Introduction: Peach scab is caused by a fungus which can be extremely damaging to
trees throughout the mid-Atlantic region because of the typically warm, wet weather during
the day through the mid-season period. The disease appears to affect all cultivars of
peach and is known to occur on nectarines and apricots as well.
II. Symptoms: The most notable symptoms of peach
scab occur on the fruit, where small, greenish, circular spots gradually enlarge and
deepen in color to black as spore production begins (photo 2-60). Fruit lesions are most
common on the shoulders of the fruit, but can occur anywhere on the surface. Where
numerous, they often coalesce and may lead to cracking of the skin as the fruit enlarges,
allowing rot organisms to enter. The overwintering twig lesions (photo 2-61) are clearly
visible during the early season as small, grayish, more or less circular, slightly sunken
lesions on the previous season's shoot growth.
III. Disease Cycle: The pathogen
overwinters in small twig lesions on last season's shoots. Conidiospores, produced in
these cankers during the early spring, are splashed by rain to young fruits and new shoot
growth. Rain is required for infection and a very long incubation of 40 to 70 days is
needed for symptom development. Although the fruits remain susceptible through harvest, it
is usually only infections that occur during the shuck split to pit hardening stage of
development that have an opportunity to show symptoms before harvest. Twig infections that
result in the formation of small overwintering lesions can occur throughout the season.
Secondary infections may occur on twigs but usually do not appear on fruit, except on late
IV. Monitoring: Monitoring for peach scab begins
with an awareness of where there was a problem the previous year. Be observant for
overwintering twig lesions (photo 2-61) while pruning, record their presence on sample
trees, and mark several locations to monitor for sporulation activity later. The critical
time for effective disease control begins at the shuck split stage of fruit development.
By the time the disease appears, it is too late to do anything about it during the current
Beginning in mid to late season, monitor 25 fruit on each
sample tree for lesions (photo 2-60) which are most common on the shoulders of the fruit,
but can occur anywhere on the surface. Where numerous, they often coalesce and may lead to
cracking of the skin as the fruit enlarges, allowing rot organisms to enter. A total of
ten to 20 fruit infections and greater than 20 fruit infections represents moderate and
high risk, respectively. These damage levels indicate that improvements in disease
management are needed.
V. Management: Proper and regular
pruning facilitates air movement, reduces length of wet periods, and improves spray
penetration into trees. Fungicide sprays, applied at 10- to 14-day intervals, should
be made beginning at petal fall and continuing until 40 days before harvest.
Chemical control -
Chemical control - home
orchardists (pdf file - Acrobat Reader required)
Text prepared by P. W. Steiner and K. S.
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