Q: I think some of the trees and shrubs in my landscape are dying. I've noticed browning leaves and a thinning canopy on one of my maple trees and some of my yews starting to turn brown and the foliage is thinning. Is there some disease that is killing trees and shrubs?
A: Although I can't be absolutely certain, I suspect that what is happening is very much related to the environmental conditions we have experienced the past couple of years. Specifically it is the combination of a very wet year last year followed by this year with very hot and dry (drought) conditions.
We often say that certain plants don't like "wet feet" and that they need to be put into well-drained soil. This holds true for certain species of trees and shrubs as well. Some of our hardwood maples might fit into this category and yews certainly do. If environmental conditions are not extreme, the homeowner can sometimes get away with putting these trees and shrubs in less than ideal locations and they do OK. When we get some above average wet years, these plants are likely to lose some roots due to some root rot disease organisms such as phytophthora. These organisms thrive in wet and poorly drained soil and attack roots, causing root dieback. If the next year is closer to average in terms of moisture and without a lot of heat stress, then the plant may recover somewhat and even produce some new roots. However, if the succeeding year happens to be very hot and dry, the plant is not able to recover and add new root growth. As a result, the plant does not have an adequate root volume to enable it to survive a drought.
Rory Lewandowski is an OSU Extension Agriculture & Natural Resources educator and may be reached at 330-264-8722.