Forest Health - Bark Beetle

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Background Information

How serious is the problem?

The level of Ips beetle infestation in the Ponderosa Pine vegetation type has reached epidemic levels on the Prescott National Forest. Preliminary estimates released on October 27, 2003 indicate that Ips-caused mortality of ponderosa pine has increased to nearly 93,000 acres. An increase of 18,000 acres from 2002. In the Crown King/Horsethief Basin area, approximately 60 to 70% of the Ponderosa and Pinyon pine have been killed.

[Photograph]: Enlarged image of an Ips beetle.  Actual length is 5mm.

Where do these beetles come from?

Under normal conditions, there are usually endemic populations of Ips beetles present in the forest. Healthy trees are often able to withstand attack from these beetles by expelling the insects in the sap as they bore into the bark of the tree. Trees weakened by drought, over crowding, disease or fire are more susceptible to beetle attack. The beetles girdle the tree by boring galleries in the cambium layer where they lay their eggs. The eggs are laid from April through September. The larvae hatch, mature, and fly to adjacent green trees where the cycle repeats itself.

Where are the infestations?

The areas hardest hit are Crown King, Prescott Basin and Mingus Mountain. The current aerial flight shows a significant increase in Ips mortality within the city of Prescott. The Coconino, Kaibab, Tonto, and Apache-Sitgreaves National Forests are also experiencing serious beetle infestations.

How does the mortality from Ips beetles increase the fire hazard in the wildland urban interface?

Future impacts from heavy accumulations of dead and down material have been described well by research. These impacts contribute to very high and extreme fire intensity, extreme fire behavior, fire persistence, resistance-to-control and burnout time. High intensity fires may cause major detrimental impacts to wildlife habitat, watersheds, the soils and associated microorganisms. There is potential for high fuel loading to occur within the next 5 years in the project areas from dead and dying trees due to drought stress and bark beetle infestations. In addition when the trees fall, they would become “jack-strawed”, making fire suppression difficult. Removing dead and dying trees from the project areas would reduce the potential for heavy accumulation of fuels and decrease fire risk.

Why can't the Forest Service stop this infestation?

Stopping a landscape level bark beetle infestation is, for all practical purposes, impossible. While chemical treatment (spraying) can work on individual trees that are not yet infested, it is very expensive and not practical on large pieces of land. The entire tree must be saturated with the spray in order for it to be effective. The cost can run from $25 to $80 per tree depending on the size of the tree and the location. Spraying must be repeated annually prior to the beetles flying in April. Epidemics normally last several years and are stopped only when the cycle is broken. Until we receive sufficient moisture to return the trees to a healthy state, thinning and prescribed burning can potentially stress the trees.

What should be done with the trees on my private land that have already been killed by the beetles?

Because the beetles “winter” in the trees they have killed, cutting the infested trees before the new crop of beetles flies in April is essential. All wood over 3” diameter must be removed from the area (to a location without coniferous trees) or the bark stripped from the wood to kill the brood. Smaller trees may be chipped. The chipped material should be removed from the area, because the scent from the chips may attract the beetles. If they are not cut and removed or treated, the brood will hatch and fly to adjacent green trees.

What can I do to protect the trees on my private land?

While there is no guarantee that any treatment will prevent your trees from being infested, there are actions you can take to minimize the possibility. Proper deep watering of the trees can help to keep the trees in a healthy condition; however, there are economic and environmental costs to be considered with this use of water. The City of Prescott Arborist may be able to provide advice on deep watering. Annual spraying while expensive can be effective, but must be done by a licensed professional. The County Extension Agent and the University of Arizona have information available to private land owners to assist them in dealing with the IPS beetle on their private lands. Contact the County Extension agent, Jeff Schalau at (928) 445-6590.





https://www.fs.usda.gov/detail/prescott/landmanagement/?cid=fswdev3_009832