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2022 Midwest Vegetable Guide

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Disease Management Strategies 46 Midwest Veg Guide 2022 Disease Management Strategies Reviewed by Dan Egel – September 2021 Plant diseases are caused by a wide variety of microbial pathogens (including fungi, bacteria, viruses, and nematodes). For a plant disease to occur, three components must be present: 1. The pathogen 2. A susceptible host (the plant) 3. An environment conducive to disease. In addition, insects spread some diseases, which makes them a fourth component of the disease cycle. Disease management strategies target one or more of those these factors to prevent and/or reduce the risk of disease. The sections below provide a broad overview of general management strategies. The crop-by-crop chapters go into much more detail for each disease. Disease Diagnosis Before making any management decisions, always make sure to correctly diagnose your problem first. Accurate diagnoses can save time and money because some diseases look alike but have very different management strategies. Different pathogens have different modes of both survival and spread. Therefore, certain management practices will work for some diseases but may have no effect on others. Furthermore, disease control materials are usually effective against only a subgroup of specific diseases. For example, fungicides will have no effect on viruses. Moreover, even among the various fungi, some materials may be effective against certain diseases but not others. In particular, the pathogens Pythium, Phytophthora, and the causal agents of downy mildews that we often discuss as fungi are not true fungi, they are in a different group of organisms called oomycetes. Many materials effective against true fungi are not effective for those organisms, and vice versa. For example, numerous materials used to manage downy mildew will have no effect or a negligible effect on powdery mildew, and vice versa. A root disease may require very different management compared to a leaf spot or fruit disease. Moreover, there are several plant health issues that mimic plant diseases (including environmental stress, nutritional problems, herbicide injuries, air pollution, and others). These are known as abiotic disorders. Unwittingly treating a nutrient deficiency with pesticides wastes time and money, and does not solve the underlying condition. Submitting samples to a diagnostic laboratory is the best way to ensure the correct diagnosis. For a list of labs and instructions on how to submit plants, see the State Contact Information table. Healthy Plant Material Contaminated seed or transplants can introduce diseases, so saving vegetable seeds for next year's crop is not recommended unless you are trained and equipped to handle seed sanitation. You should not save seeds when a seedborne disease has been active. The Summary of Cultural Management Strategies for Disease table lists some diseases that may be transmitted by seed to transplants. Whether you purchase transplants or produce them yourself, you should read Transplant Production to better understand transplant health. Be certain to inspect seedlings regularly. Examine the foliage and remove a few plants from the pots to inspect the roots. If you purchase transplants, keep newly- arrived materials away from other plants and the production area for a few days to prevent spread if a problem is found. Talk to your supplier and ask questions about how the reduce disease risk. If a you suspect a disease on received plants, take photos and contact a diagnostic laboratory, and continue to keep the plants separate. Keep good records of where plants are sourced from so that you can contact the supplier if a problem arises. Disease-Resistant Varieties Whenever possible, use varieties resistant to diseases. Some varieties may not be completely resistant to particular diseases; however, incomplete or partial resistance may be available. Some seed catalogs may refer to tolerance. The Summary of Cultural Management Strategies for Disease table presents information about the availability of resistant varieties. For certain vegetables (such as tomatoes) there are rootstocks available with resistance to some soilborne pathogens. A resistant rootstock may be an option if you have a history of a known soilborne disease but wish to grow a tomato scion variety that is susceptible. Tillage and Crop Rotation If a disease pathogen survives from year-to-year in crop residue or soil, then crop rotation and fall tillage are very effective factors in disease management. The pathogens are unable to survive once the crop residue decomposes.

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