Many calls have come into the extension office about trees dying in home landscapes, particularly oaks. Many of the callers here lately think that wood-boring insects are the culprit for the dying trees. But more often than not the cause is related to drought stress. The damage caused by the recurring drought results in trees in yards declining and even dying throughout Clay County and the rest of the state.
Early signs of drought damage are yellowing leaves and premature leaf drop all over the crown. As the damage progresses, leaves will die from the bottom of the tree upward and from the inside of the canopy outward. Sometimes leaves simply wilt, or “burn” along their edges.
But drought is only part of the story of why trees are dying. In many cases, trees that died were already stressed from pre-existing conditions such as overcrowding, growing on the wrong site, age, soil compaction, trenching or inappropriate use of herbicides.
“If not for these factors, a large portion of the trees that died might have recovered from drought,” according to a report by Dr. Eric Taylor, a forestry specialist with the extension service.
Drought severely weakens mature trees, making them susceptible to opportunistic pathogens like hypoxylon canker and insects like the round-headed borer. We tend to simplistically blame the drought, but in actuality, it is a variety of problems that tend to combine together to kill trees.
The best defense against drought is to promote a tree’s health and vigor through proper care and management. Homeowners should pay attention to over-crowding and watering, minimizing damage to stem and roots and properly pruning.
Another problem associated with drought-stressed trees is sunscald. Sunscald injury refers to a process in which living cells just inside the outer bark are damaged by the fluctuation of day to night temperatures during the winter months. Sunscald generally affects young trees of certain species and does not affect trees with thick bark. Sunscald can result in discolored bark, bark cracking, sunken areas from lack of growth or sloughing of surface bark to reveal dead tissue within the damaged area. In the northern hemisphere, sunscald damage usually occurs on portions of the tree with south or western exposure. Sunscald injury presents an avenue for pests and diseases to enter the damaged area. Damage from sunscald may eventually heal.
This was the case in some trees I saw last week. The homeowner originally called me believing he had a borer problem. But the damage was only on the west side of the trees on the west side of the house. Upon further research and consultation with a specialist, the problem was identified as sunscald injury. The borers present were a secondary problem.
Fortunately, sunscald injury is fairly easy and inexpensive to prevent. Susceptible trees with southern and southwestern exposure can be protected by wrapping the trunk and lower limbs with white tree wrap, which keeps the bark surface temperature cooler. The wrap should only be applied in late fall before the risk of freezing temperatures and through the spring after the risk of freezing temperatures has passed.
Bottom line, determine the source of the tree problem before rushing out to purchase insecticides. Do not just assume that borers are the entire culprit because they are present. Remember that wood-boring beetles are “secondary invaders” and are attracted to already weakened, damaged or dying trees.
Unfortunately, there is little that can be done to reverse the process of a dying tree. Besides obviously watering (which is difficult under water restrictions), a good fertilization program will help preserve a tree’s vigor. In addition, drought stress also can be relieved by removing weeds and grass – which compete for water – beneath trees and replacing with a three to four-inch cover of mulch. The best defense against disease is a healthy tree.
For more information, contact the county extension office at (940) 538-5042.