After wet spring, we’re likely to see diseases

When we have a spring as wet as the one we just experienced, I can pretty much guarantee that we will see diseases in the garden and landscape.

I am starting to see one in particular on crabapple and apple called frog-eye leaf spot. These purple specks are showing up on the leaves now. As they enlarge, they become more noticeable.

These spots eventually develop grayish-brown centers and form concentric rings. The rings are surrounded by purple margins or edges.

When this disease shows up on the leaves of these trees, it’s called frog eye leaf spot. When it appears on the fruit, it’s called black rot. This disease can be a major problem in apples because they are edible.

No one wants to eat a rotted apple.

In crabapples it tends to be cosmetic, unless you are growing the crabapple tree for its fruit. Believe it or not, some people do.

The variety called Dolgo has large fruits that make a great jelly.

Another apple and crabapple disease I expect to see soon is apple scab. Again, this is due to wet cool weather occurring during bud development.

Apple scab is a cosmetic problem on crabapples; however, it also affects fruits. On apples it is a real problem.

Affected crabapple leaves fall off the tree during the summer. On apples, the leaves fall and the fruits are affected by the scab, rendering them unsellable.

These diseases are somewhat tough to control. First of all, any fungicide application has to be made prior to the infection period.

Therefore, in the spring, when crabapples are leafing out, you need to be spraying the leaf surface with a fungicide that controls apple scab.

If weather conditions continue cool and damp, you may have to continue to spray into mid-June.

If you start to see the symptoms of these diseases, it’s too late to spray. If you have apple trees, you may spray a few more times to prevent any secondary infection if the weather stays cool and damp.

The challenge with applying fungicides is to find the right fungicide that works on the trees. Commercial growers adopt a regular spray program to prevent this problem.

Homeowners have a tougher time finding a good fungicide that works.

With crabapples, I generally tend to let them go on their own. I have never seen apple scab or frog eye leaf spot kill a tree. It just looks unsightly.

In both cases, apples and crabapples, look for resistant varieties when considering a tree.

There are varieties on the market that are resistant to scab and can be planted with great success. Otherwise, plan on a regular spray program to prevent both diseases. Pamela Corle-Bennett is the state master gardener volunteer coordinator and horticulture educator for Ohio State University Extension. Contact her by email at bennett.27@osu.edu.