By Valiree Green
MN DNR Forestry, Caledonia
As summer ebbs on, the office is receiving more and more calls about “sick” trees and other plants.
Before getting into specifics, it is worth noting that several issues often can assault plants (and people) before showing signs of distress. Often multiple factors are at play, and there is seldom “a smoking gun.”
For a start, let us begin with weather. The past few years had much higher than normal moisture. This excess moisture meant an increase in fungal problems for many plants. Moisture regimes also affect insect populations. Now the 2021 growing season has a drought. While the southeast was never as dry as most of the state, a D2-level drought existed for two weeks. Just like excess moisture, too little moisture also causes problems. Finally, a very early hot spell followed by a very late cold snap caused issues all season long. Many trees were leafed out and were nipped by the late frost; these trees have looked a bit sickly all summer.
So, what does this all mean? It means STRESSED trees and other woody plants. For yard trees, IF drought happens, water deeply once every 10 days or so. The key is deeply and not just the lawn sprinkler for an hour. A trickle hose works best. Do not fertilize. Also at the beginning of freezing weather, water deeply so the soil has moisture for winter. Use the same trickle hose idea. For woodland trees, a resilient forest is one with species and age-class diversity at the proper stocking level (not too densely populated). Proper management happens over the life of a forest so plan for the long term with woodland management.
Several tree health occurrences people notice are hickory death and Fall Web Worms. In some areas numerous hickory trees (both Shagbark and Bitternut) are dying. This is a result of a native insects.
Fall Web Worms get lots of attention because they are impossible to miss. They build large webbed nests on branch ends. While unsightly (and a bit creepy-looking), they pose no real threat. The population is very high along State Highway 26 south of Brownsville but they occur all over. If your yard tree has a nest that is just too bothersome, remove the webbing and put in a bucket of soapy water. Sprays are not terribly effective and often damage non-target insects.
Bur Oak Blight has been around awhile and seemingly was a minor health issue. Now with the other stresses, it has begun to kill some trees.
Lastly, leaf damage or loss this late in the growing season is insignificant. Leaves have made food all summer and are nearly finished doing that. Trees and woody plants are likely to drop leaves early this year due to the drought and heat.
For more forest health information, visit https://www.dnr.state.mn.us/fid/index.html.