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LET'S REDUCE THE DAMAGE TO PEACH TREES FROM CYTOSPORA CANKER 



Donald H. Peterson 

 The Pennsylvania State University 



Cytospora canker may be referred to by several different names: 

 Valsa canker, or peach canker, or just plain canker, or gummosis, 

 or perennial canker. These cankers occur on twigs, branches, and 

 scaffold limbs, in the crotch area and on the trunk, and at pruning 

 cuts. The disease occurs on all stone fruit trees, but seems to 

 cause the most concern on peaches and nectarines. During and af- 

 ter rains and periods of high humidity, gum oozes in the area of 

 the canker. When it dries, it turns black and hard. 



Smooth sections of the bark in the cankered areas become pep- 

 pered with the pimple-like fruiting bodies of the causal fungi. 

 During rainy periods, these pimples ooze a white to orange miniature 

 toothpaste-like mass of spores. These can be splashed by rain or, 

 when dry, be blown by wind. Spore production can occur anytime the 

 temperatures are above freezing. However, the disease is usually 

 not initiated when the trees are growing vigorously. Most infec- 

 tions take place during the fall, early spring, and during winter 

 when temperatures are above freezing. 



The organism causing Cytospora canker cannot penetrate healthy 

 bark or buds. It must have injured areas of some kind. The injured 

 areas most frequently entered are: (1) dead dormant buds; (2)cold- 

 injured wood; (3) pruning cuts, particularly those made when the 

 trees are dormant; (4) pruning stubs, which often die back to their 

 main branch; and (5) brown rot cankers. 



None of the stone fruit species are immune to Cytospora canker. 

 Chemical treatments alone are not very effective. Thus we need to 

 "learn to live with Cytospora canker." This can be done quite suc- 

 cessfully by your management practices. Let's begin with the new 

 orchard you are planning. 



Setting a new orchard . 



1. Your site should not be one with poor internal soil drainage. 

 Wet spots need to be drained or avoided. Trees on these sites 

 often suffer cold damage and have a considerable amount of 

 dead wood in them. The more dead wood in trees, the more like- 

 lihood of places for Cytospora to get started. 



2. New orchards should not be planted near cankered, older ones, 



and especially not downwind from them. It is nearly impossible 

 to protect the new planting from the vast number of spores com- 

 ing from the older cankered trees. Let me give you an example. 



t 



This article appeared in The Maryland Fruit Grower , Vol. 44 (No. 2) 

 1974 



