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2022 Midwest Vegetable Guide

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Disease Management Strategies Midwest Veg Guide 2022 47 Tillage (especially fall tillage) helps control diseases by reducing the amount of inoculum (pathogen structures) that survives the winter. Rotating fields to different crop families each year also helps control diseases by preventing the build- up of certain plant pathogens in the soil. Summary of Cultural Management Strategies for Disease provides tillage and crop rotation recommendations. A general rule is that you should not rotate a field to a crop in the same botanical family. Unfortunately, there are several kinds of soilborne diseases that are unaffected by rotation. The first group of these diseases is caused by pathogens that produce resilient survival structures that can withstand the effects of time and nonhost crops. Two such diseases are Fusarium wilt, and root-knot nematode. Another group of diseases unaffected by crop rotation has a broad host range, so they can survive indefinitely on many host crop and weed species. Examples include Sclerotinia, Rhizoctonia, and Verticillium diseases. In addition, root-knot nematode can cause disease in multiple vegetable plant families (cucurbits, tomato, carrot, and many more) along with some field crops and even weeds. The third group of diseases unaffected by rotation overwinter in Gulf Coast states, and then spread north by wind during the growing season. Examples include sweet corn rust and downy mildew of cucurbits. In addition, certain viruses spread by highly motile insects (such as aphids), so rotation does not reduce these diseases either. Since the pathogen does not overwinter locally in the field, survival in residue is not a factor. Consider all options before making management decisions. Rotation is a good general practice that improves or maintains good soil tilth. Tillage (especially fall tillage) often is not in accord with recommended soil management and conservation practices. If you practice no-till or reduced tillage, you will need to be even more vigilant with other strategies in order to reduce your risk of disease. Two publications that may be useful for no-till or reduced tillage growers are Building Soils for Better Crops: Sustainable Soil Management and Managing Cover Crops Profitably, both available from the Sustainable Agriculture Research & Education (SARE) Learning Center, Water and Humidity Management Many bacterial and fungal pathogens thrive in wet conditions. Certain soilborne pathogens such as Phytophthora and Pythium species are favored by wet soils with poor drainage. Avoid planting into sites with known drainage problems. Improve drainage, and consider using raised beds. Many leaf spot and fruit rot diseases are favored by high humidity and wet plant surfaces. Using drip irrigation instead of overhead irrigation will reduce leaf wetness. If you use overhead irrigation, irrigate in the morning so that plant surfaces dry before nighttime. Avoid overhead irrigation in the evening. Reduce plant density to allow better airflow and sunlight to penetrate, which will decrease leaf wetness and humidity. With certain crops (such as tomato) appropriate staking or trellising will also increase airflow. Reducing weed pressure in and along the sides of the crop can also improve airflow. Align rows to maximize airflow and sun exposure. In greenhouses and high tunnels, use passive ventilation and/or fans to reduce humidity. See Transplant Production for details about water and humidity management in that setting. Avoid working wet fields. Scouting and Sanitation Depending on the disease and the size of your operation, you can and should rouge (remove) infected plants. For example, there are no treatments for viral diseases, so you should remove infected plants to reduce the spread to other plants. Bacterial canker of tomato is another disease where you should rogue out the infected plants and several neighboring plants. Flag the area and come back to check for further spread. Culls should be removed far from the field. In greenhouse situations, remove the trash frequently, and always keep lids on trash cans to prevent pathogens (and insects) from building up in discarded plant materials. For some crops (such as tomato) stakes and trellises can harbor certain bacteria from one crop to the next. So always use new stakes, or at minimum disinfest them. Disinfest tools frequently, such as at the end of rows. Avoid working fields under wet conditions. Other Cultural Practices Insects (such as thrips, aphids, cucumber beetles, and others) spread numerous diseases, so cultural practices that reduce the insects will reduce the risk of diseases. The comments for the Summary of Cultural Management Strategies for Disease table lists some of these practices. See the Insect Management Strategies section for guidelines about cultural controls to reduce insects that may spread diseases.

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