Not in Tents, Just Intense

Winter is not a season when people think about tents, except maybe to be glad they do not 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 the eastern-tent caterpillar and other species of tent caterpillars. The tent-less lifestyle of forest-tent caterpillars 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 dense populations. The damage occurs within 6-8 weeks in May and June.

Trees typically grow a new set of leaves by mid- to late July, but at great cost in terms of lost starch 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 defoliations are more likely to lead to tree mortality.

Foresters and woodlot owners may want to learn more about tents 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. And since the female FTC moth frequently lays eggs in maples, outbreaks often show up early in maple stands. This past year in parts of northern NY from the Vermont border west to Jefferson and Lewis Counties, localized but severe outbreaks of forest-tent caterpillars reportedly stripped close to 200,000 acres, primarily sugar maples. Early indications are that the infestation will be more widespread in 2018.

One troubling aspect of the 2017 FTC defoliation is that the vast majority of defoliated maples did not grow any new leaves, although in a few cases they refoliated to a small degree. There does not appear to be recorded precedent for this. Most foresters agree that the phenomenon is a result of the 2016 drought, which stressed trees to such an extent that they were not strong enough to push out a new flush of leaves. In an even more bizarre twist, some maples on south-facing slopes did refoliate, but in early to mid-October. The new growth was still in process when a hard freeze killed the leaves along with the new buds.

Maple producers in FTC-affected areas should expect sap-sugar concentrations to be a fraction of a percent, in contrast to normal concentrations between 2 and 3 percent. According to Cornell Extension Forester Peter Smallidge, operators 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.

Whether or not a woodlot owner or maple producer had FTC damage in 2017, the St. Lawrence County Maple Expo held from 8AM to 3PM on Saturday, January 27, 2018 at the Gouverneur High School can help answer questions about FTC. The FTC segment of the program will cover how to scout for egg masses, and to interpret the numbers and make projections, and treatment thresholds and other considerations. The Expo will also treat many other key topics including Cornell Maple Research Update, Maple Tubing Systems, Regenerating a Sugarbush, Marketing, and more.

For more information on the 2018 Expo, go to or call (315) 379-9192.

If you miss the Expo, you can learn more about forest-tent caterpillars by contacting your local Cornell Cooperative Extension office.

Views: 82

Comment by Paul J Hetzler on January 26, 2018 at 2:33am
Also, according to a large Clinton County maple producer who called this week, there is "not the slightest evidence of tree wound response" on 2017's tap holes in the 1,000 acres of sugar bush that remained barren of leaves (post-FTC) all last year.
Comment by Paul J Hetzler on January 26, 2018 at 2:41pm

For a list of about 40 tree-related articles, visit , where nature and humor collide. Amicably for the most part. Click on the "Natural Resources Essays" heading and then scroll down to the "Trees" section. 

Comment by Brett Chedzoy on January 26, 2018 at 11:18pm


Any good short videos or picture guides on how to scout for FTC egg masses this time of the year, including "acceptable" levels?

Comment by Paul J Hetzler on January 27, 2018 at 8:51am

The DEC has a great document:

also VT:

Not sure the copy/paste worked right...


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