Treat at risk trees for mountain pine beetle soon

Farm Forum

BROOKINGS – When it comes to trees, we do not have many pest treatments to begin at this time of year. Most diseases have already infected the foliage and foliar-feeding insects and borers have already come and gone or have burrowed into the protective inner bark or wood. However, in the case of treating trees infested with Mountain Pine Beetles or Dendroctonus ponderosae, we have a treatment which can still be initiated, says John Ball, SDSU Extension Forestry Specialist.

Mountain Pine Beetles attack trees in mid-summer, the flight often peaking just before Rally week, and the eggs are laid in the inner bark. The small, white, grub-like larvae soon hatch and begin to feed, which continues until late spring of the following year before they become pupae and then adults.

Ponderosa pine trees attempt to defend themselves by producing resin to “pitch” the adult beetles out as they burrow in.

“Sometimes you can find a successful pitch out with the beetle still stuck in the whitish brown glob of resin,” Ball said. “However, far more often the lower 15 or 20 feet of the tree is covered with dozens of pitch masses aligning the trunk, evidence of a successful attack.”

Ball says attacked trees die by the spring following a successful mass attack by the beetles. These trees can not only be identified by the numerous pitch masses formed last August as the beetles burrowed in but by the foliage which is now becoming discolored. Later this summer as the adult beetles fly from their now-dead hosts, the tree will have red needles that turn ashen-gray and drop by the second year.

Spray before attack

High-value trees, those surrounding a home nestled in the Black Hills forest, can be protected by pesticide applications only if the spray is applied before the beetles attack.

“The window for spraying a pine to protect it from attack is rapidly coming to a close,” Ball said. “A check of insect development last week found that most of the mountain pine beetles were still larvae but a few pupa had already formed. Based upon this development, the first adults will probably be flying sometime in mid-July. This means the spray should be done within the next week or two.”

Application tips

The trunks of the trees to be protected must be sprayed to from the ground to a point on the trunk where the diameter narrows to 5 inches or less. This means the sprayer must reach at least 30 feet or more on mature trees, a distance that requires a high-pressure sprayer, at least several hundred pounds per square inch (psi).

“Most small sprayers either cannot reach that high or at that distance will some mist the bark rather than have the pressure necessary to soak the bark to runoff. The pesticides to use for treating the trunks are those containing either bifenthrin, carbaryl or permethrin as the active ingredient and use only formulations specifically for listed for controlling bark beetles,” he said.

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