Fungicides are only preventative and generally are not very effective in landscapes when conditions (e.g., susceptible plant material and wet conditions) favor gray mold development. Where gray mold has been a problem, the fungicides chlorothalonil, thiophanate methyl, or triforine can be applied before disease develops. For example, adequately space plants, prune canopies to eliminate some branches and foliage, and cut back nearby and overhead vegetation. Avoid wetting foliage, such as by using drip or microsprinkler irrigation. Remove and dispose of old blossoms, declining green plant tissue, plant debris, fallen leaves, and weeds. Use good sanitation practices and modify environmental conditions where feasible. Provide proper cultural care to keep plants vigorous. On roses large, diffuse, target-like lesions can form on green canes. When infected tissues are wet, commonly grayish fungal spores develop on the decaying tissue and give the tissues a fuzzy or woolly appearance. Affected plants develop spotted flower petals and leaves and infected buds can fail to open. Infection by Botrytis and Botryotinia species causes herbaceous plant parts to decay, discolor, and wilt. Gray mold is particularly troublesome under high humidity and moderate temperatures (70° to 77☏), but it is also active over a broader temperature range. Weeds and plant debris are common sources of gray mold spores, which are produced in enormous numbers and readily spread in air to nearby plants. Gray mold fungi do not infect woody parts.īotrytis and Botryotinia species can grow on almost any moist or decaying herbaceous vegetation. However, once petals or dead or weakened tissues are infected the fungus can move to invade adjacent, healthy green tissue that contacts diseased tissues. Healthy, actively growing green plant parts are seldom infected directly by these fungi. When humidity is high or plants are wet for at least 6 hours, declining or dying, soft tissues can become infected by airborne spores of Botrytis and Botryotinia species. Azalea petal blight, camellia petal blight, and rhododendron petal blight infect and kill only blossoms. However, Botrytis blight is a drier rot that also affects dying or inactive green tissue. However, Botrytis blight can occur anywhere plants are frequently wetted by overhead irrigation, especially those growing under crowded and shaded conditions where air circulation is poor.Īzalea petal blight and rhododendron petal blight and camellia petal blight when these hosts are involved can resemble Botrytis blight. Away from the coast, gray mold generally is a problem only during the late fall through early spring rainy season. In greenhouses or outdoors in coastal areas Botrytis and Botryotinia diseases can be a problem almost any time of year. Spores germinate and produce new infections only after plants have been continuously wet for 6 or more consecutive hours or when relative humidity has been higher than about 90% for 6 or more hours. Landscape hosts include azalea, bird of paradise, cacti, coast redwood, fuchsia, giant sequoia, hydrangea, rhododendron, and rose. Succulent tissue of most plants is susceptible to Botrytis blight. Infected fruit, leaves, petals, and succulent stems become dark, soft, and wilted and die. These infected spots turn brown and appear water soaked. Identificationĭisease often presents initially as tiny, almost translucent spots. Various Botrytis and Botryotinia species cause gray mold, most commonly Botrytis cinerea. The tiny, stalked spore-forming structures give rotted tissues a fuzzy appearance when viewed with the naked eye. Gray mold is named for the brown, gray, or tan fungal spores that develop on infected tissue when conditions are humid or moist. How to Manage Pests Pests in Gardens and Landscapesīotrytis blight, or gray mold- Botrytis and Botryotinia spp. UC IPM Home > Homes, Gardens, Landscapes, and Turf > Diseases
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