If you have a peach tree, this may not be your year for peach ice cream. After an especially wet spring, many trees are afflicted with peach leaf curl, a fungal disease.
“It’s mostly a leaf disease, but it can also affect fruit production,” said Spencer Campbell, Plant Clinic manager at The Morton Arboretum near Lisle. “If a peach tree loses all its leaves, it may be weakened so
that it’s more susceptible to infection by other diseases.” That can lead to another reduced crop next year.
Peach leaf curl is one example of the many fungal diseases that are more common in years with frequent rainfall in spring. “Fungus spores multiply on wet surfaces,” he said. “When it rains a lot just when leaf buds are opening, the tender new leaves are especially vulnerable.”
Wet springs encourage fungus-caused diseases such as verticillium wilt in maples; anthracnose in sycamores; apple scab in flowering crab apples; rust on roses; maple leaf tar spot; and powdery mildew, which affects lilacs, phlox and many other plants. Although peach leaf curl only occurs on peach and nectarine trees, closely related diseases can affect cherries and plums.
Peaches and nectarines aren’t grown commercially in northern Illinois because most cultivated varieties are not sufficiently winter-hardy. Still, some homeowners have peach trees, especially the hardy variety
Red Haven.
In a wet year, peach leaf curl will likely cause an infected tree’s new leaves to be thickened and distorted and brightly colored in pink, red or purple. Later, as the fungus spores multiply, the leaves take on a
gray or powdery appearance until they eventually turn yellow and fall off.
Taphrina deformans, the peach leaf curl fungus, also can infect flowers, developing fruit and young shoots. “Infected flowers or fruits may fall off before you even notice them,” Campbell said.
The spores are spread to other leaves or other trees by wind or rain and will overwinter in a dormant state on the tree’s buds and twigs. If the next spring is too dry or too warm, the spores don’t get a chance to multiply and the tree may show no symptoms. But the dormant spores may still survive until a year when conditions are right.
It’s possible to control peach leaf curl with a fungicide, but the timing is important. It is best to spray in fall, after the leaves drop, or in spring before the buds begin to swell. If you think your tree has peach leaf curl, contact the Plant Clinic to confirm the identification and get advice on using fungicides. Be sure that any product you choose is labeled for fruit trees, and follow the label directions carefully.
Once you notice the symptoms of peach leaf curl in late spring or early summer, it’s too late to do anything about this year’s flowers or fruit. “At this stage, treatment won’t have any effect,” Campbell said.
For many fungal diseases, treatment is not necessary, because the diseases don’t really do much damage. “Powdery mildew and maple leaf tar spot may be unsightly in a bad year, but the plant will survive,” Campbell said.
The best way to fortify all trees and shrubs against fungal diseases is to keep them vigorous and healthy.
Water them in times when rainfall is scarce, as it often is in July and August. “Be sure to water at the base of the tree, not with a sprinkler, so you don’t get the foliage wet,” Campbell said. Avoid excessive fertilizer, which can push the tree to add too much weak new growth.
If you think a tree has peach leaf curl or any other serious fungal disease, clean up the deformed, fallen leaves, which can harbor fungus spores. Don’t put the leaves in the compost pile, where they might survive to spread the disease. Instead, put the leaves out for landscape waste pickup to get them off your property.
For tree and plant advice, contact the Plant Clinic at The Morton Arboretum (630-719-2424, mortonarb.org/plant-clinic, or plantclinic@mortonarb.org). Beth Botts is a staff writer at the Arboretum.
