Infection of leaves and inflorescences results from sporangia produced on living hosts. Life Cycle:ĭowny mildew overwinters on winter-sown host crops or cruciferous weeds. Disease can spread in storage and also may allow for entry of secondary rot pathogens. In advanced stages, the skin becomes rough and the root may split open, which can be confused with symptoms of Rhizoctonia root rot. Turnip or radish roots may develop internal, irregularly shaped brown or black discoloration extending from the crown downward. In cabbage, black spots may be evident on the exterior of the head, or internal darkening and purplish spots may occur if the infection becomes systemic and the pathogen is able to move from the lower leaves into the stem and head. In broccoli, there may be no spots on the head but gray streaks may form beneath the beads, running all the way back to the main stem. In cauliflower, dark gray spots may appear on the curd and, when cut open, gray streaking is noticeable on the branches beneath the florets. On older plants, these irregular yellow spots will become tan or gray papery patches. Under cool, moist conditions you may see white cottony growth on the undersides of leaves. These yellow lesions have networks of black spots or lines throughout, looking almost like a web. On seedlings, bright yellow, irregularly shaped spots appear on leaves. Heavy sporulation gives leaf undersides a gray to purple, downy appearance. These lesions enlarge and become irregular, yellow to orange necrotic patches, with dense sporulation on leaf undersides. Small, angular lesions develop on leaves and inflorescences. Infections that occur early in a crop life cycle may be latent or dormant, only showing symptoms later in the season when conditions in the field are again favorable. Disease development is favored by cool, moist conditions, whether moisture is from rain, dew, or fog. The disease caused by Hyaloperonospora brassicae s.l. is particularly important on seedlings but can also cause poor growth and reduced yield and quality of produce at later plant stages. Plants can be infected at any stage of growth. Downy Mildew occurs wherever brassica crops are grown and infects cabbage, Brussels sprout, cauliflower, broccoli, kale, kohlrabi, Chinese cabbage, turnip, radish, and mustard as well as cruciferous weed species.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |