Not in Tents, Just Intense

Submitted by Paul Hetzler, Horticulture and Natural Resources Educator, CCE St. Lawrence County

Winter is not the season when people think about tents, except maybe to be glad they don’t live in one. I do have friends who love winter camping, and the fact they have never extended an invitation is evidence of how much they value our friendship.

Oddly enough, winter is a crucial time to look for signs of forest-tent caterpillars (FTC). In spite of their name, FTC do not weave a silken tent-like nest as do their close cousins the eastern tent caterpillar (ETC). The tent-less lifestyle of FTC makes it harder to spot outbreaks in spring.

Records indicate the population of this native pest spikes at irregular intervals, generally between 6 and 20 years apart, at which time they can cause near-total defoliation at high populations. The damage occurs within 5-6 weeks in May and June. Trees grow a new set of leaves by mid- to late July, but at great cost in terms of lost energy reserves, and afterward they are more vulnerable to other pests and diseases. The problem is compounded by the fact FTC outbreaks historically last 3 years on average. Successive years of defoliation are more likely to cause tree mortality.

Foresters and woodlot owners may want to learn more about tent-cats this winter, but maple producers should pay special attention to the situation, as sugar maples, which leaf-out earlier than oaks and ash, are a preferred food for the FTC, possibly their favorite. And since the female FTC moth primarily lays eggs in maples, outbreaks begin early in maple stands.

This past year, parts of northern NY from the Vermont border all the way across to Jefferson and Lewis Counties saw localized but severe outbreaks of forest-tent caterpillars. The New York State Department of Environmental Conservation (NYSDEC) has confirmed that at least 200,000 acres of NNY forest, predominantly sugar maple, were stripped bare.

The most troubling aspect of last year’s defoliation is that nearly all affected maples failed to grow new leaves, though in a few cases some did to a small degree. This is unprecedented. Foresters agree the phenomenon is related to the 2016 drought, when record-setting low soil moisture damaged tree root systems so badly, trees were too weak to push out a flush of new leaves following the 2017 FTC attack. It is normal to assume tree roots dive deep in search of water, but a lack of oxygen at depth limits them. In fact, 90% of tree roots are in the upper 10” of soil, with 98% in the top 18 inches. In long dry spells, tree roots die back, starting with the network of fine absorbing (“feeder”) roots.

Maple producers in FTC-affected areas should expect sap-sugar concentrations to be a fraction of a percent this season, in contrast to normal concentrations between 2 and 3 percent. According to Cornell Extension Forester Peter Smallidge, those with reverse-osmosis capability may still get a substantial crop in 2018. Some small producers with FTC damage, however, are opting not to harvest sap this season, partly for financial reasons, but also to spare their maples further stress.

Maria MoskaLee, Forest Health Specialist & Field Crew Supervisor with NYSDEC’s Forest Health Unit, spot-checked in northern NY this fall for FTC egg masses, which is a way to tell how far the pest may have spread, and how severe an infestation is likely to be. In St. Lawrence County, each of the 10 survey locations had egg masses present in sufficient numbers to cause outbreaks at those places. Maria told me that in general, the FTC outbreak will probably be severe again across NNY, and that it has spread significantly beyond 2017 boundaries.

Weather is the FTC’s biggest enemy. Their eggs survive extreme cold, but winter thaws are bad. Foresters have their fingers crossed that this winter’s freeze-thaw trend continues. Cool springs are even more deadly for tent-cats. At 55F and below, their digestive tract shuts down. They are able to feed, but if it remains cool, they will starve to death with full bellies.

Whether or not a woodlot owner or maple producer had any forest-tent caterpillars in 2017, Cornell Cooperative Extension and the NYSDEC want to encourage landowners to look for FTC this winter. Naja Kraus of the NYSDEC has written clear and detailed instructions on surveying for FTC. Entitled “Forest Tent Caterpillar Egg Mass Sampling,” you can find it at http://www.dec.ny.gov/docs/lands_forests_pdf/ftc01.pdf.

If you do not have access to a computer, call Cornell Cooperative Extension at (315) 379-9192 to have a copy mailed to you.