Other Stone Fruit Diseases Symptoms of two bacterial diseases are becoming common. However, there's little that can be done for it at this time of year. It's reasonably effective on a preventive basis, but won't rescue a crop that's already got a serious disease problem. Apple Diseases Black rot. The frogeye leaf spot phase has been common for the last couple of weeks, particularly on Cortlands or other varieties containing mummies in the tree.
Fruit are susceptible from the time they form until harvest.
At this point in the season, fruit infections look like small, black pimple-like lesions, which won't start expanding until the fruit ripen. Ziram is a possible, but inferior, substitute for captan in blocks using summer oils. Not showing up yet, but they should be incubating right now. Continued wet weather will greatly shorten the incubation period, and provide the possibility for secondary spread once the first infections develop. Ziram's a good substitute for the captan component of a benzimidazole mix.