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Colorado State Forest Service News

March Is Good Time to Check for Mountain Pine Beetle

side by side images of a ponderosa pine trunk and a close up of pitch tubes in the trunk that indicate infestation by mountain pine beetle
This ponderosa pine tree’s trunk has the popcorn-shaped pitch tubes that indicate an MPB infestation. On the right you can see the pink/red color of pitch tubes. CSFS photo/Randolph

FRANKTOWN, Colo. – March is an ideal time for landowners to check pine trees, specifically ponderosa, on their property for the presence of mountain pine beetle (MPB). Each year, MPB take flight in late summer to look for new host trees. After this peak flight period, by October enough time has passed to see signs of infestation, and the following March is then a good time to check trees and remove them if necessary. 

What to Look For

MPB  leave some easy-to-identify signs that they’ve infested a tree. If you see these two diagnostic signs on your trees, you’ll know that MPB have bored into the trees.

  • Pitch tubes: These look like popcorn, but they’re actually globs of sap. Sometimes healthy trees can flush beetles out with their sap, but if you see multiple pitch tubes or tubes that are red or pink, there’s a good chance that the beetles have successfully infested the tree.
  • Frass: Look around the base of the tree and in crevices in the bark. If you see sawdust, it means that the beetles have been boring into the tree’s bark. 

Pro Tip: Start your inspection near previously attacked trees. You can recognize them from their dead, orange crowns. MPB are more likely to move into live trees nearby and will not attack dead, previously infested trees.

What to Do Next

After MPB infests a tree, there is really only one best practice: Remove the tree. Landowners can either haul the tree out or chip it in place. Just remember, if you haul the infested wood away, make sure you take it outside of the forest, to a site at least 1 mile from susceptible pines.

To help prevent future infestations of MPB, landowners should give their trees extra water.  Douglas and Elbert counties have experienced extended drought for the past several years. Follow these late spring watering tips:

  • Water when it’s warm. The best time for late spring watering is on days when snow has melted and the temperature is above 40 degrees.
  • Water a wide area. Tree root systems may spread much wider than the height of the tree and the spread of the crown, with most absorbing roots in the top foot of soil and often far from the trunk. Apply water to soak the entire area underneath the full span of a tree’s branches.
  • Water slowly. To ensure deep penetration, use a drip or soaker hose on a low setting (or soft spray wand) to apply water slowly to the full area at the rate of 10 gallons per inch of tree diameter. That equates to about 40 minutes of watering with a soaker hose for a young tree with a trunk 2 inches in diameter and 120 minutes for a more mature tree with a trunk diameter of 6 inches.
  • Retain mulch. To retain soil moisture and save water, apply 4 inches of organic mulch onto bare soil within 2 to 3 feet from the base of the trunk, but not directly against the trunk.
  • Repeat as necessary. Until spring precipitation arrives, be sure to continue watering every few weeks during periods of warm temperatures when there is no snow on the ground.

About Mountain Pine Beetles

Mountain pine beetles (Dendroctonus ponderosae) are native insects to Colorado. In reasonable numbers, they provide important functions in forests. They can engineer natural forest thinning, killing weak or sick trees, leaving space and nutrients for healthy trees and other organisms. However, forests that are stressed from drought, fire damage or over-crowding allow MPB to thrive and increase their populations exponentially. Healthy, well managed forests are more resistant to MPB outbreaks. 

Contact your local Colorado State Forest Service Field Office with questions about the trees on your property.