One of the most noticeable diseases on peach and oak trees is caused by fungi in the Taphrina genus. We talked about these fungi early in the season in issue No. 4. Leaves on affected plants become blistered, malformed, thickened, and often reddish in color. Affected leaves drop from the trees, giving the tree a very thin canopy, even though surrounding trees look healthy. The disease is particularly damaging to peach fruit. A simple control measure is to spray a fungicide on trees that have this problem. The spray must be applied when the tree is dormant--before the problem occurs. There is no rescue treatment during the growing season. The idea is to kill the fungus as it overwinters on the twigs and bud scales. Thorough coverage is essential.
This year, several homeowners complained that sprays had not prevented this disease. I have not found any information indicating that the fungicides are failing in other locations or that the fungus has developed resistance to the fungicides. It is likely that the chemicals used did not adequately cover the entire tree or that they were not agitated during the spray process. Some chemical options registered for peach leaf curl include Spectro by Cleary, bordeaux mix, copper fungicides, lime-sulfur, and sulfur. Many of these chemicals, especially bordeaux, are difficult to keep mixed, and sprayers often become clogged with chemicals. Cool temperatures only increase mixing problems. Because trees should be sprayed only when they are dormant (when they have dropped leaves and are no longer actively growing), we suggest spraying now.This may help if you forget to spray in February or early March before buds swell and begin to grow.