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Leaf scorch appearing on trees and shrubs, despite moisture supKansas Signs of leaf scorch are showing up on some trees and shrubs across the central United States. The damaged leaves are symptoms of an internal plant problem, not an insect or disease. "We usually associate leaf scorch with drought, but it can develop any time leaves are losing moisture more quickly than their roots can replace it. This year, one likely cause is the heavy rains many areas got this spring," said Ward Upham, horticulturist, Kansas State University Research and Extension. Often, the heavy rains not only recharged the soil's moisture supplies but also temporarily drove the oxygen from that soil, Upham explained. That's probably happening again now in southeast Kansas. Being oxygen-deprived can soon damage tree and shrub roots. So, where that occurred months ago, the still-recovering roots are having trouble, keeping up with their leaves' summer water needs. Shallow soils also can cause leaf scorch or make woody plants more susceptible to the condition, Upham said. Trees growing in the soil over a layer of hardpan or rock, for example, may have a root system that's so limited it can't absorb all the needed moisture unless it gets frequent, regular watering. "Of course, root damage and poor water uptake also can be due to disease, insects, poor drainage or construction," the horticulturist said. "Plus, hot, dry winds can speed up the rate of leaf moisture loss." Scorched leaves turn brown or sometimes black, working in from the edges or tip and between the major veins. The scorching may show up over the entire plant or one side. If the condition is severe, the affected leaves may drop, he said. Deciduous plants, broadleaf evergreens, and white pines are most likely to be affected. "When the problem is root damage, about all you can do is work to ensure the plant experiences no more stress--at least through this growing season," Upham said. "When the problem's a limited root system or dry soils, you can help alleviate that by watering once a week when you don't get rain. Mulching your shrubs and small trees will then help conserve that moisture." Date: 8/28/07
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