Leaf blotch of strawberry—Zythia fragariae =Gnomonia comari
Leaf blotch is a fungal disease that occurs occasionally on strawberries in California. Other leaf spot diseases of strawberry are more common than leaf blotch.
Identification
Infection by Z. fragariae causes gray to tan blotches on young leaves of strawberry. Lesions generally develop on the outer margins of leaflets, are irregular shaped, and may develop a purplish margin. Affected areas commonly grow to cover 1/4 or more of a leaflet's surface. A diagnostic feature of leaf blotch is the presence of numerous tiny, dotlike black to brown fungal fruiting bodies in gray to tan blotches. Lesions on older leaves can resemble lesions of Phomopsis leaf blight. Black lesions from Z. fragariae can develop on leaf blades and stems.
Where plants are irrigated overhead, brown to tan lesions can develop on the fruit calyx (the berry caps, or green whorl of leafy material on top of the fruit). Zythia fruiting bodies sometimes develop in the calyx lesions and are dark brown, circular to oblong structures. When calyx lesions appear, there are generally also lesions on leaves.
Life cycle
The pathogen survives on plant debris and in other Rosaceae plants that are infected. When the fungus causes infections, it generally does so in late winter to early spring. Leaf blotch development is favored by overhead irrigation and rainy weather. Once the rainy season ends the fungus no longer causes new infections. Plants then grow out of the problem and there is generally no active disease by the time fruit develop. An exception is when strawberry is irrigated with sprinklers; this can cause the pathogen to be active anytime Rosaceae host plants are present.
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 the evening and 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.
If the above cultural control methods are practiced, leaf blotch is generally not an important disease and does not affect fruit yield. Fungicides are generally not effective or warranted for leaf blotch of strawberry in home gardens.
Adapted from Unusual Flare-up of Leaf Blotch Disease of Strawberry, University of California Agriculture and Natural Resources and Integrated Pest Management for Strawberries, University of California Statewide Integrated Pest Management Program (UC IPM). |
Leaf blotch lesions are gray to tan, irregular shaped, and generally develop on leaflet margins.
A leaf blotch lesion with numerous, tiny, dark fungal fruiting bodies.
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