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Control strawberry diseases now for next year

Whether you raised your own strawberries or bought them, this was an excellent year to eat strawberries. Before you abandon your patch for another year, there are some jobs that need to be done at this time to be sure that you will have a nice patch next year, you need to check for disease and renovate June bearing plants.

Michelle Grabowski, Regional Extension Educator, states that strawberry leaf spot, leaf scorch, and leaf blight are common fungal diseases in Minnesota.

All three fungi survive our winters in the mature perennial leaves of the strawberry plants or in leaf debris in the strawberry patch. Spores are spread by splashing water or by wind to start infections on new leaves early in the growing season. Although disease may not seem severe at this time, the fungi will continue to grow and spread all season long whenever the weather conditions are favorable. This can result in severe disease by the end of the summer. The plants are weakened by the fungi, will have fewer leaves, roots, and crowns. The result is fewer strawberries next spring.

Renovation reduces problems with fungal leaf spot diseases in several ways. The first step is to mow and remove the clippings. By removing the infected leaves from the patch, the fungus is no longer able to spread in this season or survive the next. The new leaves produced in August will be healthier without the infected leaves.

The fungi that causes leaf spot diseases grow well in moist conditions so we may not have as much trouble this year. During renovation rows should be narrowed and weeds removed. This allows better air circulation through the patch. As a result, leaves will dry quickly, and the fungi will have a more difficult time spreading the disease.

Leaf spot is caused by a fungus that starts out as small purple spots. As they grow, the center of the spot turns light grey or white but maintains a purplish red border. These spots remain small and circular so they earn the common name "bird's eye spot". In severe cases, several spots can grow together and kill the leaf.

In patches where leaf spot has been severe in the past, other controls may need to be considered. Moving the patch to a new location with at least six hours of sun each day may help. Drip irrigation or soaker hoses to minimize the moisture on the leaves is also a good practice. Finally, there are resistant cultivars available for leaf spot.

Leaf scorch is caused by a fungus that also starts out as a purplish spot, but the spots never develop a white center. Instead the tissue around and between the spots turn purple or red. As the infection progresses the edges of the leaves dry and turn brown, making the leaf look scorched. Depending on the susceptibility of the cultivar, a severe case of leaf scorch can reduce next years yield by 20-40 percent. Severely infected plants are also easily killed by heat, drought, or cold extremes. Resistant cultivars are also available for leaf scorch.

Leaf blight is caused by a fungus that starts a purplish red spot with a grey or tan center. These are easily confused with leaf spot. As these spots grow, they widen out into a large v-shaped lesion with a brown center of dry dead tissue edged by a purplish red v-shaped border. The leaf tissue right outside the v-shaped lesion is often yellow fading to green. The fungus that causes leaf blight can also cause a soft rot of strawberry fruit. Unfortunately no cultivars are available to be resistant to leaf blight.

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