If you have had ash trees dropping their leaves like rain drops in your yard, do not panic. It is more than likely caused by anthracnose. Anthracnose is a fungus that causes some problems in all sorts of trees. In our area, it seems to bother ash trees the most. It can cause some of the same symptoms in other types of trees too which are: maples, ash, birch, black walnut, butternut, buckeye, elm, hornbeam, and oak. If you pick up the fallen leaves you will see brown, sunken edges of the leaves. You will also see leaf drop where the leaves fall from the trees (don’t worry! Most trees will replace some of the leaves later this summer) with the largest areas in a canopy of a tree affected are the lower and inner branches.
If your trees are healthy, this will not affect them. It will just make a mess out of your lawn. You will not need to treat unless you have a sick tree or if you have a small tree. The only other time you would need to treat with a fungicide is if the tree has been affected by anthracnose for more than 3-4 years in a row.
Generally speaking, anthracnose occurs in years when the weather is cool and wet in the springtime. In the fall, it is a good idea to make sure to rake up leaves that may have fallen from any trees affected earlier in the spring and compost them. Leaving them on the lawn may keep the lifecycle going for the fungus. Anthracnose is known to keep progressing in walnut and hornbeam though the growing season. A tree may end up looking pretty tough come fall but with some good leaf raking, the next year will turn out just fine.
This is a good time to remember that when something happens in our gardens that knowledge is power. We have to remember to start asking questions, not only of your local Master Gardeners, but also your local extension personnel or your local greenhouse managers. We need to make sure that we are choosing the right treatment for the right disease or insect.
I have had many questions about ash anthracnose because we think it is Emerald Ash borer (EAB). This is a good time to review how to identify Emerald Ash Borer (EAB). The first step is to make sure that the tree you are looking at is, indeed, an ash tree. The second step is to make sure that you do not confuse Emerald Ash Borer with other Borer insects. According to the U of M website, “EAB larvae create winding, S-shaped galleries in the outer sapwood and in the tissue (phloem) that carries food from the leaves to the rest of the tree. Not all galleries in ash are caused by EAB. These tunnels girdle the trunk and branches, interrupting the flow of water and nutrients. The S-shaped galleries become visible if you remove the bark on the trunk. Adults emerge in spring creating small, one eighth-inch D-shaped exit holes. These holes might not be visible right away.” This is just the first year. They can be hard to find!
The second year is when a gardener can start to see the larger picture. The thinning canopy of a tree will start to give it away. You may even see our woodpecker bird friends trying to feast on the larvae of the EAB, which is also another give away that it is time to do something. If left untouched, EAB can possibly kill a tree within four years of initial infestation.
The hard part about EAB is that it often looks like so many other things. Ash trees, in particular, seem to suffer from all sorts of problems including branch die off and dead branches in the canopy. This happens when the tree is under some sort of weather stress such as drought or flooding. For more information on anthracnose go to: https://extension.umn.edu/plant-diseases/anthracnose-trees-and-shrubs. For more information on where EAB is within the US, go to https://www.aphis.usda.gov/plant_health/plant_pest_info/emerald_ash_b/downloads/eab_quarantine_map.pdf
Again, it never hurts to ask to make sure that if you have problems in your yard and garden, there are many people in our community who can help you figure things out. For more information on gardening or becoming a Master Gardener, please email me at firstname.lastname@example.org
Ash leaves on the ground,
Photo Stephanie DeJaeghere