Spruce budworms are making a return to Cook County

 

As unwelcome as they are, the eastern spruce budworm has returned to Cook County.

While large scale outbreaks of these pests occur in eastern Canada provinces and northern New England every 30 to 40 years, the budworm has been observed in Minnesota every year since 1954.

The larvae have worked their way through Lake County and last week were found in Schroeder and are steadily munching their way east.

These budworm’s feed mainly on balsam fir and spruce.

Starting at the tops of trees, these destructive pests eat this year’s current needles. If an outbreak is big enough, these larvae will feed on older needles and eat staminate (male) flowers and cones. Sometimes these larvae will destroy all of the cones.

The damage done to trees is most noticeable in the fall when the trees lose their dead needles, and the trees are grey in color.

If the spruce budworm infestation lasts only one year the trees can usually recover. However, if the defoliation occurs over a second year or longer, trees are much more susceptible to attacks by other insects and disease.

In Minnesota, management strategies include commercially thinning healthy stands of trees to retain trees with a greater than forty percent live crow ratio.

Trees in yards can be treated with pesticides but that is an expensive option and not suitable for forests. Dead and dying trees need to be removed before they become a fire hazard that threatens forests and homes and businesses.

The Minnesota Department of Natural Resources estimates that 94,500 acres of Minnesota forest from 2010 to 2014 were defoliated by these eastern budworms.

According to research conducted by Canadian Forest Service scientists, “adult moths’ mate and lay eggs in clusters of 10-150 on the needles of host trees in July and August. Newly hatched larvae spin cocoons in protected areas on the host tree where they spend the winter. In the spring, larvae emerge and start feeding on new foliage using the needles to build a silken shelter to protect themselves from predators.

Defoliation is most noticeable in late June when larvae have completed most of their feeding. Budworm moths emerge for pupae in July/August and lay eggs on the foliage to complete their life cycle.

Canada is forming a Spruce Budworm Intervention Strategy (EIS) to come up with a management approach that could help avoid large spruce budworm outbreaks and the loss of timber associated with those outbreaks.