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Extension > Garden > Yard and Garden > Fruit > Pest management in the home strawberry patch > Leaf spot

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Leaf spot

Mycosphaerella fragariae

Leaf spot was once one of the most common and destructive fungal diseases of strawberry. Severe infection on susceptible cultivars can result in death of leaflets and defoliation of plants. Many new strawberry cultivars, however, have resistance to leaf spot and the disease is no longer as common or as problematic as it once was.

Identification

leaf-spot

M.Grabowski, UMN Extension

In young infections of leaf spot, the white center may be difficult to see

leaf-spot

M.Grabowski, UMN Extension

leaf-spot

Foliage browning from leaf spot infection

Foliage browning from leaf spot infection

The leaf spot fungus can infect leaves, petioles, runners, fruit stalks, berry caps, and fruit. The symptoms of the disease begin with small purple spots on leaves or stems. The centers of leaf spots turn gray and then white with age. As the disease progresses multiple leaf spots merge together creating a reddish purple area with multiple round white centers. In severe cases, the leaves turn brown and die. Fruit infections are not common, but appear as small, sunken, leathery, black spots on unripe and ripe fruit. Seeds within the infected area of the fruit turn black.

Important biology

The leaf spot fungus overwinters on infected living leaves and in leaf debris. Spores are produced from both of these sources in the spring, and are spread to healthy tissue by splashing rain or irrigation. Cool temperatures (68 to 77o F) and long periods of leaf wetness (>12 hours) are required for new infections to develop. Consecutive wet days with temperatures between 50- 86o F favor disease development. The disease will progress as long as temperature and moisture are in acceptable ranges.

Management

Resistant cultivars

Many strawberry cultivars commonly grown in Minnesota have some ability to tolerate leaf spot infection. Although leaf spots may be observed on foliage, the damage is typically not severe enough to reduce yield.

Cultural control

Fungicide use

Fungicides are rarely necessary to control strawberry leaf spot. The cultural control practices listed above typically reduce disease to a manageable level.


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