Late spring rains have encouraged the development of several coastal crop diseases, including leaf blotch of strawberry. During the recent drought years this disease was rarely observed; however, leaf blotch (caused by the fungus Zythia fragariae) is showing up in strawberry fields this late spring. Symptoms on leaves will have tan to gray lesions (“blotches”) that usually first develop along the margin or edge of the leaflets (Photo 1). Such blotches are irregular in shape and may be surrounded by a purple border. These affected areas can expand and cover up to half of the leaflet surface. A notable feature of leaf blotch is the presence of tiny, brown, fungal fruiting bodies in the gray blotches (Photo 2).
Rain can splash Zythia spores from the leaves and onto the calyx tissue of fruit. The fruit calyx can become tan to brown in color, resulting in loss of quality of the fruit (Photo 3). Leaf blotch has been misdiagnosed as spray burn from chemicals, damage from high salt levels in the soil, the foliar phase of anthracnose disease, and even early season symptoms from Fusarium or Macrophomina. Examination of the leaves with a microscope is the best way to confirm leaf blotch.
Photo 1. Blotches often develop on margins of leaves.
Photo 2. Small dark fruiting bodies are usually visible.
Photo 3. The strawberry fruit calyx can also become diseased.