Black spots on apples? It’s scab


Q. My apple tree has dots on the leaves and the fruit. Help!

Angie from Salem

A. These are the classic signs of apple scab, the most significant disease of apples and crabapples in Ohio.

This year’s wet spring and cool temperatures were the perfect mix for disease development.

The rainy and moist conditions for most of the summer kept the disease going.

Anyone who has a crabapple or an apple tree in their yard knows this disease.

Older cultivars of crabapple that bloom dark pink in spring are usually defoliated by this disease by Labor Day. While these older trees are beautiful in spring, this disease makes them unsightly in late summer. Over time, the disease weakens these trees.

Some apple trees are more susceptible than others, with the disease showing up as lesions on the leaves and on the fruit as Angie noted in her question.

The fruit is still edible, but in the most challenging years the fruit is unsightly and distorted before ripening.

For home gardeners, there are usually two main options for controlling this disease.

First is resistance. That is, in the form of choosing the right tree in the first place or by replacing a tree with one that has resistance to this fungal disease. For younger trees, replacing the tree with a resistant variety is the best option. You’ll lose a couple of years of work, but you’ll have a better tree in the long run. Links to resistant cultivars are listed below.

From an infection standpoint, all leaves and fruit from infected trees should be cleaned up and removed from the area as soon as they fall from the tree. This will prevent infection next season.

Keeping trees pruned to allow air flow and sunlight penetration into the canopy will allow leaves to dry early in the morning. This reduces infection.

In cases where trees have no resistance, fungicides are often used. There are both organic and conventional fungicides. Be sure to read the label of the product – even if it is organic – and follow the label directions. Again, the better option is to choose resistant varieties when planting.

For a list of apple trees resistant to scab and details about apple scab, visit https://ohioline.osu.edu/factsheet/plpath-fru-23.

For a list of crabapples that are resistant to apple scab, visit http://go.osu.edu/resistscab.

Eric Barrett is OSU Extension educator for agriculture and natural resources in Mahoning County. Call the office hotline at 330-533-5538 to submit your questions. Regular clinic hours are 9 a.m. to noon Mondays and Thursdays.

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