Leaf scorch of strawberries—Diplocarpon earlianum =Marssonina fragariae
Leaf scorch is a fungal disease that spots and kills strawberry leaves and reduces fruit abundance and quality.
Identification
Leaf scorch causes brown to purple spots on the upper surface of strawberry leaves. When infections are abundant, the leaf tissue between lesions commonly takes on a bright red to purplish color, but coloration varies with the cultivar, temperature, and other factors. Spotted leaves eventually turn brown, dry up, and curl at the margins, giving the leaf an overall burnt or scorched appearance for which the disease is named. Infected fruit may develop discolored streaks or sunken lesions.
Leaf scorch damage symptoms resemble those of common leaf spot, Mycosphaerella fragariae =Ramularia tulasnei. However common leaf spots have a sharply defined border while the borders of spots from leaf scorch are indistinct. Leaf scorch symptoms can also resemble other leaf spot diseases of strawberry.
Life cycle
The leaf scorch fungus overwinters in strawberry debris on soil and in strawberries grown as perennials. The small, asexual fungal fruiting bodies (acervuli) can continue to develop in decomposing, old foliage and overwintering strawberries. When conditions are wet during the spring, the fungus produces spores that are spread by splashing water and wind to infect strawberry plants. The development and spread of the fungus are favored by overhead irrigation and wet, warm weather. In addition to infecting leaf blades, the fungus can infect strawberry berry caps (calyxes), flowers, fruit stalks (pedicels), and leaf stems (petioles).
Damage
The disease is characterized by numerous small, brown to purplish lesions. Each spot on the upper surface of strawberry leaves commonly is 1/16 to 3/16 inch (1.5–4.5 mm) in diameter with indistinct borders. In severe infestations, infected flowers and fruit may die. Infected fruit can develop discolored, sunken lesions that make the fruit unappetizing even though it is still edible.
Solutions
Seek resistant varieties for planting where leaf scorch has been a problem or conditions are commonly wet. Grow strawberries as an annual so the fungus cannot persist in the same plant for multiple growing seasons and become more abundant over time.
Plant strawberries in a sunny, open location and on a berm or mound of raised soil. Avoid crowding plants and control nearby weeds. These cultural practices will increase air circulation around plants and can reduce the abundance of leaf scorch. Where the fungus has been a problem, remove all strawberry plant debris from the site at the end of the growing season and dispose of it away from where strawberries will be planted the next growing season.
To keep foliage drier, use drip or furrow irrigation instead of overhead sprinkling. Irrigate in the morning instead of late during the day or at night so that foliage dries more quickly. Where leaf scorch has been a problem, these recommended cultural practices (plant care activities, such as irrigation and planting methods) should provide good control.
Disease abundance also can be reduced by spraying thiophanate-methyl fungicide to thoroughly cover plants beginning during bloom. If wet conditions persist, repeated application at 2 week intervals may be warranted. For better control, use fungicide only in combination with the cultural controls described above.
Adapted from Diplocarpon earlianum, Wikipedia and Leaf Scorch of Strawberry, North Carolina State University. |
Strawberry leaves with spots and reddening due to leaf scorch fungus.
Strawberry leaves with purple spots due to leaf scorch fungus.
A brown leaf spot close-up showing black to dark brown fruiting bodies (acervuli) of the leaf scorch fungus.
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