Plant Pathology Infobytes
December 17, 1996
Cedars and the Health of Your Apple Tree
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 the spring fungus spores which are produced on this host 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.
While there are additional control measures for cedar-apple rust which will need to be carried out next spring, you might want to consider a few things which could be done at this time of year as part of a control program for this troublesome disease.
Non-chemical measures this winter:
- Remove cedar trees from the vicinity of the apple orchard, preferably for a distance of a quarter mile or so. While cedar- apple rust spores can still be blown from cedars further away, the number of spores can be drastically reduced if cedars within the prescribed distance are removed.
- If cedars are part of your landscape, and you want to maintain them, prune rust galls from cedar branches during the late winter. Chemical control measures for next spring:
- Fungicides to protect apples from cedar-apple rust are needed from the prepink through the bloom stage. Applications are especially important before rainy periods. Several applications will be needed past the bloom stage to adequately protect susceptible apple tissue.
- Fungicides registered for use on apples that are effective for cedar-apple rust include various formulations of such fungicides as mancozeb. Captan is not effective for cedar-apple rust.
Give us a call at your county Extension office if you have questions about developing a disease management program for your orchard.
Infobytes newsletter was written by the late Dr. Frank Killebrew, Extension Specialist.