Moth outbreak reported near Driggs

DRIGGS, Idaho (KIFI/KIDK)-The Caribou-Targhee National Forest is reporting an outbreak of Douglas-fir Tussock Moths.   The insect was found west of Driggs, on private lands near the Big Hole Mountains. 

The hotspot is part of a larger outbreak occurring throughout much of southern Idaho.

The defoliation caused by the tree-damaging caterpillar is seen as the reddish, half-chewed needles concentrated in the tops of trees.  It is most visible in mid-to-late August.  

While the trees can recover, even from heavy defoliation, those repeatedly defoliated of 90% or more of their needles have a high probability of dying.

“Many trees may look dead due to their red needles,” said Russ Oakes, Targhee Zone Silviculturist, “However, typically they are not dead and should not be cut for firewood. A good rule of thumb is if the tree has any green needles, do not cut.” 

Forest officials said Tussock moth populations began to increase in 2017.  The outbreaks usually last 3-4 years and subside when natural enemies, like a virus specific to the caterpillar, or parasitic wasps “crash the outbreak.”  This is estimated to be year 3 of the outbreak near Driggs.  USDA said natural controls are often the most appropriate control.  

Humans can be affected.

People visiting areas with heavy defoliation and lots of caterpillars or eggs should use caution.   The caterpillar’s long hairs may cause allergic reactions during August and September when they are peaking.   A rash called “tussockosis” can persist for hours or weeks.

For most people, a topical over-the-counter treatment can treat allergic symptoms, but people with severe reactions should seek medical attention.

You can learn more about the insect here.