Q: My old maple tree has a few dead, bare branches at the top, and next to them, there are a couple of branches with leaves that started turning brown and getting their fall color in the middle of the summer. What can I do to save the rest of the tree? This summer was dry, but we did try to water the tree a couple of times.
A: When any tree has a discolored branch, it is waving a flag that says "help me." In fact, arborists call the condition where a branch or two displays fall colors any time it is not fall "flagging." The flagging branches are letting you know that the whole tree is in danger. Now you have to be a detective and determine what the danger is.
The bare branches on your tree this year mean that it was waving a flag last year, if not the year before. Droughts and other physical damage don't often kill mature trees by themselves. But they do let in numerous insect and disease organisms that do eventually kill trees.
Trees with less water than they need from their roots will conserve water by closing the pores on their leaves. They will then drop leaves to conserve more water. Eventually, they will drop whole branches. Large mature trees can have a couple of months' worth of water stored in the trunk, but that doesn't mean they can go for months without water; it just means they will do what they can to survive. Usually drought damage appears throughout the tree, not just on a flagging branch.
When a tree that is not full of water bends in the wind, it creaks and moans, because the normally wet and elastic tissues supporting the trunk are not lubricated with water. Try breaking a green stick and it just bends, but try breaking a dead stick and it makes all kinds of noise as it bends and breaks. A tree that is not full of water will also release a fragrance as it bends, because those formally wet cells are now breaking apart.
These sounds and smells attract insects, especially insects that bore into tree trunks. A wet trunk could release enough sap to drown the insect, but a trunk in need of water can make a good home to a borer. Boring insects are borers during the larval stage. The adult female flies from tree to tree to insert her eggs into them. If she picks up a fungal-disease spore from one tree, she can transfer it to another tree.
The larvae of borers eat the tissues that transfer water in the tree. The branch does not get water out to the ends from the point of attack, where the female laid her eggs. The leaves wilt, maybe turn colors and die.
If a fungal disease is present, it plugs up the tissue that transfers the water within the tree. Some diseases move slowly and kill one branch at a time; others move rapidly throughout the tree, killing it within in a year or two. In either case, the leaves on the branch wilt, maybe turn colors and die. As the fungus spreads, the branches next to the original one follow the same pattern.
In general, the boring insects and fungal diseases are best treated with chemicals that soak into the tree and move within it to kill the organisms in the visibly affected branches and the invisibly affected branches. Unfortunately, many of the insects and especially some of the diseases are very difficult to treat and completely remove.
Scale insects can grow to huge populations that can also cause flagging. Any tree that adds some value to the landscape should be looked at by a licensed arborist to get a proper diagnosis on what is causing the flagging branches and what the best method of treatment will be. Trees out in the back 40 may be better off left to fend for themselves, maybe with a little extra fertilizer and water, because it can be expensive to treat trees for several years.
Email questions to Jeff Rugg at [email protected] To find out more about Jeff Rugg and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.