Last season bark beetles infested thousands of ponderosa and pinyon pine trees.
“This is the most we’ve seen in a long time,” said Forest Service forester, Mark Harmon, in August. “Probably forever in recorded history.”
Many trees were killed by a combination of drought conditions and beetle infestation.
“When the trees are stressed it makes them particularly susceptible to bark beetles,” Harmon said. “As a matter of fact, a stressed tree actually puts out a resin, a smell that attracts beetles.”
Much of the Southwest is now in the fifth year of what many call the worst drought to the region in 100 years.
Engraver and Western Pine beetles, both native to Arizona, attack stressed trees, laying their eggs and eating the cambium — the part between the bark and wood of the tree. The infestations commonly affected five to 10 acre clusters in the past. This year much larger areas fell victim to the bugs.
Right now, however, the beetles are in a state of dormancy and will wake again in spring. In the meantime, local foresters want to get the word out to private landowners on what they can do to protect their own trees.
“They will do their first, what we call flight, which is when they leave the tree they’re currently in and go to a new tree, sometime in the spring,” Denk said.
When that flight takes place varies depending on weather conditions, she said.
For now, Denk says there’s plenty landowners can do to protect their most valued trees.
“This would include removing trees that are obviously infested and getting that wood off the property,” she said. “Also doing some of the preventative spraying that can be done.”
One expensive option is to spray individual trees with insecticide that will guard against beetle attacks. The problem is that trees must be sprayed top to bottom, which many people won’t be able to do on their own. Hiring a professional to spray can cost $80 or more per tree, Denk said.
The high cost of spraying eliminates it as an option on a forest-wide level, Denk said. Instead, the Forest Service is focusing on thinning the over populated forests as a long-term solution.
“Our major objective remains thinning,” Denk said. “What we need to do on a forest-wide level is to continue thinning projects we already have in place and also to look at thinning projects in really high-value areas.”
Less costly measures revolve around helping trees build up their natural defense mechanisms. Watering individual trees will make them stronger and better able to produce pitch, a sticky, sap-like substance produced by the tree to expel attacking beetles.
“It should be a slow, deep soaking,” said Joel McMillan, a Forest Service entomologist “It can’t just be a quick sprinkle with a law sprinkler.”
“The trees’ natural defense mechanism against the beetles is to pitch them out when (the beetles) are attacking,” said Denk. “But without any moisture in the tree, the tree has lost that defense mechanism.”
Foresters have seen holes in trees where beetles bored into the trunk where no pitch was produced at all.
“The tree actually made no attempts to get rid of the beetles because it had no moisture,” she said.
The problem facing foresters now is, according to Denk, that even a much healthier forest would have a tough time combating the numbers of beetles expecting to wake this spring.
“The beetles are always there,” Denk said. “Say in a normal year, a tree has 50 beetles attack it and it’s able to pitch those beetles out. Well, this year, even if trees have more moisture because of thinning projects in the area or because of moisture received, there’s still going to be 10 times that number of beetles attacking.”
The Forest Service currently has thinning projects going, and is planning six more projects in the next few years. Those plans will cover more than 30,000 acres of forest land. In the meantime, the bulk of the solution lies in Mother Nature’s hands, Denk said.
“We’re going to have to see several wet years and we’re going to have to really push up these thinning projects,” she said. “This is not a short-term solution on a forest-wide scale. It’s going to be a long-term process.”