Scab of almond and stone fruits—Cladosporium carpophilum =Fusicladium carpophilum
This scab fungus infects the fruit skin or nut hull, leaves, and young shoots of almond, nectarine, and peach.
Identification
On leaves and new shoots symptoms first appear as yellowish blotches or water-soaked spots. These spots turn grayish when spores are produced and have a greasy or oily appearance.
Small, grayish black spots develop on nut hulls or stone fruit skins, most commonly on the upper surface. The spots may grow together to form large, dark blotches. When numerous lesions coalesce on fruit, cracking may occur as the fruit enlarge. Lesions may have green or yellow halos after fruit begin to color.
Life cycle
The fungus that causes scab overwinters as mycelia in lesions on first-year twigs. Spores are produced in these lesions when humidity exceeds 70% beginning during bloom and continuing for several weeks. The spores are spread by air movement and splashing water. They can infect developing fruit and nuts, new shoots, and young or mature leaves. It is generally several weeks after infection before scab damage appears on the fruit or nuts.
Damage
Important damage occurs on fruit and nuts. Scabby spots on the skin make fruit unappetizing. If scab is abundant and uncontrolled for several seasons in a row, the trees can be weakened and their yield amount decreased.
The disease has historically been important in California only on almonds. However after springs with higher than average rainfall, the disease can also be important on peach and nectarine.
Solutions
Use drip irrigation where feasible. Avoid overhead sprinklers or aim them at a low angle or shield them to avoid wetting foliage.
Prune off some interior limbs and train young trees to allow good penetration of sunlight and air movement in the canopy, which can help to reduce the abundance of scab.
On trees where scab has been a problem they can be thoroughly sprayed with chlorothalonil or thiophanate methyl within 3 weeks of full bloom and again at 5 weeks if disease was severe the previous growing season. Note that if fungicide is applied during bloom or at petal fall as is commonly done to control for brown rot or at petal fall for shot hole, this also reduces the subsequent abundance of scab.
Adapted from Integrated Pest Management for Stone Fruits, Pest Management Guidelines: Almond, and Pest Management Guidelines: Peach, University of California Statewide Integrated Pest Management Program (UC IPM). |
Scab on leaves first appears as small, yellowish blotches or water-soaked spots.
Older scab lesions on leaves develop dark spores that have a greasy or oily appearance.
Dark lesions of scab on the skin of a peach.
Hulls of almond with abundant dark lesions that have merged to form large blotches.
Scab overwinters in bark lesions on young shoots.
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