Oak wilt has gotten a lot of press recently, as it should, because this devastating disease can kill a tree in the span of a month or less. The conservation district has received several calls lately about oaks that look unhealthy, and upon inspection, it turns out that in several of these cases, the cause has been another malady known as oak decline, and not oak wilt. The late frosts of recent springs are probably forgotten, it’s been many years since there was a major gypsy moth outbreak, and as we all know the drought is over. Yet these stress agents of the past combine to create the condition foresters call oak decline
Oak decline is a condition and not a disease. Drought, insect defoliation and frost injury are considered to be the major factors leading to decline. These factors weaken the trees, and then a root disease or an insect can attack the tree and propel it to the final stage where the tree dies.
Trees suffering from oak decline progressively die back from the ends of the branches with the remaining part of the tree having sparse foliage. The individual leaves look healthy but the overall tree looks very unhealthy.
In contrast, trees that suffer from oak wilt have leaves that are green at the base and brown at the tips over the entire crown. These leaves will drop rapidly in the middle of the summer, and the entire tree will die in a matter of a few weeks.
A trained professional forester can help properly diagnose which one is present, and in fact, both may be present. Oak wilt is contagious disease that can cost the landowner a lot of money to control. Oak decline can kill trees but may not require the same level of intervention and cost.
Every spring we hear of the danger of late frosts to the fruit tree crops of western Michigan. We don’t realize that even though forest trees will eventually produce a crop of leaves, having to “re-leaf” after a late frost causes the tree to suffer from depleted food stores in the roots. In the sandy, low fertility soils of central Northern Michigan, recovery from such food storage depletion is slow to oftentimes non-existent.
Many who have lived in this area for years will remember the devastation of the gypsy moth to the forests of the Cadillac area. Having to re-foliate year after year stressed many of the trees of our forests. The gypsy moth may be gone, but its effects on the forests are part of the accumulated stress on oak trees.
We often don’t realize how dry spells and droughts affect the forests of our area. Obviously young trees and seedlings with their shallow root systems have struggled to survive the hot and dry summers of the past two years. What is less than obvious is the effects of this dry weather on older, more established forests. Rains of less than inch may help your lawn grass grow but small amounts of rain do little to alleviate dry conditions in the deep rooting zone of mature trees. Hardwood trees, such as oaks, often have a delayed and accumulating effect of prolonged dry weather even years after the rains have returned.
Red vs. White Oaks
To many people an oak tree is an oak tree. However, oaks can be divided into two broad groups: red oaks and white oaks. Red oak leaves have pointed tips, while white oak leaves have rounded lobes. Oak wilt affects trees in the red oak group almost exclusively. Oak decline affects all oaks, but where it is found tends to follow the quality of the soil. Oaks growing on dry, barren soils are most susceptible. In our area, it has been observed primarily on northern pin oak, which is a member of the red oak group.
The course of action is very different for oak wilt and oak decline. Having a trained forester identity the problem is crucial and can save the property owner much grief and money. A forester can also provide management recommendations based on the specific conditions at a given site.
Larry Czelusta is the Conservation District Forester serving Wexford and Missaukee Counties. For more information on managing your oak trees, you can call him at (231) 775-7681, ext. 3, stop by the office located at 7192 E. 34 Road in Cadillac, or email him at firstname.lastname@example.org