OTTUMWA —
Forestry officials in Iowa have been seeing an increase in tree diseases for several years. This summer’s storms and dramatic weather have only magnified those problems.
Tivon Feeley, forest health specialist with the Iowa Department of Natural Resources, came through southern Iowa two weeks ago to see what conditions were like. He says he has seen quite a decline in the area’s tree health.
“There’s so much going on in the forestry world right now, and the drought doesn’t help,” Feeley said. The storms that came through made a wound that’s letting in infection and pests. It’s just been a tough year.”
Cases of bur oak blight, oak wilt and Dutch elm disease, along with a variety of other diseases, were all visible and abundant.
Ray Lehn with Iowa State University Forestry Extension says there is a great concern in southern Iowa about the health of trees.
“I get about 20 calls a week about dead trees,” he said. “A lot of it is what they’re calling environmental stress. The tough weather, combined with the early wet weather, puts stress on the trees. Then the secondary disease and insects come in and kill them.”
Bur oak blight
While bur oak blight has been recognized in several states since the 1990s, it was first reported in Iowa just seven years ago. Researchers in Iowa confirmed that this disease is caused by a new, and yet unnamed, species of Tubakia. There are now five known species of Tubakia that can infect bur oak in Iowa, but only one species causes the dramatic leaf symptoms and tree mortality characteristic of this blight.
“This is fairly new here, we just don’t know why,” Feeley said.
a tree, the leaves will turn brown along the veins. As the leaves turn completely brown, they fall off. The disease tends to affect the entire tree, working from the bottom of the tree up.
As opposed to many other types of tree infections, bur oak blight is treatable. Professionals will inject a chemical called Alamo into the base of the tree.
“We don’t know how long (the treatment) will last, but it’s a slow-moving infection, so that is to our benefit,” Feeley said.
Oak wilt
Oak wilt is an aggressive fungal disease, killing thousands of oak trees in forests, wooded lots and home landscapes. The symptoms include wilting and discoloration of the foliage, premature leaf drop and rapid death of the tree within days or weeks. Trees become infected with oak wilt either by passing infection between root systems of adjacent trees or through insects, commonly the picnic beetle, that carry the fungus to other trees that have been wounded.
Iowa began to see oak wilt aggressively 5-10 years ago, particularly in red oaks and pin oaks.
“Oak wilt is fatal, and the tree will die very quickly,” Feeley explained.
The best tactic in preserving trees and preventing wilt is to treat healthy trees with Alamo, the same chemical used to fight bur oak blight.
Dutch elm disease
Introduced to the United States in the 1930s, Dutch elm disease is still one of the most destructive shade tree diseases. It kills individual branches and eventually the entire tree after just a few years of infection.
Infected leaves wilt and turn yellow first, then brown. This will usually happen in the spring shortly after the leaves first appear.
Elm bark beetles use wounded trees to reproduce, and the disease they carry is spread as the insects move from tree to tree. Once infected, the tree can spread the disease through its root system to nearby healthy trees.
Pruning and insecticides may be used if the disease is caught early enough, before 10 percent of the tree is affected. After that, elms with major amounts of the disease will die and need to removed before spreading the disease to other trees.
Finding answers
The best way to determine the cause and extent of tree diseases, Feeley says, is to have a professional assess each individual situation. The Plant and Insect Diagnostic Clinic at Iowa State University provides diagnosis of plant problems including plant diseases, insect damage and assessment of herbicide damage. They also help with the identification of insects and weeds from the field, garden and home.
Iowans can send in a sample of their diseased tree and have it tested to find out the specific problem and treatment option, if one is available. This may take a few weeks, depending on the tree species.
“But there’s always hope. Most of these diseases are treatable, and you can always replant and diversify,” Feeley said.
And diversification of the trees in an area can be a simple tool to prevent the spreading of fatal forestry diseases.
“You want no more than 10 percent of one species in the area. That’s what you see in the native forest,” he said. “That way, if disease moves in, you won’t lose everything all at once. When it’s more dense, disease moves through more quickly.”
Diagnostic clinic at ISU
To contact the plant and insect diagnostic clinic at Iowa State University, call 515-294-0581 or go online to www.ent.iastate.edu/pidc
CNHI/Southeast Iowa
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While some trees in southern Iowa are doing fine, others are struggling this season due to a variety of factors. Mark Newman/The Courier
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