Mountain Ash Decline

For a number of years we have been getting a lot of calls concerning  mountain ash trees. People have been noticing that they seem to be struggling, the branches seem to be dying, often only at the tips. The problem that they are dealing with is a gradual decline of ash trees due to changes in environmental air quality. The symptoms of this decline include leaves that change color to pale green then yellow, or to orange and brown. These leaves will then die and dry up. The berries are also affected. They will dry up either before or after maturity. These symptoms often occur only at the tips of branches, but may also occur along entire branches. The trees abnormally retain old leaves and fruits over the winter.

To maintain your tree’s health, it is important to care for it properly. By taking the appropriate steps, you will minimize the amount of damage that occurs. The first step to take is to prune out all dead material. As with any tree, you do not want dead wood to remain on the tree. This would attract harmful insects and diseases. An important thing to remember when pruning is to sterilize your pruning tools. By dipping the pruning tools in a solution of one part bleach to nine parts water you will reduce the chance of spreading disease that you are unaware of to all your pruning points. It is also important to keep your pruning tools sharp, as uneven cuts will increase chances of diseases. To determine where the dead wood ends and live wood begins, make nicks in the branch, moving towards the trunk from the dead wood, sterilizing the knife between each cut. Once you find that there is green under the bark, you know that the wood is alive. Prune 4-6 inches into live wood, or flush with the next major branch or main trunk.

Once all of the pruning is done, spray the tree with Later’s Copper. This will protect the tree from fungal diseases. Since your tree is weakened, we suggest that you adopt a regular care routine of spraying the tree with a copper spray once every fall and once every spring. It is also a good idea to white wash the trunk of the tree on the South and West sides in order to prevent damage from the strong winter sun, which may lead to fatal fungal infections. To keep the tree strong, fertilize it once every spring with a 20-20-20 fertilizer.

Trees that are in protected locations are doing better. Our research indicates this problem is associated with a synergistic action of volatile phenoxy-acetic acid herbicides and ammonia gas. In the presence of ammonia gas the leaves take up 3 to 4 times the level of ambient acid herbicide in the air. It is unfortunate since this tree was a very attractive addition to the prairie landscape.