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Figure 1. Peach Scab. |
SYMPTOMSPeach scab is caused by the fungus Cladosporium carpophilum and
occurs on peaches, nectarines, apricots, and plums. The disease can
affect twigs and leaf petioles, but the most serious damage results from
fruit infection. Twig cankers begin as small, reddish lesions on current
season's growth. These cankers expand slowly and may not be visible
until mid-summer. The small cankers have irregular margins, but do not
cause sunken areas on the bark. Fruit lesions start as small greenish
spots. These generally don't appear until the fruit is half grown even
though infection occurred earlier in the season. Older lesions are
approximately 1/4 inch in diameter and develop a dusty or velvety green
appearance. The numerous lesions typically are clustered near the stem
end of the fruit. Extensive spotting can result in fruit cracks, which
serve as entrance points for several fruit-rotting fungi. DISEASE CYCLEThe fungus overwinters in lesions on twigs. Conidia are produced in
the spring after petal-fall and are windblown or splashed about by rain.
The conditions which favor disease development are temperatures above 60
F for spore production, over 50 F
(optimal 72 F to 86 F)
for spore germination, and between 36 F
and 95 F for disease development.
Most infection occurs at the shuck-split stage of growth, although the
fruit remains susceptible through harvest. CONTROLMost scab infection occurs between shuck-split and 6 weeks after shuck split. This period coincides with the peak spore production by the fungus. During this time, fruit should be protected with regular fungicide applications. Consult the Commercial or Home Fruit Spray Schedule for the types and rates of fungicides that are effective in controlling scab. Fungicide sprays during bloom and petal fall are not necessary for scab control. Proper pruning increases air movement within the tree crown and decreases the likelihood of twig infection. |
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Web updated 9/01/06 |