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What is it?
Scab in peach and nectarine trees is a plant disease which is caused by cladosporium carpophilum. Cladosporium carpophilum is a fungus and in addition to peach and nectarine trees, cladosporium carpophilum scab attacks all of the stone fruits. Damage from scab can be severe, affecting the fruit harvest, as well as the peach or nectarine tree itself. Deformations, cracks and death are common in peach and nectarine trees infected with cladosporium carpophilum fungal scab.
What does it look like?
The first signs of fungal scab in peach and nectarine trees usually presents as small spots on the fruit. Typically these small spots are and olive green to tannish color and the spots of scab often appear about half way through the stone fruits growing cycle. Peaches and nectarines usually have spots which begin as a small cluster on the stone fruit near the steam and spread outward in an ever growing circular pattern of small olive green spots. As the cladosporium carpophilum scab infection gets more severe, the small olive spots will turn brownish. The browner they get, the more velvety the scab spots will feel to the touch. Often as the olive or brown spots continue to erupt and spread the peaches and nectarines will become dwarfed, have deformations in their growth patter, or crack and split open. Leaves of the peach and nectarine trees may also be infected with cladosporium carpophilum scab. This damage will show up as small holes in the lives, or spots and pitting on the peach and nectarine leaves and twigs. Often many of the twigs die off. In severe cases, the entire tree can die if the cladosporium carpophilum fungal scab is not treated.
How does it manifest?
Fungal spores which have over wintered on peach and nectarine plant debris such as fallen leaves and twigs, emerge. Fungal spores often over winter on fallen fruit which is known as a mummy, or mummies if there are more than one stone fruit. Fungal spores are also splashed from the lesions on the peach and nectarine tree bark. Water splashes fungal spores from these over wintered portions of infected peach and nectarine trees. Wind can also spread fungal spores. Those fungal spores which land on uninfected portions of health stone fruit trees, then begin to infect them rapidly. As cladosporium carpophilum scab infection continues on previouslu uninfected leaves, twigs and stone fruits the entire tree may quickly become reinfected and show signs of damage due to the spread of fungal spores which over wintered and spread each spring. This is why it is especially important to treat signs of cladosporium carpophilum scab as soon as they are evident as peach or nectarine tree damage and not let the damage continue the following year’s growing season.
What can you do about it?
Once spots appear, you have no choice but to ride out the rest of the season. Stone fruits which have spots but have not cracked can be eaten if peeled. Although they may look unsightly, they are still edible. Those peach and nectarine fruits which have cracks should be discarded because they have been open to additional fungal or bacterial infections. At the end of the harvest be sure to clear up all fallen fruits and plant debris so that the cladosporium carpophilum fungus cannot over winter on them. The following year as soon as the petals have fallen from the peach and nectarine trees, you will want to spray the stone fruit trees with chlorothalonil containing fungicide. Captan is an alternative choice that also works well. You may need to re-spray at ten day intervals if cladosporium carpophilum scab is particularly troublesome in your region. You can contibue applying captan or chlorothalonil to your stone fruit trees up until about 30 days before the peach and nectarine harvest.
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