Water your drought-stressed oaks
Last August, the leaves on many oaks in Itasca, Aitkin, Cass, and Beltrami Counties started wilting because they were being attacked by the two-lined chestnut borer. These oaks were stressed by forest tent caterpillar defoliation in 2001 and 2002 and the lack of rain in the spring of 2002. Adult two-lined chestnut borers are attracted to stressed trees where they lay eggs in bark fissures. The larvae that hatch from these eggs feed beneath the bark in meandering galleries that cut off the water conducting vessels, causing leaves to wilt and the tree to die. During May and June of 2003, adult borers will be emerging from these trees and they will be looking for more stressed oaks to attack.
The population of adult two-lined chestnut borers will be much higher this year than it was last year. Many parts of the state continue to be dry. Some parts of the state will still be experiencing forest tent caterpillar defoliation. The combination of drought and defoliation is likely to result in a lot more dead oaks this year.
The best thing you can do for your stressed oaks right now is water them. Trees should receive at least 1 inch of water per week during the growing . If they don't get this from rainfall, then help them out by watering. Also protect your oak trees from defoliation this year, if possible. Additional information about two-lined chestnut borer can be found on the DNR Forestry web page.