 1993 on the same plots to evaluate weed suppression by winter cover crops alone or in combination with reduced herbicide rates in no-till sweet corn and to evaluate cover crop effects on growth and yield of sweet corn. Plots seeded to rye plus hairy vetch, rye, or wheat had at least 50% fewer early season weeds than hairy vetch alone or no cover crop. None of the cover crops reduced population of yellow nutsedge. Without herbicides, hairy vetch did not suppress weeds 8 wk after cover crop desiccation. Half rates of atrazine and metolachlor (1.1 + 1.1 kg ai ha−1) reduced total weed density more effectively in no cover crop than in hairy vetch. Half rates of atrazine and metolachlor controlled redroot pigweed, Palmer amaranth, and goosegrass regardless of cover crop. Full rates of atrazine and metolachlor (2.2 + 2.2 kg ai ha−1) were needed to control large crabgrass in hairy vetch. Control of yellow nutsedge in hairy vetch was marginal even with full herbicide rates. Yellow nutsedge population increased and control with herbicides declined the second year, particularly with half rates of atrazine and metolachlor. All cover crops except hairy vetch alone reduced emergence, height, and yield of sweet corn. Sweet corn yields from half rates of atrazine and metolachlor equalled the full rates regardless of cover crops.

The goal of this research was to determine whether crop management practices could substitute for a herbicide for managing mixed populations of green and yellow foxtail in hard red spring wheat. Crop yield and foxtail growth were measured in two years of field research in North Dakota. Spring wheat yields were as great or greater when early seeding date or 2× seeding rate were substituted for POST diclofop3 at 0.75 kg ai ha−1 for managing foxtail in spring wheat. Yield of spring wheat competing with foxtails was greater for the high seeding rate (2× = 270 kg ha−1) than both the normal (1× = 130 kg ha−1) and low (0.5× = 70 kg ha−1) seeding rates for early or middle seeding dates, but not for the late seeding date. For both early and middle seeding dates, wheat yield at the 2×seeding rate without diclofop was equal to or greater than that of the 1× seeding rate with diclofop. Late-seeded wheat did not yield well in competition with dense foxtail stands for any treatment combination. Early and middle seeding dates favored the relative increase of green foxtail over yellow foxtail in wheat, whereas late seeding favored yellow foxtail over green foxtail. Economic analysis demonstrated that early seeding date was the most critical factor in determining the stochastic dominance of treatments without diclofop over treatments with diclofop. Seeding rate was much less important than seeding date in determining the ranking of treatments in stochastic dominance analysis.

Additional information on mechanical weed management systems is needed so producers can develop systems that meet their production and weed control goals without sacrificing profitability. Field research was conducted at Rosemount, MN, in 1989, 1990, and 1991 to determine the effect of preplant tillage and soybean planting date on weed populations and effectiveness of mechanical weed control operations. Delaying soybean planting from mid-May to early-June reduced weed densities and yield losses from weeds. Weed control with a herbicide treatment was not affected by planting date, but control with rotary hoeing and cultivation was often increased by delaying soybean planting. Early-planted soybean usually yielded better following herbicide treatment than mechanical weed control. However, when preplant tillage and planting were delayed, weed densities were reduced and mechanical weed control operations usually resulted in soybean yield similar to the herbicide treatment. While delaying soybean planting reduced weed densities and improved mechanical weed control, there is potential for reduced soybean yields with delayed planting.

Greenhouse experiments determined differences in imazaquin bioavailability over time under various soil moisture regimes. All soils were initially fortified with 63 ppb (w/w) of commercially formulated imazaquin. Treatments consisted of maintaining at field capacity for 15 wk (FC), maintaining air-dry for 15 wk (AD), soil that was maintained air-dry for 2 wk and then wet to field capacity at 2 wk intervals (2WAD), and soil that was wet to field capacity at the initiation of the experiment and at 2 wk intervals (2WFC). Little dissipation of imazaquin occurred in the AD soil over the 100 d of this study. Rapid dissipation over the first 35 d occurred for the other three treatments. Imazaquin half-life ranged from 17 to 18 d for the FC, 2WAD, and 2WFC soils. Imazaquin concentration increased or only slightly decreased in samples taken after the second watering in both the 2WAD and the 2WFC soils. Due to differences in adsorption/desorption of imazaquin with changing soil moisture levels, bioassays may not determine the dissipation of the actual concentration of imazaquin contained in soil.

