Common Iowa Tree Diseases: Identification and Treatment

Trees in the Cedar Valley face threats that can weaken them and eventually kill them if left untreated. The key to saving a tree is catching the problem early. Once a disease has progressed to the point where a tree is dropping large branches or showing widespread dieback, treatment options are limited and removal is often the only practical choice. Knowing what to look for and when to call for help can mean the difference between a tree that recovers and one that comes down. Here are the most common tree diseases and pests we see in Cedar Falls and what to do about them.

Dutch elm disease has been killing American elm trees in Iowa for decades, and it is still active today. The fungus spreads through root grafts between neighboring trees and by elm bark beetles that carry the spores from tree to tree. The first sign is wilting leaves and yellowing in the upper canopy during summer. The symptoms start in one branch and spread through the tree as the fungus moves through the vascular system. There is no cure for an infected tree. The only option is prompt removal to prevent the disease from spreading to nearby elms through root grafts. If you are planting a new elm, choose a resistant variety like Princeton or Valley Forge. They are not immune, but they have much better odds of surviving.

Emerald ash borer has killed tens of millions of ash trees across the Midwest since it arrived in the United States. In Iowa, the damage has been devastating. The adult beetles lay eggs in the bark, and the larvae tunnel under the bark and feed on the vascular tissue, cutting off the flow of water and nutrients. The tree dies within a few years of infestation. Look for thinning in the upper canopy, D-shaped exit holes in the bark, and woodpecker activity that strips patches of bark off the tree. If you have a healthy ash tree that you want to save, treatment with systemic insecticides can be effective. The treatment needs to be applied on a regular schedule and is most effective when started early. Once more than 30 percent of the canopy is damaged, treatment is unlikely to save the tree.

Oak wilt is a fungal disease that affects all species of oak but is most deadly in red oaks, which can die within a single season. The fungus spreads through root grafts connecting nearby oaks and through sap beetles that carry spores from infected trees to fresh wounds. The symptom to watch for is leaves turning brown from the edges inward in the upper canopy during summer, often in a pattern that spreads from one branch to the entire tree. The most important prevention step is to never prune oaks during the growing season. In Iowa, that means pruning oaks only between November and March. Any wound during the active season is an invitation for beetles to introduce the fungus. If oak wilt is confirmed in a tree, the roots need to be cut to prevent spread to neighboring oaks.

Apple scab is more of a nuisance than a killer, but it makes trees look terrible. It affects crabapple and apple trees, causing leaves to develop olive-green spots that turn brown and cause premature leaf drop. By late summer, an infected tree can be nearly bare while surrounding trees are still full and green. The tree usually survives, but it is weakened and looks awful for the rest of the season. The best approach is prevention. Plant resistant crabapple varieties, which are widely available. If you have a susceptible tree, fungicide sprays applied in early spring when the leaves are emerging can reduce the severity of the infection. Raking and disposing of fallen leaves also reduces the spore load for the next year.

If you have a tree on your property that does not look right, do not wait to have it checked. Some problems, like emerald ash borer and Dutch elm disease, are much easier to treat when caught early. Others, like oak wilt, require immediate action to protect surrounding trees. We provide tree services across Cedar Falls and the Cedar Valley, including disease diagnosis, treatment, and removal when necessary. Give us a call and we will take a look at your tree and tell you what is going on.