Drought stresses trees in our landscapes and on the hillsides. Stressed trees attract bark beetles, which can kill trees. Bark beetles also survive on newly dead or dying trees. Sometimes they will attack living trees.
When few beetles are present and trees are healthy, trees push the beetles out with their pitch. However, when trees are stressed, they cannot produce enough pitch to force out the beetles. Beetles also carry fungal diseases that they pass on to trees they attack.
Damage, whether caused by wind, lightning, drought, ice, snow, insects, construction, or equipment such as weedeaters, weakens a tree. The tree then sends out a chemical "S.O.S." Beetles pick up on these signals and fly in for supper.
There are many species of beetles, and generally, specific beetles seek specific kinds of trees. Jeffrey pine is susceptible to the Jeffrey pine beetle. Pinyon trees are particularly susceptible to the pinyon ips, though several other beetles also attack pinyon.
Infested pine trees become next year's source of infestation. Identify freshly attacked trees from pitch globs, small holes, and boring dust. In addition, the tree color may fade.
If more than half of a tree's circumference has been infested, it can't be saved. No chemicals are registered to kill beetles under the bark. The tree should be cut down, debarked, burned, hauled away, or buried. Note that beetles can often survive in firewood.
To protect trees, avoid damaging them. Keep them irrigated all year, including during the winter, if there is no snow or rain.
Carbaryl insecticide can be used as a preventative spray for high-value trees, but usually a certified pesticide applicator with boom equipment is required to reach the upper portions of the tree. Carbaryl is highly toxic to bees. Treatments applied to the ground have not been shown to be effective. (This information taken from "Bark Beetles - Are Your Trees At Risk?, " U.S. Forest Service Forest Health Protection - Intermountain West, 34.08.400.09/06.)
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• Join me for a guided tour to find out how to landscape for wildfire defense 10-11:30 a.m. today, at 4001 County Line Road in Carson City. This is our Defensible Space Demonstration House.
• From 5:30-7 p.m. June 12, meet me at the Carson City Community Garden, 1044 Beverly (east of the cemetery) for a tour and talk about growing vegetables. There are a few garden plots remaining at the community garden. The fee is $10, and you must be a Carson City resident.
For information on the community garden or gardening, contact me, 887-2252 or skellyj@unce.unr.edu, or your local University of Nevada Cooperative Extension office.
• JoAnne Skelly is the Carson City/Storey County Extension educator for University of Nevada Cooperative Extension.