The University of Illinois Extension serves as a leader in the state for offering research-based advice on a multitude of topics. My role as a horticulture educator places me in the realm of anything that grows, creeps, crawls, or flies.
Tree fruit questions have been the most common among homeowners as of late; chiefly peach trees and more specifically peach leaf curl. As daytime temperatures rise and fruit trees begin their vigorous annual growth, peach leaf curl becomes a noticeable problem. Peach leaf curl is a fungus that can defoliate peach and nectarine trees early in the season. Symptoms include red, crinkled leaves and thick, powdery spore-covered leaves.
Unfortunately, once a home gardener sees the evidence of peach leaf curl, it is too late. The fungus overwinters on the tree, lying dormant until spring when the tree's leaf bud scales begin to open, then infecting the leaves before their emergence. As the disease progresses, the tree will drop the affected leaves and put on a second flush of healthy leaves.
Peach leaf curl will likely not kill its host, but does force the fruit tree to allocate its limited energy reserves to growing new leaves instead of peaches. Stress results from the deficit of energy in the peach tree, leaving it open to other pests and inclement weather.
Peach leaf curl is not difficult to manage. A single fungicide application in the fall after the leaves have dropped or in the spring before bud swell will control peach leaf curl. Thorough coverage of the twigs, branches and trunks are essential. Effective fungicide active ingredients include chlorothalonil, copper, and lime-sulfur. Read and follow all label directions of the fungicide selected. Pesticide misuse can lead to greater problems than peach leaf curl.
If peach leaf curl develops and trees defoliate, take steps to ensure tree health and reduce plant stress:
- Thinning fruit, especially for peach trees that have set a hefty amount, will reduce demand on the tree. Peach fruit thinning is a good practice regardless of plant stress, though it is hard for most gardeners to pick off the perfectly healthy fruit. First, remove all diseased or damaged fruit, then thin remaining peaches to about eight inches apart.
- Irrigate during dry periods. These past month has been sweltering and dry in West-Central Illinois. Gardeners will need to begin turning their attention to watering trees during weeks that we don't receive rainfall. Peach trees affected by peach leaf curl are especially sensitive to drought at this time.
- Fertilize according to soil test results. Nitrogen can help in the growth of new leaves, but don't apply nitrogen after August 1, as doing so will interfere with the trees process in preparing for winter.
- Mulch trees with shredded wood mulch, wood chips, or (best of all) commercial landscape waste compost. Mulch should be two- to four inches thick and spread as far as the tree's dripline. Mulch preserves soil moisture and regulates soil temperatures.
For more information on managing tree fruits, contact your local Extension office.