Let’s review two important fall fruit tree tasks. There is a common disease of stone-fruit trees and a common pest of apple and pear trees, and both need preventive treatment at this time of year.
Coryneum blight on stone fruit trees
If you have a stone fruit tree, and you’ve seen holes in the leaves, or raised, rough spots on the fruits this summer, your tree may have been infected with Coryneum blight, a fungal disease that can infect stone fruit trees and their ornamental relatives. It is most common on peaches and apricots. Coryneum blight causes necrotic spots on the leaves that dry and drop out, leaving holes. Infected buds die, and twigs can be girdled and killed when that happens. Infection on the fruits can look like crusty freckles or bumps. The fruit is still safe to eat.
There are a few things you’ll need to do for your tree to reduce or prevent this problem next year.
- Take steps to prevent sprinklers from hitting the canopy of the tree.
- Prune out dead twigs, twigs with dead buds and twigs with dark, sunken bark and dispose of them.
- In the fall, spray the tree with a fungicide that contains the active ingredient chlorothalonil when 50% of the leaves have dropped from the tree.
- Clean up thoroughly under the tree once all the leaves have dropped.
- In the spring, spray the tree again with chlorothalonil a few days after the petals drop from the blossoms.
Bister mites on apple and pear trees
If you have an apple tree with brown spots on the leaves or pear leaves with lots of small dark brown or black spots on the leaves, your tree may be hosting blister mites. Blister mites are members of a large group of mites called Eriophyid mites. These tiny mites, much smaller than spider mites, can only be seen with a microscope or good hand lens, but their damage is easy to see on pear leaves. The damage is usually only cosmetic, but a very severe infestation can reduce photosynthesis for the tree.
Blister mites overwinter under the leaf bud scales on trees. In the early spring when days are mild and leaf buds begin to open the mites move onto the underside of leaves, and into the leaves where their feeding causes blisters. The mites remain inside the blisters feeding and reproducing for the rest of the growing season.
The blisters are light green to yellow early in the season and gradually darken. By mid-summer the blisters are brown on apple leaves and very dark brown or black on pear leaves. Infested leaves usually drop earlier than healthy leaves, but before the leaves drop, blister mites will exit the leaves and move back onto the tree and under new bud scales.
Since light to moderate infestations don’t affect the health of fruit trees, many home fruit growers choose to ignore blister mite damage. If your trees have had a heavy infestation, you can consider applying some kind of control.
Summertime sprays aren’t effective for controlling blister mites because the mites are protected inside the blisters, but we’re approaching the time of year when spraying the trees will make a difference. Apply a single spray of carbaryl, sulfur, neem oil or horticultural oil after fruit harvest but before the leaves drop. You can combine carbaryl and oil, but you shouldn’t combine sulfur and oil. in the spring, whether your tree had a light infestation or a heavy infestation, apply a delayed dormant oil spray when the leaf buds begin to swell.