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2022 Midwest Vegetable Guide

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Weed Management Strategies 56 Midwest Veg Guide 2022 Weed Management Strategies Reviewed by Dan Brainard – September 2021 Weed management requires a multifaceted approach built on an understanding of weeds and the crop. Successful weed management entails preventative strategies to reduce weed populations before planting, cultural practices to give crops a competitive advantage over weeds, and direct approaches including chemical physical, and biological tactics. The aim of any weed management strategy should be to manage the weed population so it is below a level that will reduce your economic return (economic threshold). It is important to consider the impact of weeds on yield and quality of the current crop, as well as the potential for increasing weed problems in future years if weeds go to seed. Deciding which methods to use depends on environmental concerns, marketing opportunities, desired management intensity, labor availability, weed pressure, and the crop. In some instances, the cost of controlling weeds may be more than the economic return from any yield increase that season. This situation occurs when a few weeds are present or the weeds germinate late in the season. In those instances, the best strategy may be to do nothing, or to do the minimum required to prevent seed production and dispersal. In other situations, weed populations and other considerations may require combining herbicides with nonchemical approaches. Weed Identification The first step in weed management is to identify the weeds and understand their life cycles and susceptibility to different weed management practices. Consult identification guides, such as Weeds of the North Central States (University of Illinois Agricultural Experiment Station Bulletin 772), for assistance. Weeds can be categorized by life cycles, and management strategies developed accordingly. Annual weeds complete their life cycles in one year and reproduce solely by seeds. Annuals can be divided into summer or winter annuals, depending on when they grow. Primary tillage operations often control winter annuals before a crop is planted in the spring. The most common vegetable crop weeds (e.g., barnyard grass, giant foxtail, crabgrass, common purslane, redroot pigweed, and common lambsquarters) are summer annuals. Perennial weeds live for more than two years and can reproduce by seed or vegetative structures (stolons, rhizomes, corms, bulbs, tubers, or roots). Because perennial weeds are difficult to manage in vegetable crops, it is usually better not to use a field with severe perennial weed problems. Among the most common perennial weeds encountered in Midwest vegetable crops are quackgrass, horsenettle, and yellow nutsedge. Many nonchemical weed management methods are common sense farming practices. These practices are of increasing importance due to consumer concerns about pesticide residues, potential environmental contamination from pesticides, and unavailability of many older herbicides. Prevention and Weed Seedbank Management Prevention is a critical component of successful weed management. Many weed species produce thousands of seeds that survive for decades in the soil, making up the weed seedbank. Avoiding "deposits" to the weed seedbank by preventing weeds from shedding seed is important for reducing the number of weeds emerging each year. This may mean mowing, tilling or applying herbicides after crop harvest to manage weed escapes, or planting a thick cover crop in non-crop areas to suppress weed growth and reproduction. The seedbank may also be depleted by encouraging "withdrawals" of seeds through repeated cultivation which stimulates seed germination and kills emerging weeds. Stale (or false) seedbed techniques aim to deplete weed seeds in the top few inches of soil through repeated shallow disturbance to stimulate seed germination followed by herbicide applications or flame weeding prior to planting the crop. This approach can be highly effective for late-planted vegetable crops such as fall carrots or beets, but is less practical for crops planted early in the spring. Additional details on weed seedbank management strategies can be found in the web resource, Manipulating Weed Seed Banks to Promote their Decline at eorganic.org/node/2807 . Cultural Practices Site Selection. Farm practices should aim to establish a vigorous crop that competes effectively with weeds. This starts with land selection. A general rule is not to plant vegetables on land with a history of heavy weed infestation, especially perennial weeds. Crop selection can reduce the effects of weed competition. One criterion in selecting a crop should be the weed problems of the field. Plant the most competitive crops in the most weed-infested fields, and the least competitive crops in the cleanest ones. Consider planting heavily infested fields as long-term set-aside acres or in non-row crops such as alfalfa. Permanent cover should help prevent buildup of annual weeds. Crop Rotation. Crop rotation is another practice that can reduce weed problems. The characteristics of the crop, the methods used to grow it, and the herbicides used, inadvertently allow certain weeds to escape control. Rotation also affects the weed management tools at your disposal.

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