A Wildfire of Insect Tree Killers
by Carol Rawle

Mountain area infested by MPB, showing three years of mortality.  Old, dead trees are gray; newly killed trees are straw yellow or orange.  Some trees may also be infested but do not turn color until nine months or so under attack.
As I look out my front windows across Gallinas Canyon, I can see many, many dead, brown ponderosa pines blemishing the otherwise vast carpet of green forest.  As I drive down any road on the ranch, the stark brown skeletons of beetle killed trees dot the roadways in alarming numbers.

During years of adequate precipitation, it will be normal to see an isolated tree here and there that might be losing the battle with Mountain Pine Beetle (Dendroctonus ponderosae), the most common and most destructive insect on the ranch.  But after last year's acute drought, the drought weakened pines are being victimized right and left.  Unless there is significant human intervention, we could easily have a beetle plague similar to what has been observed in other parts of the west in recent years where huge tracts of forest have been lost.  Forest wildfire is only one of the heartbreaking ways we can lose a forest.

Mountain Pine Beetle (MPB) attacks mainly ponderosa, lodgepole, Scotch, and limber pine.  Pinyons are susceptable to a lesser degree.  Usually, MPB singles out weakened trees, whether from construction damage, root disease, fire damage, or old age.  But the MPB populations have now increased to such an alarming degree, we can expect even healthy stands of trees to be under attack.

Symptoms of MPB Infestation

"Pitch tubes" indicating trunk attacks by MPB.  Success of the attacks is confirmed by looking under the bark with a hatchet for beetles, their tunnels and/or bluestaining.
Checking beneath the bark for MPB.  This attack was successful (note tunnels and stain).
Not all pitch tubes indicate successful attacks. Note the beetle trapped in this large pitch tube. If the majority of tubes look like this, the tree may have survived the current year's attack.
Cut tree killed by MPB, showing the characteristic bluestaining pattern.
If you find a tree with dead brown needles, it's too late to save it.  This usually occurs about ten months after a tree has been attacked.  You need to cut it down.  If the stump then shows blue-stained sap wood, you have a confirmed diagnosis.

Examine the tree trunks for "popcorn" shaped masses of resin, brown, pink, or white in color.  Sometimes, if the tree is hardy, this process of secreting resin in response to a beetle boring into the bark, will result in a beetle being trapped in a "pitch tube".  The beetle will be 1/8 to 1/3 inch long.

Look for boring dust in bark crevices or on the ground at the tree base.

If you notice a sudden flurry of woodpecker activity, you may have have beetles.  Look for missing patches of bark on the tree and bark flakes on the ground.

If you observe any of these symptoms, peal back a piece of bark with a hatchet and look for the eggs, larvae, pupae or adult beetles.

What to do About It

Larva of MPB (actual size, 1/8 to 1/4 inch).  These are found under the bark in tunnels.
At the point you discover you have an invasion of MPB, the simplest approach is to flag and remove all dead or dying trees.  You will need to chip the slash immediately.  You may want to cut up the rest of the damaged trees for firewood, but you will need to treat the logs.

The solar method is a popular one, involving no chemicals.  You can do it with or without wrapping the wood in clear plastic sheeting but you need to water the logs before wrapping.  Seal the edges with soil or duck tape.  You must place the wood, wrapped or unwrapped, in a sunny location for a minimum of two months of warm weather without stacking it.  The logs need to be rotated every three weeks.

I favor using carbaryl (SEVIN) solution, spraying the downed wood, and getting it overwith.  You can also use plain diesel oil for an impressive kill rate.  (See my previous article on Fighting the Pine Beetle.)  After exposure to the sun over the summer, the chemicals will have been neutralized so the wood will be completely safe to burn.


Large, uninfested pine being preventively sprayed.  This protects high-value trees and should be done annually between April 1 and July 1.
Removing the dead and dying trees is only half the battle.  You will need to spray the healthy trees surrounding the infested ones.  You can try to do it yourself with permethrin (Astro, Dragnet, and others) with a tree sprayer that attaches to a garden hose.  (Cheap at Walmart)

Or you can call in the pros.  It happens that C.K.  Morey will be on the ranch this coming first week of May, and he will have with him a commercial sprayer that fits in the bed of a truck.  He'll be working at Will Potter's, and the Johnsons on Owen Baldwin.  And then he will be at the Obreys up on Alpine Meadows.  For infrmation call C.K.  at work: 719-742-3588 or at home: 719-742-3492.  C.  K.  wants to help us any way he can to save our forest.

A good long range plan of prevention is to thin out the tree population, thus ensuring that the remaining trees have enough moisture and nutrients to be healthy enough to stave off future pine beetle attacks.  This also helps the forest resist the ravaging effects of wildfire.

Complacency in the presence of this potentially devasting insect is like deciding to ignore the wild fire that is roaring up the slope toward you.  The time to do something about the problem is RIGHT NOW!

For more information on the Mountain Pine Beetle, see the Colorado State University Cooperative Extension page at www.ext.colostate.edu/pubs/insect/05528.html

For more information on diseases and insects of the Pinon Pine, see the Colorado State University Cooperative Extension page at www.ext.colostate.edu/pubs/garden/02948.html