Peach Pests III: Diseases of Fruit 

 and Foliage 



Karen I. Hauschild 



University of Massachusetts Cooperative Extension System 



In "Peach Pests I" and "II," I discussed insect 

 and mite pests of peach finiit, foUage, and wood. 

 In this article I will focus on the diseases of peach 

 fiiiit and foUage. 



There are several frequently observed dis- 

 ease problems of peach fruit in Massachusetts. 

 The most common of these is brown rot; how- 

 ever, peach scab and bacterial spot also can be 

 troublesome. X-disease and peach leaf curl are 

 the most frequently encountered foliar disease 

 problems. 



Below is a brief description of each of these 

 problems and basic information on non-chemi- 

 cal control measures. 



Brown Rot 



Brown rot of peaches is caused primarily by 

 Monilia fructicola (Wint. ) [There is another spe- 

 cies oiMonilia, M. laxa (Aderh. & Rhul.) which 

 normally is associated with almond, apricot, or 

 tart cherry.] M. fructicola is a fungus that over- 

 winters in mummified fruit, or in infected flow- 

 ers or twigs. As frviit buds open in the spring, 

 smaU apothecia (cup-shaped mushroom-like 

 fruiting bodies) develop from mummied fruit. 

 Development is favored by adequate moistin*e 

 and temperatures between 63 and 68°F. Within 

 each apothecium, asci bearing 8 ascospores each 

 are produced. When moisture hits these asci, the 

 ascospores are ejected and carried by wind to 

 peach blossoms where they cause infections. 

 The most susceptible flower part is the pistil. 



Brown rot infections also can occur when 

 conidia arise either from cankers on the tree or 

 from the surface of fruit mummies. Spores from 

 these conidia are carried by wind or rain to 

 susceptible peach flowers. (For conidia to form, 

 relative humidity must be 85% or higher.) In- 

 fected blossoms brown and wither but remain 



attached to twigs. 



During summer months, brown rot activity 

 decreases, but increases again as fruit begins to 

 mature. Conidia produced on infected blossoms 

 or on green fruit usually are the source of infec- 

 tion for fruit at harvest. Fruit infection can occvir 

 directly through the fruit cuticle, through natu- 

 ral openings on the fruit, or, most readily, 

 through wounds. Warm, wet weather favors 

 brown rot infections. Under optimum conditions 

 for the fungus, mature fruit can decay in a 

 matter of hours. Initial infections on fruit ap- 

 pear as brown, dry blotches that spread rapidly 

 over the finiit. Spores are produced 6x)m these 

 blotches, resulting in grey fiizz. Handling in- 

 fected fruit also can spread the disease to 

 uninfected fruits. 



Removing infected and mummified firuits 

 can reduce disease inoculum levels. Mowing in 

 late fall also helps reduce inoculum. Removal of 

 twigs infected with blossom blight helps control 

 future brown rot infections. Fungicides apphed 

 at bloom and before moistiire forms on the 

 surface of maturing fruits help prevent brown 

 rot infections. 



Peach Scab 



Peach scab is an occasional problem locally, 

 but is more prevalent in warmer peach growing 

 areas than here. Peach scab is caused by a 

 fungus, Cladosporium carpophilum, that over- 

 winters on twig lesions. Conidia are produced 

 from these lesions in the spring and they infect 

 peach fi-uit a few weeks after petal fall. Forty to 

 70 days after an infection has occurred small, 

 greenish circular spots appear on fruit surfaces, 

 especially near the stem end. As lesions age, 

 they become velvety (like apple scab) and black. 

 If infections are severe, the lesions coalesce. 



Fruit Notes, Winter, 1993 



