Plant Pathology Infobytes April 21, 1998 How to Keep Your Apple Trees from Rusting Most apple varieties grown by Mississippi orchardists are susceptible to cedar-apple rust and are annually attacked by this fungus disease. In seasons when cedar-apple rust is severe, leaves on many apples trees turn a rusty orange color because of the disease and fall from trees. While cedar-apple rust doesn't kill trees, the repeated effects of leaf destruction and defoliation eventually leads to weakened trees and poor apple yields. Weak trees are more susceptible to other problems, such as winter injury, which frequently lead to tree death. The fungus which causes cedar-apple rust overwinters on cedar trees. In fact the overwintering site of this fungus is very conspicuous on cedar trees across the state at this time of year as orange, globular-shaped structures about the size of tennis balls. This stage of cedar-apple rust has been particularly noticeable this spring because of recent periods of rainy weather. These orange balls (technically referred to as "telial horns") are the source of fungus spores which are blown to apples where young leaves become infected during periods of wet weather. As the disease progresses, apple leaves turn the characteristic rusty orange color. What should you do to protect your apple trees from cedar-apple rust? Fungicide applications with a fungicide such as mancozeb (sold under several trade names at farm and garden supply stores) should be applied to apple leaves. When applied according to label directions, this fungicide will help reduce further infection of your apple trees by the cedar- apple rust fungus. Captan is not recommended for cedar-apple rust, since this fungicide has no effect on the disease. As an interesting point, while cedar-apple rust can severely injure apple trees, the disease has little, if any, injurious effect on cedar trees. Give us a call at the County Extension Office if you have questions about developing a disease management program for your orchard.

Written by the late Dr. Frank Killebrew Visit: DAFVM || USDA Search our Site || Need more information about this subject? Last Modified: Thursday, 05-Oct-06 08:37:22 URL: http://msucares.com/newsletters/pests/infobytes/19980421.htm Mississippi State University is an equal opportunity institution. Recommendations on this web site do not endorse any commercial products or trade names.