Mountain Pine Beetle Different in Urban Areas by Mary Small

For about three years, mountain pine beetle has been found in the urban corridor.  Arborists and city foresters have been watching the hit trees carefully and are taking steps to keep the pest contained. What they’ve learned is that MPB behaves differently in the city than in the forest. In the urban setting, most of the trees with beetle hits are Scotch pine. A much smaller percentage include ponderosa pine and other pine species. Even with lodgepole or ponderosa pine nearby, the insects heard for Scotch pine!

Ralph Zentz, city forester in Fort Collins, calls this distinct attraction to Scotch pine a fatal one for the beetles. These pines produce copious amounts of resin and are usually successful in “pitching out” (and drowning) the beetles. In most cases (in Fort Collins, about 90%), pines that have been hit by beetles actually survive the attack. In the forest, these pines would be considered “goners”.

Trees in urban settings are usually watered more thoroughly or more often than their counterparts in nature. Trees use the water as a component of the resin, so more water equals more resin and more resin equals more successful pitch-outs. There is less competition for resources in the urban setting than in the forest, producing a healthier tree (they aren’t spaced so closely). Many pines are also treated for a variety of pests.  Some of these applied chemicals may help protect them from MPB.
At this time, there is a low-level epidemic in ponderosas along the Front Range. They are found most-
ly in lower elevations, but closer to town than the lodgepole pines of higher elevations. More com-
munities are reporting MPB presence than in past years. Foresters believe that the newer infestations
are coming from the infested native stands, wood stockpiles or other, unidentified infested trees in our
communities. It’s a good bet that a lot of beetles are inadvertently brought in on firewood.

As Master Gardeners, here are the messages we need to communicate to our urban citizens:

Don’t transport infested firewood.  Non-infested trees are “red (needles) and dead”.  Green and fading trees are not okay!

Remove only trees that have been successfully attacked.  It may not be possible to tell that until February or March. Successfully attacked trees will generally have air holes above the pitch tube sites about every 6 inches; woodpecker activity; loose bark; long vertical galleries packed with frass under the bark; blue stain; and horizontal larval galleries under the bark. 

There are no curative treatments, but preventive sprays may be applied in May or June. They include carbaryl, permethrin (Astro) or bifenthrin (Onyx).  It’s best to have an arborist make the pesticide applications.