Peach Scab

Fruit Disease Information Note 6 (FDIN 006)
D.F. Ritchie, Plant Pathologist

Peach scab is caused by the fungus Cladosporium carpophylium which infects peaches, nectarines, and apricots.  In North Carolina, environmental conditions during the spring and early summer are usually ideal for scab development.  If no controls are used, fruit may become severely cracked, become dry and shrivel, and may not ripen. Cracks in the fruit allow for invasion by the brown rot or other fungi.

Symptoms

Even though the disease occurs on twigs and leaves, it is most often observed on the fruit.

Fruit - The first symptoms are greenish-brown to black spots approximately 1/8 inch in diameter usually concentrated near the stem end.  The lesions may be numerous over the upper fruit surface, scattered over the sides and entirely absent on the lower surface.  When infection is severe, the lesions coalesce forming a greenish-brown, velvety blotched area.  The scab lesions are superficial, but when numerous their effect prevents normal growth, resulting in misshapen and cracked fruit.
(peach scab picture)

Twigs - Twig lesions occur on current year's growth.  These lesions are light brown in color, 1/8-1/4 inch in diameter; they later enlarge and become dark brown.  The lesions are slightly raised.   They can be seen about the time that lesions are seen on the fruit but become more evident later in the season.; The lesions are superficial, thus doing little, if any, direct injury to the twigs.

Leaves - Lesions first appear on the underside of the leaf as pale green areas, usually in late summer.  On the midrib, dark brown, narrow lesions develop. If infection is severe, premature defoliation may occur.

Disease Cycle

The fungus overwinters in twig lesions.   In the spring, spores are produced on the lesion surface (primary inoculum) and are washed or splashed primarily by wind-blown rain to fruit, leaves, or new growing twigs.   On peaches, fruit are first susceptible starting 5-7 days after shuck split.   Periods of rainfall with temperatures of 65-75 F are optimal conditions for infection.  Although fruit remains susceptible until harvest, the 4-week period following start of shuck split is the most critical period for infection to occur.   The time from infection until lesions are visible may be 4-6 weeks.  Thus, infections occuring within 4 weeks of harvest do not result in visible lesions.

Control

All varieties are susceptible to scab, with some being more severely effected than others.  Generally, scab is most severe the first year the trees bear fruit (usually 3rd growing season).  This results from the large numbers of twig lesions that develop during the first two growing seasons.   Low-lying planting sites should be avoided and trees should be properly pruned to allow good air circulation, thus promoting rapid drying of fruit, twigs and leaves. Fungicides such as captan and wettable sulfur provide adequate control of this disease if applications are properly timed.  On peaches, sprays should begin about 1 week after petal-fall.  Sprays on nectarines and apricots should begin at about petal-fall.   Subsequent sprays should be applied at 10-14 day intervals until approximately 1 month before harvest.  During the month before harvest, sprays applied for brown rot control will help reduce late season scab infections on the fruit, twigs and leaves.

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Caution:  The information and recommendations in these Notes were developed for North Carolina conditions
and may not apply in other areas.

Recommendations of specific chemicals are based upon information on the manufacturer's label and performance in a limited  number of trials.  Because environmental conditions and methods of application by growers may vary widely, performance of the chemical will not always conform to the safety and pest control standards indicated by experimental data.  All recommendations for pesticide use were legal at the time of publication, but the status of registration and use patterns are subject to change by actions of state and federal regulatory agencies.  Last printed:  04/91

Published by North Carolina Cooperative Extension Service. Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.