There have been several samples of arborvitae brought in over the past few weeks. In each case, there were brown spots showing up on the shrub. I inspected the samples but could not find any evidence of disease or insect problems. This led me to think it must be something in the environment. What could have happened in the environment to cause brown spots to show up on evergreens? If you think back over the last year or two, a lot of stress has occurred in our landscapes.
Discolored needles or loss of foliage in stressed evergreens is often not immediately apparent. In fact, it sometimes shows up a year or two after the stress has occurred. Typically, foliar discoloration and branch dieback can be attributed to one or more factors related to where the tree or shrub is planted.
- There is excessive moisture in the root zone. With the amount of rain we had last spring, this may be causing the current damage.
- There are compacted soils around the tree roots. The soils in our area have a heavy clay content and could easily be compacted.
- Excessive dryness in the root zone. Remember last summer? It didn’t rain for several weeks.
- The soil pH is either too high or too low. In our landscapes here in Madison County, the soil pH tends to be over 7 (alkaline), which is not the best type of soil for some trees and shrubs.
Other factors can contribute to stress as well, such as improper planting, damage from de-icing salts, or trunks being injured from mowers or string trimmers.
What can be done if your evergreens have brown spots? Unfortunately, there are not a lot of options. New needles will not grow back to replace those that have fallen off. To determine if a browning evergreen will produce new growth, check the buds at the tips of the branches. If they are still green inside, growth will likely occur in the spring.
In the future, be sure to choose the right tree or shrub for your location. Different species of plants require different things to thrive. For instance, some can tolerate growing in wet areas while some cannot. So before choosing what to plant, do your research as to what works best for your property.
Submitted by Amanda Sears, Agent for Horticulture, Madison Co. Cooperative Extension Service