Hopefully you were able to take a look at last week’s article discussing what to do if you are seeing plant dieback in your trees and shrubs. If not, the short version is: we have to identify what the cause of the trouble is before we can find a solution, so call (706-359-3233) my office to schedule a farm call OR email (rlstew2@uga.edu) me as many details as you can come up with to get the process started. This week, I’d like to discuss some of the most common causes of tree and shrub decline that I see.
Some causes of dieback primarily affect new plantings. Improper soil pH and fertility, which can easily be correct with a soil test, lime, and fertilizer, can cause yellowing (chlorosis) and limb dieback on new plantings. Some trees and shrubs are more tolerant of pH extremes than others, but most prefer a pH between 6-7. A second problem is improper planting depth – most often, planting too deep. The base of trees and shrubs have an area where they flare and roots begin growing. When planting, place that tree flare right at the soil line – be mindful that the tree may settle a few inches as the soil compacts back down. Planting too deeply will cause branch dieback in a few years, and it cannot be corrected other than digging them up and replanting them. A third issue is girdling roots. When a plant is grown in a plastic container, it develops a root system that circles the inner wall of the pot. You need to trim, remove, or redirect these roots at planting or else they can encircle the trunk of the plant, cutting off water and nutrient transportation.
Other causes of dieback can affect plantings of all ages, but occur due to human activity. The root zone of trees and shrubs is roughly as wide as the plant is tall, and is easily damaged. Most commonly, the root zone is damaged from digging or trenching when building or compaction from construction or vehicle travel over the area. The damage from these activities is slow to appear. If you are doing construction or building near a shrub or tree, keep machinery out of the root zone as much as possible. Similar to root damage, trunk damage can occur from string trimmers, mowing or animal feeding activity. When the trunk of a tree is damaged, the flow of water and nutrients stops, causing parts of plant to die. Nothing can be done to fix this damage once it occurs, so using a physical barrier to help prevent damage is key. A final human-caused issue is herbicide damage. While rare, herbicide overspray can injure non-target plants. Depending on the severity of the damage, the tree may or may not survive. Be sure to follow good pesticide application practices if you need to use herbicides near your trees.
The last few stressors are water, disease, and pests. Water can be a cause of decline for trees and shrubs – both not enough, and too much of it. Dry soil conditions can be caused by drought or lack of supplemental irrigation, which is particularly important for young trees (less than 5 years old). Too much water can also cause problems for trees planted in compacted or poorly drained, low-lying areas. Prolonged moisture causes root diseases and damage, which ultimately shows up with dieback in the canopy of the plant. Be sure to consider the species of plant you install if you know you have wet conditions, as some are more tolerant of “wet feet” than others. While many people expect disease and insect damage to be the cause of an unhealthy plant, they’re often not the biggest culprit. Most plants are not going to be targets for disease and pests until they’re already in decline. Diseases can be vascular (affecting the whole plant), root rot, foliar (leaf related), and caused by bacteria, viruses, and fungi. Insect pests such as borers, scale, and aphids can also cause plant damage and dieback. Both disease and insect issues need to be properly identified before an appropriate treatment can be recommended.
If you have a plant in decline, these are some of the potential factors contributing to that. In my experience, it is rarely a single thing causing a problem, but typically a combination of problems that results in an unhealthy plant. If you need assistance with your landscape, please let us know at uge3181@uga.edu or 706-359-3233.
