Fungal Growth Caused by Spring Rains
Apple scab is a common problem of both crabapple and apple trees. This spring disease results in greenish to olive spots or lesions on the leaves that soon turn yellow. They then drop from the tree, which results in a thin canopy for the rest of the summer.
Control of this disease can only be achieved as the plant is breaking bud and leafing out in the spring. Fungicides, such as chlorothalonil, can be applied on a 7 to 10 day basis from mid April through May for best results. There are also many varieties of crabapple trees available at nurseries that are resistant to this problem.
Anthracnose is another spring leaf disease of maple, ash and other species. This disease causes black to brown spots on the leaves, often appearing along the veins of the leaf. The leaf can become misshapen or distorted. Like scab, the leaves will soon drop from the tree causing more concern.
Unlike scab, K-State Research and Extension does not recommend control for this problem. It only affects a small percentage of the leaves and the plant will soon recover. To control this disease on larger shade tree, they need to be sprayed multiple times and the disease damage does not warrant the cost of the applications and the amount of chemical used.
The other spring problem that is associated with rains is a bizarre mass that develops on wood mulches in the landscape. This fungus is a pile of yellow foam, a mass that erupts through the mulch layer. It can appear almost anywhere from open areas around the plants, or even right in the middle of a plant.
This yellow fungus is often called dog vomit fungus because that is what it really looks like. Although it has an awful sounding name, it does not cause any problems. This fungal growth is a natural process of the rotting and decaying wood. The disease helps to break down the wood.
Once this growth appears there are a couple of options. First, do nothing as it will go away in time. Or run a rake through the mulch to help break up the mass and dry out the mulch. Finally, you can remove the mass and surrounding mulch and replace with new mulch.
These problems are minor and mainly cosmetic to the trees and landscape. They will soon recover.