Defoliation of white spruce by spruce budworm larvae is a fact of life again this summer in Region I. Larval surveys of white spruce stands in Becker, Hubbard, Beltrami and Cass Counties were carried out and completed by June 26th. Stands defoliated for each of the past five to six years were fed on again this summer. Aerial surveys carried out in July of 1996 detected spruce defoliation in Cass County just east of Cass Lake. These stands were sampled for the first time and results confirm that new infestations have taken place on spruce plantations that are twenty to thirty years old. Results of surveys indicate that defoliation is increasing in geographical distribution in Region I and also into white spruce stands situated between Region I & Region II in the Chippewa National Forest.
This defoliator of spruce and balsam continues to spread to plantations in central Minnesota. By June 25th, budworms had nearly completed feeding and causing damage to shoots, needles and next year's buds. Surveys earlier in June in northeastern and central Minnesota revealed that numbers of budworm had increased in several areas.
Fortunately, spruce and balsam can tolerate several years of heavy budworm damage before top kill and entire tree death occurs.
Silvicultural tools to manage budworm impact include harvesting of mature trees, breaking up large tracts of host trees and thinning of closely planted trees. Chemical control is most effective on isolated stands or shelterbelts of white spruce. Insecticides containing the bacteria, Bacillus thuringiensis, are recommended and sold as Attack, Bactospeine, Biobit, BT, Biospray, Dipel, Foray, Javelin, or Thuricide. Chemical control should be aimed at very young budworms next spring when the buds are just loosing their bud caps.
Egg mass surveys will be done later during the summer and summarized in the fall Newsletter and Annual Report.