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Issues cropping up with apricot, other fruit trees

Thu., July 18, 2013

Well, I do believe we are going to a have tomato summer this year for the first time in several years. Many people are already harvesting cucumbers and zucchini and tomatoes are setting on fast.

Aside from the successes in the garden, there are also issues showing up in the WSU Master Gardener Plant Clinic. Many of them in the last couple of weeks revolved around fruit trees.

Coryneum blight – or shot hole disease – is showing up on apricots. This disease is caused by a fungus that overwinters in infected buds on the trees. The spores from the fungus are moved around by splashing water drops from rain or overhead irrigation.

Leaves on the tree develop small, round tan to purplish spots. The tissue then dries out leaving a small hole in the leaf. The same spots form on the fruit, often accompanied by a gummy residue. Fruit can still be eaten but the damaged areas are hard to remove. The best control for this is the application of a fungicide in the fall to destroy the spore cycle before the winter rains set in.

Peach leaf curl seems quite abundant this year. This, like the coryneum blight, is caused by a fungus. The fungus overwinters in bark cracks, twigs and infected leaves on the ground and infects the buds during late winter to early spring just as the buds begin to swell.

Maximum susceptibility is between bud break and when the petals fall. The first leaves to appear on the tree will be yellowed, curled and thickened. They eventually are covered with a whitish film of spores. Twigs can be distorted and leaves will drop. Several years of repeated infection will eventually kill a tree.

The best treatment is application of a lime-sulfur spray during the late winter before the buds begin to swell. Lime sulfur can be mixed with dormant oil and then applied to the tree. Do not mix lime sulfur with any other chemical except dormant oil.

It’s cherry season and there is a good chance that some of you have found a visitor hiding in that delicious fruit. Cherry worms are the larvae of the cherry fruit fly that made the rounds of your tree just after it finished blooming.

The fly pupae overwinter in the soil and lay eggs on the newly formed fruit. The larvae then bore into the fruit, and you find it a few weeks later. There are some parasitic wasps that go after the pest but usually aren’t enough to control it.

Pheromone traps can be used to detect the fly’s presence. Once they are found in the trap, a spray containing spinosad should be applied and then again in 10 days. Spinosad is a bacterium that attacks the larvae. Apply the spray very late in the evening after the bees have gone to bed as they can carry the spray to the hive where it will attack bee larvae.

Pat Munts has gardened in Spokane Valley for more than 35 years. She can be reached at pat@

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