![]() ![]() In hostas, it appears the age of plants is not a factor in Botrytis infection. The lesions can spread down the leaf petiole and sometimes can be found beneath the soil surface. The dark fungus often can be seen on the underside of the lesion, especially early in the morning when the leaves are still wet. As the lesions mature and increase in size, rings can be seen within the lesions, which appear cinnamon to dark tan in color. In hostas, immature lesions appear mostly as water-soaked spots that increase in diameter to become circular spots with dark halos around the outside. In the presence of inoculum, when conditions are favorable for development of Botrytis and the plant is susceptible, botrytis blight can occur. In commercial nursery fields and shade houses, the practice of growing plants close together creates a humid environment, which is ideal for the development of botrytis blight. This year, the weather has been conducive for infection with the common plant pathogen Botrytis cinerea ( view photos). Check the label of any pesticide referenced to ensure your use is included. Be sure to read and follow all label instructions of the fungicide that you select to insure that you use the fungicide in the safest and most effective manner possible.Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. However, Botrytis may develop resistance to these products (particularly iprodione). ![]() Fungicides such as chlorothalonil, iprodione and mancozeb can be used to prevent infections. ![]() Reduce humidity around plants and germinate seedlings under warm, relatively dry conditions. Avoid wounding plants mechanically, or chemically by overfertilization or misuse of pesticide sprays. How do I avoid problems with gray mold in the future? Remove dead or dying tissue from plants and the soil surface. Disinfest pruning tools between cuts by dipping them for at least 30 seconds in a 10% bleach solution or alcohol (spray disinfectants that contain at least 70% alcohol can also be used). Prune diseased branches four to six inches below the infection leaving a clean cut. How do I save a plant with gray mold? Promptly remove diseased leaves and flowers. In order to infect tough tissues such as healthy leaves, Botrytis spores require an external food source such as nutrients leaking from wounds or dying tissues such as old flower petals. Botrytis spores rapidly die when dried, and most readily infect delicate tissues such as petals. Botrytis produces large numbers of dusty, gray reproductive spores that are spread by wind or splashing water. Where does gray mold come from? Gray mold is caused by the fungus Botrytis cinerea, which survives on dead plant tissue as dark brown to black, multi-celled structures called sclerotia, and as thick, dark-walled, single-celled spores called chlamydospores. Botrytis can also cause stem cankers (localized sunken areas) that may eventually enlarge to girdle the stem. On leaves, Botrytis causes irregularly-shaped necrotic (dead) areas that may have a bull’s-eye pattern. On plants such as tulips, crocus, and daffodils, gray mold may spread from flowers into the bulbs leading to bulb decay. Early infections may prevent flowers from opening. What does gray mold look like? Gray mold causes brown spots on petals that enlarge, killing the petals, and eventually the rest of the flower. Gray mold is a particularly serious problem on flowering plants and those plants grown in greenhouses. What is gray mold? Gray mold (or Botrytis blight) is a common and often serious fungal disease that can affect plants of all kinds. Jeffory Schraufnagel*, Milwaukee Area Technical College, Brian Hudelson, UW-Madison Plant Pathology Severe gray mold can prevent rose blossoms from developing properly. ![]()
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