Phytotoxic effects of metabolites from a naturally occurring rhizobacterial isolate, Pseudomonas syringae strain 3366, were determined on downy brome and ‘Hill 81’ winter wheat, along with 10 other weed and crop species. Centrifuged supernatant and concentrated ethyl acetate extracts from aerobic shake cultures of strain 3366 suppressed germination of seeds and reduced root and shoot growth in agar diffusion assays, soil assays, and under field conditions. Generally, root growth was inhibited more than shoot growth. Strain 3366 metabolites applied in soil inhibited all species tested. Crude ethyl acetate extracts in soil inhibited downy brome at concentrations that had little effect on winter wheat. Inhibitory activity was greater in Palouse silt loam (pH 5.8, 3.6% organic matter) than in Shano silt loam (pH 9.0, 0.8% organic matter). Activity of extracted metabolites decreased rapidly in wet soil but remained high in dry soil. Active metabolites were isolated and purified from the ethyl acetate extract using column chromatography, thin-layer chromatography, and crystallization. Chemical analysis revealed the presence of phenazine-1-carboxylic acid, 2-amino phenoxazone, and 2-amino phenol. Activity of these metabolites against downy brome was confirmed in agar assays. Phenazine-1-carboxylic acid, the major identifiable metabolite present in ethyl acetate extracts (20% by weight), inhibited downy brome root growth by 99% at concentrations of 5.7 mg L−1. Production of these metabolites in field soil by live bacteria of strain 3366 was confirmed with thin-layer chromatography.

The study was undertaken to compare the level of total phenolics and the allelopathic potential of Pluchea lanceolata in soils cultivated once or twice a year. Thirty-five cultivated fields were sampled from seven sites in three different seasons. The leaf area, leaf weight, height, and density of P. lanceolata plants were measured. Leaves of P. lanceolata were analyzed for nine chemical characteristics: leaf ash, total phenolics, phosphate, Cu, Zn, Na, K, Mg, and Ca. Weed-infested topsoil and subsoil were analyzed for pH, electrical conductivity, organic carbon, chloride, bicarbonate, total carbonate, phosphate, total phenolics, Zn, Na, K, Mg, and Ca. Fields cultivated twice a year were designated as Group I, while those cultivated once a year were designated as Group II. Biotic and chemical characteristics of plants of Group I and II were not different. Topsoil and subsoil of Group II had higher values for Ca, while topsoil of Group I had higher values for total phenolics. The higher phenolic content of Group I topsoil was probably due to greater incorporation of weed plant parts into the soils as compared to Group II fields. Seedling growth of crop plants such as radish, carrot, maize, mustard, tomato, turnip, and wheat was affected more by soil from P. lanceolata-infested fields that were cultivated twice a year than those cultivated only once. A correlation between higher total phenolic content of P. lanceolata-infested topsoil with two cultivations, and growth response of crop plants was recorded.

In greenhouse studies, overhead watering or subsurface irrigating soil can cause fluctuating moisture content, as can treatments such as surface application of residue used in cover crop research. This paper introduces a method of capillary mat subirrigation that maintained soil moisture at about field capacity for 16 d while no moisture could be detected after 6 d in soil placed under similar conditions that was not irrigated. In another study, subirrigation eliminated differences in soil moisture due to the presence of surface-applied residue and moisture supplied by hand watering from overhead was apparently removed from subirrigated treatments, which never differed in soil moisture content.

Greenhouse experiments that used capillary mat subirrigation to maintain constant soil moisture and to supply fertilizer continuously were conducted to evaluate the effects of sorghum or rye residue on early growth of barnyardgrass and velvetleaf. The separate effects of root residue and of shoot residue were compared to the combined effects of root plus shoot residues and to an uncovered soil control. Residues included as nontoxic controls were leached shoot tissue and poplar excelsior. Shoot residue, leached shoot tissue, and poplar excelsior were surface-applied on an equal light transmittance basis such that mass of poplar excelsior > shoot residue > leached shoot tissue. The presence of rye root residue delayed emergence of barnyardgrass. Surface-applied residues tended to decrease barnyardgrass height, but velvetleaf stem length was greater in treatments with surface residue. Although cover crop shoot residues had little effect on weed growth after 18 d, weed growth decreased in the presence of cover crop root residues and poplar excelsior.

Integrated Weed Management (IWM), a long time practice by farmers has become more commonly discussed as a total weed management system. Whether an off shoot of Integrated Pest Management (IPM) or a further recognition of integrating weed control measures within the cropping and farming system, it has become more widespread. IWM is being practiced using many of the same components, from croplands to forests and rangeland. A weed management hierarchy has been developed by degree of diversity of management practices. IWM researchers and educators should invite other pest management specialists to join us in striving for Integrated Crop Management systems.

Planting row crops into a stale seedbed has gained popularity in recent years. This concept uses tillage either after harvest in the fall or early in the spring to smooth the seedbed and eliminate ruts and excess residue on the soil surface. Tillage is not used immediately before planting, thus conserving moisture, eliminating costly and time-consuming tillage trips at planting, and allowing more timely planting. While stale seedbed planting minimizes tillage to establish the crop, conservation is not the primary objective of this concept; rather, timely stand establishment following adverse weather conditions has been the driving force behind the popularity of stale seedbed programs. The stale seedbed approach has been used with success on a variety of soils in the southern U.S., but is best suited on the poorly-drained clay soils in the Mississippi River Delta. The system has been adapted for use in soybean, cotton, corn, and rice. A key component of a well-prepared stale seedbed is the absence of weeds at planting. Producers must keep in mind that weeds present and not controlled at planting have the potential to significantly impair stand establishment and crop yields. Although these weeds are often beginning to senesce by the time soybean planting occurs, they are still using soil moisture and shading newly emerging crop plants early in the season.

Ridge-till is an integrated weed management system that involves the physical movement of soil containing weed seeds away from the row with ridge-clearing equipment on the planter. Corn, grain sorghum, and soybean are the major crops planted using the ridge-till system. Weeds can be controlled with cultivation, competitive row crops, and herbicides. Weeds have adapted to the system but have been controlled through alternative management. Through modernization of equipment and herbicides, ridge-till has become an economic crop production practice. Integrating cultivation and herbicides controls a broader spectrum of weeds than cultivation or herbicides alone.

Cooperative research was initiated by a multidisciplinary team of weed scientists and agricultural economists in 1975 that laid the foundation for integrated weed management research in Colorado. Colorado's integrated weed management research has four phases: weed seed bank decline, systems approach to weed management, bioeconomic modeling, and multiple weed management tactics. Each phase considered weed seed bank, weed control efficacy, weed control costs, crop yield, and gross margin. All four phases emphasize the need for a weed management system that minimizes seed production in situations where a high soil weed seed bank exists. However, once the weed seed bank is reduced, a weed management program with less than 100% weed control can be employed without increasing the seed bank. Intensive weed management systems are seldom justified when economics, weed control, and weed seed bank are considered. Integrated weed management approaches require integrating crop and weed biology with management tactics. Integrated weed management requires advanced managerial skills and often more time than traditional approaches.

A 9-yr large-scale integrated pest management (IPM) study was initiated in 1985 to develop and refine profitable conservation cropping systems in the Palouse wheat-growing region of the Pacific Northwest. Weed scientists from the USDA-ARS and the land-grant universities of ID and WA led a team of researchers and extension personnel from eight disciplines to investigate the interactions of crop systems, tillage systems, and weed management levels (WML) on crop production. Ineffective weed control has been a major deterrent to the adoption of conservation tillage by wheat growers. With this in mind, the primary focus of the scientists on the IPM project was integrated weed management (IWM) in conservation crop production systems for highly erodible land. For the first time in the Pacific Northwest, systems research developed a conservation production system using a 3-yr crop rotation that controlled weeds effectively, reduced erosion, was less risky than traditional farming systems, and was profitable. Broadleaf weeds were more prevalent in the 3-yr rotation of winter wheat-spring barley-spring pea compared to continuous wheat in both conservation and conventional tillage systems. In conservation tillage, troublesome grass weeds included wild oat and downy brome. Wild oat was controlled effectively at the moderate and maximum weed management levels under conservation tillage in the 3-yr rotation. Two years out of winter wheat (such as in the 3-yr rotation) reduced downy brome populations. In contrast, growing a spring crop 1 yr, followed by 2 yr of winter wheat was not effective for controlling downy brome. Effective weed control was instrumental in developing successful conservation IPM cropping systems, and education and technology transfer were important in helping action agencies assist growers in adopting these systems.

Integrated weed management (IWM) research has focused on how crop yields and weed interference are affected by changes in management, e.g., tillage, herbicide application timing and rates, cover crops, and planting patterns. Acceptance of IWM will depend on recommendation of specific strategies that manage weeds and maintain crop productivity; such research will and should continue. However, IWM needs to move from a descriptive to a predictive phase if long-term strategies are to be adopted. Linking management changes with crop-weed modeling that includes such components as weed population dynamics and the ecophysiological basis of competition will help predict future weed problems and solutions and the economic risks and benefits of intervention. Predictive approaches would help incorporate IWM into models of the processes that occur in agricultural systems at wider spatial and temporal scales, i.e., in agroecosystems comprised of the interactions among organisms (including humans) and the environment. It is at these larger scales that decisions about management are initiated and where questions about the long-term consequences and constraints of IWM and agriculture are often asked. These questions can be addressed by agroecosystem health, an approach that integrates biophysical, social, and economic concerns and recognizes that agriculture is part of a world with many complex subsystems and interactions. Indicators are used to examine the status of an agroecosystem, e.g., whether or not it contains all that is necessary to continue functioning. Indicators include soil quality, crop productivity, and water quality; all of these are related to the rationale of IWM, hence IWM can be linked to agroecosystem health. Ancillary effects of using IWM relate to other indicators such as diversity and energy efficiency. Linking IWM to agroecosystem health has at least two benefits: (1) predictive models within IWM can be incorporated into larger agroecosystem models to explore hitherto unforseen problems or benefits of IWM, and (2) the relevance and benefits of IWM should become clearer to the public and government agencies who otherwise might not examine how IWM promotes many of the larger social, economic and environmental goals being promulgated.