It has been a long, hot and humid summer, and fall is coming soon. Between storms, waterlogged soils and heat, this summer has been particularly stressful for our trees. Lately, there have been several calls to the Duval County Extension Office regarding dead branches in trees in the landscape. There are many reasons why branches can die, and it’s important to understand why in order to understand the next steps.
If you notice areas of recently killed branches with brown leaves in your tree, the first thing to do is to observe if the damage is on a large part of the tree, a small branch, or a twig. If a large section or branch of the tree has turned brown, the branch may have been recently struck by lightning.
Lightning can injure a tree in several ways. Most of the time, the damage is obvious.
The heat of lightning vaporizes the water from the tree, instantly transforming it into vapor. The resulting pressure of the rapidly expanding hot steam blows the wood from the tree to pieces. Most of the time this happens towards the outside of the tree, and we see it as a trail along the bark.
Sometimes the damage is not so obvious. We cannot see the damage because it affected the root system or the interior of the tree. The other thing to think about is that lightning is never the same. A tree can be given a minor strike, a major strike, or hundreds of variations in between.
The true extent of the damage to the tree is not immediately evident immediately after impact, as lightning occurs in an endless range of voltages and temperatures. However, once the extent of the damage becomes apparent, a decision must be made as to whether the tree can / should be salvaged. An ISA certified arborist should be consulted to determine if the tree can be pruned or should be removed. You can find an ISA certified arborist at www.treesaregood.org. In the meantime, timely irrigation and light fertilization are helpful in helping the tree compartmentalize the damage.
If you notice that a smaller branch is dying, look inside the tree and observe the branch very closely. If you see a spot on the branch where the bark has been torn from the branch, the damage is likely caused by the squirrels. If you prune the branch and watch it closely, you might even be able to see the tooth marks the squirrel made. Damage usually occurs in the spring, but is not noticeable until summer when the branch turns brown.
It seems that once a squirrel finds a tree they love, they come back to it over and over again. Injuries from bark pulling and branch ringing inhibit the branch’s ability to transport water and nutrients from the roots to the leaves. This results in the death of the branch.
There are several ideas as to why the squirrel would do this to the tree. Ideas include everything from using tissue with sugar-rich sap to get the much-needed nutrients, to gravid squirrels chewing on the branches for pain relief. Recently, a research article in the Journal of Forest Ecology and Management stated that squirrels use the calcium in the sap to compensate for a calcium deficiency in their diet.
More research will be needed to see if and how we can add calcium to their diet so that they stop damaging trees. If you have squirrel damage, simply prune the dead branch where it attaches to a larger branch. The pruning cut should be made just outside the branch collar.
If the damage you notice consists of several leaves on a small, pencil-sized twig dying (also known as an alert), then the culprit is more than likely the black twig borer. The female black twig borer pierces the small twig to create a gallery where her eggs are deposited. She also cultivates a mushroom in the gallery that the young larvae will use as food.
If you carefully inspect a bending branch, you can usually find the hole the black twig borer made in the twig. It is very small (less than a millimeter). If you break the twig at the hole, you will see the gallery in the center of the twig. Sometimes you even see a beetle in the gallery. There is no treatment for this insect other than pruning and destroying infected twigs. The good news is that this pest is not going to kill your tree. Trees can easily recover from minor damage caused by this insect.
For more information on this or any other landscape, lawn or tree issue, go to âAsk IFASâ at https://edis.ifas.ufl.edu/ .
Larry Figart is an Urban Forestry Extension Officer at the University of Florida / IFAS.