Stress buildup killing Kansas trees
Trees in many areas of Kansas have died suddenly this year. In some cases, the trees leafed out before dying. In others, the trees simply never leafed out when the growing season began.
"We've also been getting reports about living trees that have lost whole branches. Additional live trees have leafed out but then lost leaves in a kind of general thinning," said Ward Upham, horticulturist with Kansas State University Research and Extension.
The cause isn't proving to be some invading insect, virulent disease or unusually fierce weather event.
"Although the trees seem to be dying quickly, they appear to be reacting to a gradual accumulation of weather-related stresses. The causes probably stretch back at least as far as spring 2008," Upham said.
The samples and reports coming into K-State this year from both individuals and county/district Extension offices suggest the particular causes and plant responses can vary widely--even among trees in the same town. So, owners will need to assess their own situation before deciding what to do next.
The stressors may range from last year's super-saturated soils in some areas to winter's dry weather and April's abrupt cold snap, Upham said. Trees' specific reactions also can provide insights.
"For example, trees that seemingly withered overnight may actually have died some time earlier. They simply had enough food stored in reserve to put out leaves and perhaps even to grow for a while. As soon as they used up that food, however, they abruptly began to look as dead as they really were," he said.
One problem with identifying this kind of reaction is: The symptoms can look almost the same as those caused by another problem. The May beetles that attack from April through June not only feed at night but also work to strip the leaves from plants. If enough beetles are growing and feeding in the same place, the bared trees they leave behind can look defunct.
(May beetles are one of the two kinds of adult insects who start out life as the white, soil-dwelling, C-shaped grubs that cause so much damage to lawns.)
"Fortunately, healthy trees recover fairly easily from May beetle damage. They just throw out a new set of leaves. But, that's one reason why you always should check twigs before cutting down a tree that simply looks dead," Upham said.
Dead trees have dry, brittle stems that snap when broken, he explained. Live stems may break, but they aren't brittle or dry. So, they just need time to put out a new set of leaves.
For trees in which individual branches have died, Upham recommends cutting out the deadwood.
"Several problems--including verticillium wilt disease--can cause this same kind of loss, though," he said. "So, if you suspect some factor other than stress is at fault, you may want to take a sample of the cut branch to your nearest county or district K-State Research and Extension office. For a small fee, that office can send your sample for testing in our diagnostic labs on campus."
Fortunately, trees usually recover from losing leaves when they look as if a barber has reduced their "hair" volume with thinning shears, Upham said. With leaf loss this early in the growing season, they have ample time to replace those leaves and then make and store the energy they need before winter.
"You should, of course, do what you can to keep their stress level down from now on," Upham said. "For example, if they're not getting enough rain for good growth, slowly irrigate the area under their canopy every few weeks or so through the growing season--if possible, getting moisture 12 to 18 inches deep.
"If they're less than three years old, however, or they're heading into actual heat or drought stress, you may want to water your vulnerable trees about once a week. Drought stress, in particular, can not only injure trees but also leave them wide open for all kinds of disease and insect problems."