Ornamental & Tree Diseases

Why are repeat applications of fungicides necessary? Spraying every 7 to 10 days is a lot of work. It seems that much spraying shouldn't be necessary.

Fungicides are not chemically stable. This means they break down when exposed to light, organic matter, water, and other types of environmental exposure. Also rain, especially heavy rains, wash fungicides off leaves, stems, and other plant parts. Remember also that new growth which appears will need benefit of fungicide protection. Spray intervals recommended on the fungicide label account for such factors. The label usually suggests a range of times when repeat fungicide application is needed, such as spraying every 7, 10, or 14 days. Longer intervals are used when disease severity is low, where rains or irrigation have not washed off fungicides or where weather conditions are not favorable for disease development. Some diseases are favored by cool conditions and others by warm conditions. Most diseases are favored by wet conditions and landscape plants, trees, as well as garden and orchard crops have to be sprayed more often under such conditions.