Pine loopers may loop back for second year of devastating defoliation

By: 
Nathan Steele

Last summer, property owners near Pringle began to notice the disappearance of needles from surrounding pine trees, making the ridge along Beaver Creek appear gray and bare.  The cause of the defoliation was a recent outbreak of pine loopers, a moth that feeds exclusively on pine needles during its larval caterpillar stage. Pine loopers are native to the Black Hills, but usually appear in fewer numbers, affecting only small pockets of forest. Sometimes, however, the population explodes into an outbreak, lasting one or two years, typically.
“Periodically, for reasons not clearly understood, populations increase leading to defoliation in isolated areas. This is currently happening near Pringle. This outbreak, which started last year, is like previous outbreaks in the Black Hills from the early 2000s and 1970s,” said Dr. John Ball, a South Dakota State University Extension Forestry Specialist & South Dakota Department of Agriculture and Natural Resources Forest Health Specialist. Generally, there are 20-30 years between outbreaks for a given location.
“Although there may be additional defoliation this year, based on past outbreaks, we do not anticipate this outbreak continuing into a third year,” said Ball.
Last year’s defoliation, saw nearly every tree stripped of its foliage on the ridge along Beaver Creek near Pringle. The pines have been recovering as expected, but the threat of a second round of defoliation could be reason for concern. After a recent survey of pine looper pupae in the area, work will be done to monitor adult populations.  The survey revealed three to five live pine looper pupae per square inch of litter in the impacted area—more than usual.
“These results are elevated compared to normal conditions and indicate larvae numbers will also be high. This could mean a second year of defoliation in the impacted area,” said Ball.
 Healthy pines can handle one year of defoliation, but after months of drought conditions, most of the pine trees are not healthy. Recent precipitation is only just beginning to push the area out of drought status. Most of Custer County is currently categorized as abnormally dry, and the westernmost part of the county is still in moderate drought. For this reason, a second round of defoliation could prove fatal to those pines.
This month, Ball and the team will begin to set up light traps to get an idea of  what size the adult population will be. They will then use that data to determine how much defoliation can be expected or to document declining populations.
After they get an idea of how many adult moths are in the area, notice can be given to homeowners and the best course of action can be determined. If the population is high, landowners  may want to treat their pines with an insecticide in late July—just after eggs hatch—to kill the caterpillars before they cause too much defoliation.
“Right now, the focus is on monitoring. If monitoring predicts a second year of defoliation, landowners will have time to treat high-value pine trees,” said Ball.

 

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