Even healthy strawberries have issues [UPDATED]Published 7:04am Monday, July 2, 2012 Updated 12:06pm Monday, July 2, 2012
It’s been a good year for strawberries. Now that you have picked all your June berries, it’s time to get back down on your knees and look for trouble. There are three diseases to look for: strawberry leaf spot, leaf scorch and leaf blight. They all survive in our winters in the mature perennial leaves of the strawberry plant or in leaf debris in the strawberry patch. All three are fungal diseases and can infect both wild and cultivated berries. It can be a minor problem if there are only a few spots or a major yield reducer if the fungus is allowed to spread uncontrolled.
Spores of the fungi are spread by splashing water, or by wind. This starts the infection on new leaves early in the spring. Although it may seem like a minor infection at the time, the fungi will continue to grow and spread all season long whenever the weather conditions are favorable. Think rainy, windy days. Overhead watering can increase the moisture on the strawberry leaves resulting in increased problems. The berry plants, weakened by this fungi will have fewer leaves, root and crowns resulting in a poor crop next year.
You need to know what to look for. Strawberry leaf spot starts out as small purple spots. As they grow, the center of spot turns light gray or white but still has a purplish border. The spots can grow together and kill the leaf. Leaf scorch starts out the same way but never develops the white center. Instead the tissue around and between the spots turn purple or red. The next step is for the edges of the leaves to turn brown making the leaf look as if it has been scorched. A severe infection of this fungi will reduce the yield from 20 to 40 percent. The plants are also easily killed by heat, drought or very cold weather.
Leaf blight also starts out as a purplish red spot with a gray or tan center. As these spots grow, they widen out into a large V shaped lesion with a brown center of dry, dead tissue edged with a purplish/red V shaped border. This fungi can also cause a soft rot of the strawberry. All three fungi can infect the leaf stem, the stem that connects the mother plant to the daughter plant and the fruit.
The good news is that renovation of the patch can significantly reduce fungal problems.
First, mow the patch using a bagging mower. The object is to remove diseased leaves. If there are weeds or grass between the rows, mow them too. Next, till the patch. You want to have narrow rows, only 9 to 12 inches wide. This allows better air circulation through the berries. Usually the older plants produce smaller and fewer berries so you really aren’t losing much production. Then fertilize. It is a good idea to have your soil tested before this step to determine what kind and how much fertilizer to apply.
There is nothing like another chore that must be done in the summer.
Bev Johnson is a master gardener with Otter Tail County.