Bare limbs at the top of a tree can indicate tree decline, a downward spiral in health that usually leads to the tree's death. BILL SEVIER/Courtesy
Q: I have a large shade tree, and last year a few limbs in the top did not leaf out. This year there are more bare limbs. What could cause this? Louise, TulsaA:
Your tree is likely developing a condition called "tree decline." Like the name suggests, this is the beginning of a downward spiral in the tree's health usually leading to tree death.
Tree decline does not have a single cause. It often is the result of some primary stress followed by pests that may take advantage of the tree's lowered resistance.
Primary stress factors that may start the decline include weather extremes, building construction activities, insects, diseases and herbicides.
Activities associated with building construction often cause soil compaction related to heavy equipment and damage to roots due to trenching. Frequently, tree roots are smothered when fill dirt is spread over their root zones. It may take five years or more before trees begin to decline due to these activities.
In our area, a large number of mature trees are in decline related to the terrible heat and drought we have had the past two summers. The effects of this drought stress will continue to be seen for years to come, even with "normal" summers.
Trees in early decline produce less energy and rely on energy reserves to survive; after those reserves are depleted, trees are susceptible to other secondary problems such as disease and insects.
Early in the decline process, all that may be evident are smaller than expected leaves with premature fall coloring and leaf-fall. Often leaf scorch (brown leaf edges) is noted in summer along with noticeable twig and stem dieback. Later, larger limbs fail to leaf out and sucker growth (small sprouts) develops on limbs and tree trunks. These are all signs of the tree's stress, and at this stage it is obviously in trouble.
The next phase in the progression of events is usually the development of a fungus or infestation with insects such as borers. For oak trees, hypoxylon canker is a common killer in this spiral of events. This disease primarily affects oaks but can infect other trees, as well. It is always fatal.
Once the decline is in progress, there is little one can do other than to make sure the tree has periodic deep soaking watering. No treatment is usually available or indicated for fungal infections.
For a valuable tree in decline, an ISA-certified arborist should be asked to consult and give recommendations about either restorative care or removal.
If you have a garden-related question you would like the Master Gardeners to answer in a column, call 918-746-3701.
Garden tips
When irrigation water is limited, set priorities. Trees and shrubs are more valuable than ornamentals and lawns and should get preference. Long and slow watering in the drip line of trees is best. Try to moisten the soil down to 12 inches.
When watering by hand, try to water the root area of plants, not the leaves. Water on leaves promotes diseases. Also, if you water in the early morning, there will be much less water loss from evaporation.
Cucumbers are often bitter this time of year, and vines quit producing. This is due to the heat. If you are able to get the vines through the summer, after it cools, they will be fertile again and the taste of the cucumbers will improve.
Some trees such as sycamores and river birches lose large numbers of leaves in the heat of summer. Trees do this to reduce water loss from their leaves. The tree is not dying.
Original Print Headline: Bare limbs a sign of decline
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