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2022 Midwest Vegetable Guide

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Transplant Production Midwest Veg Guide 2022 25 Damping-off may occur before or after seedlings emerge from the soil. Preemergence damping-off occurs when fungi infect seeds as they germinate. As infections progress, seeds rot and eventually disintegrate. Poor stands become apparent after several days or weeks. Postemergence damping-off is usually observed in seed flats or among transplants. Fungi infect stems at or near the soil surface. The affected area of the stem takes on a water- soaked appearance and sometimes becomes constricted. Eventually, the stems are unable to maintain the structural support of seedlings, which usually collapse and die within 24 to 48 hours. Several soilborne fungi cause damping-off on vegetables. Fusarium, Phytophthora, Pythium, and Rhizoctonia species are well known causal agents of pre- and postemergence damping-off. Control measures to prevent damping-off diseases include: • Using uncontaminated soil mix. Use a commercially prepared soilless growing mix sold in 3 to 4 cubic foot bales or bags. A common mistake is to open a bag of "clean" soil mix and place it on a dirty floor or some other unclean surface prior to planting. Remember that your soil is only as clean as the dirtiest surface it has contacted. • Planting seeds shallow and in warm soil. • Using soil mixes that drain well. Seedborne and residueborne diseases affect most vegetable crops. The pathogens (disease-causing microorganisms) survive in or on seeds or plant residues, not in soil mixes. Outbreaks of these diseases often show up as clusters of diseased plants, and symptoms often include brown lesions with yellow halos on leaves. By contrast, environmentally induced problems often occur uniformly throughout the seedlings or only in one location (for example, close to an outside wall). Several different fungal, bacterial, or viral pathogens may be introduced into a transplant facility via contaminated seed or transplants (Common Seedborne Diseases of Vegetable Crops Frequently Grown as Transplants). Once introduced, these pathogens may continue to cause problems year after year if proper precautions are not taken. Common Seedborne Diseases of Vegetable Crops Frequently Grown as Transplants Vegetable Crop Disease cabbage Alternaria leaf spot, black rot cantaloupe anthracnose, gummy stem blight cucumber angular leaf spot pepper bacterial spot squash squash mosaic (squash mosaic virus) tomato bacterial canker, bacterial speck, bacterial spot watermelon anthracnose, gummy stem blight, bacterial fruit botch Several measures should be taken to minimize or prevent introducing seedborne or residueborne pathogens into a transplant facility: • Avoid saving seed unless you are specifically trained and equipped for seed production. • Inspect seedlings frequently while they are growing. • Separate seedlots from one another. Save all information regarding seed purchases. • Irrigate in the morning to ensure soil and leaf surfaces dry. • Check fungicide and bactericide labels for specific mentions of greenhouse use when treating transplants (see the Conversions for Liquid Pesticides on Small Areas table, in the Pesticide Application and Safety section, for liquid pesticide conversions). • Practice good sanitation. Plant pathogens often survive in soil and plant residues. Therefore, sanitation is as important for a greenhouse as it is for a kitchen. Greenhouse floors should be as free of soil and residue as possible; plastic or cloth floor coverings provide a barrier between dirt floors and transplants. Transplant trays and flats should be new or cleaned and disinfected before each transplant generation. More detailed information about disease prevention and control in the greenhouse is available in Preventing Seedling Diseases in the Greenhouse (Purdue Extension publication BP-61-W), and Commercial Greenhouse and Nursery Production: Sanitation for Disease and Pest Management, available from the Purdue Extension Education Store (HO- 250-W), . A few chemicals are labeled for disease control in greenhouse vegetable crops. Restricted use pesticides can only be used by certified pesticide applicators who have the greenhouse certification on their applicator licenses. Restricted use pesticides are identified prominently on the label. If a pesticide is not restricted use and is labeled for the crop in question, check the label. If it does not mention greenhouse use, then it may be used in greenhouses. Otherwise, the label may explicitly prohibit greenhouse use. Thus, a specific label for greenhouse use for some products is not required; but you must carefully read each label to be certain the greenhouse

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