Phomopsis leaf blight of strawberry—Phomopsis (=Dendrophoma) obscurans
Phomopsis leaf blight is a leaf-spotting fungus that is an occasional problem in California strawberries. Other leaf spot diseases of strawberry are more common than Phomopsis leaf blight.
Identification
Phomopsis leaf blight first appears as circular, reddish to purple spots on mature leaves. As the lesions mature, the center of spots turn gray or tan, making them difficult to distinguish from common leaf spot of strawberry. Older lesions develop a characteristic pattern of three colors zones, commonly a pale brown or tan center surrounded by a brown ring that is surrounded by a ring of dark brown, red, or purple. Individual lesions grow to about 3/8 to 1/2 inch in diameter. On the upper leaf surface one or more tiny black fungal fruiting bodies (pycnidia) may develop in the center of lesions.
When abundant, lesions may grow together and form angular or V-shaped discolorations because spread of the infections is limited by major veins. The brown, V-shaped lesions may have a purple, red, or yellow border. When the pathogen infects daughter plants, runners, and stems it can cause dark lesions and these plant parts may die, resembling damage of anthracnose.
Life cycle
The Phomopsis fungus can be introduced in infected transplants from the nursery. It also overwinters in strawberry debris and the crowns of strawberries grown as perennials. The pathogen infects young leaves but its lesions do not develop until leaves become old. When the disease develops, it usually does so in late summer or fall. Once lesions develop, tiny spores are produced in the lesions and spread by splashing overhead irrigation and rainfall.
Damage
Phomopsis leaf blight causes discolored lesions in strawberry leaves. When this blight is abundant fruit yield may be reduced. If strawberry runners become infected daughter plants may wilt and die. However, Phomopsis leaf blight is not a common disease of strawberry in California.
Solutions
Obtain certified disease-free strawberry plants from a reputable, commercial supplier. Plant strawberries in a sunny, open location and on a shallow berm or mound of raised soil. Avoid crowding plants. Control nearby weeds. These practices will increase air circulation around plants, which can reduce the abundance of leaf spot diseases.
Use drip or furrow irrigation instead of overhead sprinklers. If irrigating overhead apply the water during the morning when foliage will dry more rapidly compared with evening or night. Carefully manage irrigation to avoid prolonged soggy soil (waterlogging).
At the end of the growing season remove and dispose of strawberry debris away from where strawberries will be grown the next season. Consider growing strawberries as an annual instead of a perennial.
Fungicides are generally not effective or warranted for Phomopsis leaf blight of strawberry in home gardens.
Adapted from Integrated Pest Management for Strawberries, University of California Statewide Integrated Pest Management Program (UC IPM). |
Leaf lesions of Phomopsis leaf blight.
Older lesions of Phomopsis leaf blight commonly have three color zones and develop black fruiting bodies in their center.
When Phomopsis leaf blight lesions grow together they commonly become dark and V-shaped, sometimes with a yellow margin.
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