Leaf Spot Diseases


Spring rains are always great for our plants. It helps to replenish our lakes and streams and helps bring the soils back to a point of good saturation after a dry winter and before a dry, hot summer. However, when we see many days with a lot of rain and overcast skies, this can also be detrimental to our plants.

This year we are seeing a lot of fungal leaf spot diseases that look terrible on our trees. These leaf diseases are causing the leaves of many of our deciduous trees to get brown spots, turn yellow, and eventually fall off of the tree. As damaging as this looks, it is actually a minor disease and does not cause major stress to the trees. The diseases we have been seeing include anthracnose, ash rust, cedar-apple rust, apple scab, and other leaf spots.

ash anthracnose, Jason Sharman, Vitalitree, bugwood
Ash Anthracnose Photo by Jason Sharman, Vitalitree, Bugwood.org

Anthracnose is a fungal leaf spot disease that can occur on many different host trees and shrubs. There are a number of fungi that cause anthracnose and typically they are host specific. What this means is that there are a lot of different trees that are affected by anthracnose, but oak anthracnose is only found on oak trees, ash anthracnose is only found on ash trees, and so on. So, the disease won’t spread between tree species but multiple fungi may be present in a landscape.

The symptoms of anthracnose include small brown or dead spots on the leaves, dead leaf margins and tips, large dead blotches between the leaf veins and premature defoliation may also occur. If premature defoliation occurs early in the growing season, the tree should put on new growth, so don’t be too concerned if many leaves fall off the tree this spring. This is often a problem on the lower and inner leaves and branches most heavily while the top of the tree and outside ends of branches will show little to no symptoms.

Anthracnose is a disease that thrives in cool, wet weather like what we saw this spring. The disease is less of a problem if the temperature is above 60 degrees when the buds begin to break dormancy in the spring. Anthracnose overwinters in diseased leaves and branches that are left on the ground. Be sure to always rake and destroy fallen leaves around susceptible trees. Because this disease is not very damaging to the plants, there is no need to use pesticides for control. In the summer heat the disease will fade out.

Ash rust is another disease we will be seeing soon if we haven’t already seen it in our ash trees this spring. This shows up as orange spots on the leaves. On the underside of the leaves, finger-like protrusions may develop, for the spores to spread. As with Anthracnose, this is not a harmful disease to the tree. It is best to discard all of the fallen leaves each fall and maintain mulch around trees.

We are also seeing a problem right now called Hackberry decline. Many of our hackberry trees in the area are losing most of their leaves and it looks like fall. This decline is due to many stressors to the tree such as herbicide injury, drought, poorly drained soils, and weather extremes. All of these problems have been occurring to our trees over the past few years and the combination of these problems is starting to cause problems to our trees. This is something that the tree should overcome and there is no control for it.

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