Magnolia virginiana disease

Asked April 1, 2020, 10:42 AM EDT

M. virginiana with failure to leaf out across entire shrub with blackened spotted stems. Leaf drop mostly complete although buds are forming. THis was a shrub acquired with a U&CF grant for our municipality and we are hoping for a diagnosis to facilitate replacement.

New Castle County Delaware

1 Response

There are several fungi and bacteria that can cause leaf spot in sweet bay magnolias. To find out what exactly is infecting yours, you will need to take a sample into the plant diagnosis clinic, which is currently closed because of covid19. So, if possible, the next best option is to prune and clean up fallen leaves. First prune out the diseased parts of the tree, cutting where the tissue is healthy beyond the disease and cleaning the pruning shears after each cut with alcohol. Then, rake up all the fallen leaves and dispose the pruned branches and leaves. If new leaves open and show leaf spots, it would be prudent to spray with a copper based fungicide, following label instructions. This will not cure spots but will prevent more from forming.

Newly transplanted trees are stressed trees and these are more likely to get a disease. If the whole tree is not infected, chances are good that it will recover but it will take time. Magnolias may also be stressed by finding themselves in soil that is too damp or by being crowded so that there is not enough air circulation. If you believe the site is the problem and must replace the tree, it would be best to plant something different.