Effects of bark beetle invasion still strong throughout northern Arizona<br>
Five percent of the ponderosa pine and seven to eight percent of the pinon pine have been killed by bark beetles on the Kaibab National Forest, Mark Herron told the Rotarians during their Dec. 5 meeting.
Herron, a forester for the U.S. Forest Service, said the bark beetle infestation of the forest has been aided by five years of drought. According to tree ring studies, the forest is suffering through the driest period in 500 years.
Half of Williams’ annual precipitation normally comes in the form of winter snow pack. Thawing snow soaks deep into the ground where tree roots can reach it. The winter of 1995-96 was the first year of the current drought in which Williams failed to receive adequate snow. The drought of 2002 is the worst on record.
When trees are weakened by drought, they become susceptible to the pine engraver beetle. The pine engraver begins its infestation at the top of the tree. The beetles bore under the bark and lay large numbers of eggs, which hatch into very small larvae that chew through the tree’s inner bard and food-conducting tissues thereby girdling the tree.
After the tree has been further weakened by the beetle infestation, the tree becomes a prime target for the western pine beetle. Eventually, after the two infestations, the tree dies, said Herron. Within two to five months after being attacked, most pine needles turn from a pale green color, to straw tan, to reddish brown. The tree is essentially dead after the first signs of fading to a very pale green.
Trees that grow on rocky sites and volcanic cinder cones suffer the most. Because of their location, these trees receive less water than trees growing in areas such as meadows. Thus, these trees weaken quicker even under the best circumstances, Herron said.
Another factor promoting beetle infestation is the high density of the forest. The Kaibab National Forest is 10 times denser now than it was at the turn of the century. Trees that grow closer together are more likely to be attacked by beetles, said Herron.
Once dead, the trees become a fire hazard. Forest officials are concerned about the potential fire hazard coupled with the density of the forest, Herron said.
The most effective way to stop the beetle infestations is a hard winter and plenty of moisture. Returning the forest to its natural state — less density by thinning the trees — is another solution the forest service is pursuing, Herron said.
The forest service offers several tips for property owners who are attempting to avoid or manage a bark beetle infestation. If you already have a beetle infestation, the most direct means of controlling this pest is to cut down obviously sick and infested trees, removing them as soon as possible. Once a tree is infested, nothing can save it — not even extra water.
If left standing, new generations of bark beetles can breed and spread to more trees within one to three months from the time of the initial attack. Quickly destroying beetle brood trees can help save the other trees on your property and those of your neighbors. Don’t be fooled by tree service companies that claim they can save your infested trees with chemicals, or by cutting off a dead treetop.
If you hire someone to cut your trees, or if you cut down your own trees yourself, be sure to immediately either peel all the bark off or “buck” it (cut into 14 inches or shorter lengths) and split the wood and spread it out in full, direct sunlight for at least six months before stacking. You can also contact a sawmill that will debark and use the logs soon after they have been cut. Stacking logs against other live trees almost guarantees that beetles will infest those trees also.
One species of the bark beetle prefers to breed in freshly cut small trees, branches and top trimmings that are left after land clearing and tree thinning operations. The pine engraver beetle will use this fresh material when it is created from January through July.
Therefore, it is best to do your thinning jobs only from August through December each year.
Mulching it in a chipper should clean up fresh slash debris. Fresh chips should not be left piled next to other live trees because they release odors that attract beetles to live standing trees nearby. Spread chips in a thin layer in full sunlight.
The best control is prevention. Keep your trees healthy by thinning them out properly. While trimming your trees is an excellent long-term preventative measure, just thinning alone may not be enough to protect trees from bark beetles. In order for the leave trees to benefit from thinning, they need water before beetles start an attack.
Slow, deep-soak watering of yard trees from March through late June can help them survive in drought years. Fertilizing trees when they are too dry does more damage than good.
If preventative bark surface sprays are used, they need to be applied before early April, when beetles begin flying in the spring. Use of insecticides to prevent these pests can be very tricky, and needs to be done only by a certified pesticide applicator that is training in bark beetle life cycles, behavior patterns and the correct mix of chemicals. Such sprays will not kill beetles once the bugs have already entered the tree. Systemic insecticides injected inside the tree also do not work.
For more information concerning prevention measures or identifying infested trees, contact Coconino County Extension Agent Tom DeGomez at 774-1868.
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