Missing leaves & other notes
The case of the missing leaves
If there aren't any leaves on your aspen by the end of May is it just a late spring or could it be something more sinister? As was reported in the October issue, large aspen tortrix defoliated aspen near Duluth last spring. In the Thunderbay and Nipigon Districts of Ontario, tortrix caused close to 500,000 acres of defoliation.
The second instar larvae (caterpillars) emerge as the buds swell but before leaves emerge in the spring. They feed inside the swollen buds and large populations can completely consume all the leaves even before they emerge. People sometimes confuse the lack of leaves early in the spring with a late spring rather than
defoliation by the tortrix. Surviving leaves eventually unfold. The caterpillars then roll, fold and tie the leaves together and feed on them. Large amounts of silk are sometimes spun by tortrix caterpillars on trees and shrubs.
Outbreaks usually only last two to three years and are too short to cause any significant tree mortality. The last couple of times the large aspen tortrix started to build up in Minnesota, they seemed to have been run over or overtaken by FTC outbreaks.
The return of the forest tent caterpillar
It's too early in the process to declare the start of a full fledged outbreak. However, after being absent from most of the state since the early 1990's, the forest tent caterpillar appears to be attempting a comeback. Last year people in northeastern Minnesota started finding solitary caterpillars crawling across their driveways and sidewalks. There was a significant area of defoliation by the FTC on the east and southeast edge of Lake Mille Lacs. And last year in Canada, there were close to 300,000 acres of FTC defoliation in NW Ontario near Kenora, Dryden and Thunderbay. Last fall, a few FTC cocoons were found east of Ely and just south of International Falls. This winter, single egg masses were found on four of five plots surveyed east of Ely and near Duluth. Multiple egg masses were found on four of five plots surveyed near Lake Mille Lacs.
Is this is the start of an outbreak? It's probably too early to tell. It's like wondering last spring if Marc McGuire would break the home-run record. The signs seem to be there but it will depend on the weather and other factors that affect the FTC population. We could hope and pray for a really cold, wet spring that would kill off the population. The reality is that this year we'll start seeing larger areas of defoliation centered around localities FTC defoliation was observed last year. In NE Minnesota, it is likely there will be a few small areas of defoliation but it should not be very widespread or noticeable.
FTC does have some good points and some tangible benefits. So, when you think about FTC, don't get depressed-think BIRD FOOD.
FTC and the Gilchrist Lake Association in Pope County
A project review meeting was held Saturday April 17, 1999 to prepare for the mid-May spraying of forest tent caterpillars in the Gilchrist Lake area of Pope County. One time matching funds from a Community Forest Health Grant will help sponsor the control project using BT from a helicopter. DNR's involvement will focus on technical assistance, promoting educational materials, assisting in post spray evaluations and delineating woodlot management actions to increase stand vigor and species diversity.