Our rainy, high humidity spring weather is ideal for the development of a number of leaf and fruit diseases. Most of these diseases can be reduced by cleaning up last year’s old leaves. The disease spores for this year’s infections are carried on last year’s old leaves. There are a number of fungicides which will also reduce or prevent diseases if applied at the correct time. Sometimes one application is all that is needed.
Roses need to be sprayed at 2 to 3 week intervals to prevent black spot, mildew and rust diseases on the leaves.
Peach and Nectarine trees need only one or two applications just as the new leaves are emerging from the buds to prevent peach leaf curl. A bad infection of peach leaf curl can reduce the fruit crop by half or more.
Weeping flowering cherries are very susceptible to shot hole fungus which attacks just as the new leaves are emerging. Two applications will largely prevent this disease.
Dogwoods and Photinia shrubs and hedges can drop a lot of leaves from a leaf spot disease. Complete leaf cleanup will largely take care of this disease. One fungicide application just as new growth starts is also very helpful.
Apple and pear scab affects both the leaves and fruit of apples and pears. Complete cleanup of old leaves will greatly reduce this disease. Biweekly fungicide applications starting with new leaf growth are necessary to completely eliminate scab. About 3 to 4 applications.
A number of fungicides are available for controlling diseases including some very effective organics. Neem oil, lime-sulfur (calcium polysulfide) and copper fungicides are three of the best organics. Daconil and Chlorothalonil are two chemical fungicides. Most effective are the systemic fungicides such as Propiconizole, Myclobutanil, and Tebuconazole. You need to check the ingredient labels to find which fungicides are included in a particular fungicide product.