SPRUCE BUDWORM IN MINNESOTA
The Eastern Spruce Budworm (SBW) is a native pest in Minnesota that follows a "boom and bust" population cycle of about 30-40 years. During the 6-8 year "boom" phase, it devours new growth on balsam fir and white spruce trees. The “boom” phase persists until most food sources are depleted, leading to extensive tree loss. The outbreak of spruce budworm in Minnesota is expected to last until about 2029.
SPRUCE BUDWORM LIFE CYCLE
Adult moths can travel up to 120 miles and lay hundreds of eggs in multiple locations. The eggs overwinter and emerge as larvae the following spring. The larvae prefer hot, dry summers, which is unfortunate, with regard to the changing precipitation caused by climate change. During the 6-8 year "boom" phase, SBW larvae devour new growth on balsam fir and white spruce trees. Since trees “prioritize” growth in their new branches, the loss of this investment is extremely harmful to the tree.
SPRUCE BUDWORM & FIRE
The aftermath of SBW infestations also includes a heightened risk of wildfires. Dead trees left behind serve as fuel on the forest floor, increasing both the likelihood and intensity of fires. Standing dead trees serve as "ladder fuel" that can ignite the canopy. In fact, the SBW is considered a major contributor to the 2021 Greenwood Fire in Minnesota, which burned nearly 30,000 acres and closed the Boundary Waters Canoe Area Wilderness for the first time since the drought of 1976.
WHEN WILL SPRUCE BUDWORM END ?
The “boom” phase of the SBW persists until most food sources are depleted and the population can no longer sustain itself, but not before leading to extensive tree loss. The previous SBW outbreak in Minnesota was in the 1980's, with a peak defoliation of about 440,000 acres in 1986. In 2023, SBW defoliated about 665,000 acres in Minnesota. The current outbreak of spruce budworm is expected to last through approximately 2029.
SBW IMPACT & CLIMATE CHANGE
Climate change exacerbates the Spruce Budworm (SBW) problem, as the trees are already stressed from heat and drought, and with weakened defenses, trees are more susceptible to insect infestations such as the SBW. Climate change is also expanding the geographical SBW range; warmer temperatures allow the SBW to persist in regions where they were less prevalent in the past. Further, climate change extends the growing season, allowing the “boom” phase of the SBW lifecycle to last longer due to warmer temperatures.
The emerald ash borer (EAB), an invasive pest originating from Asia, poses a severe threat to all ash tree species, including green ash, white ash, and black ash. First detected in Michigan in 2002 and then in Minnesota in 2009, EAB has impacted forests across the entire eastern half of the U.S.
The consensus among forestry experts is that EAB will destroy nearly all ash trees in the U.S., in both urban and forested areas, leading to significant, lasting changes in North American forests with substantial ecological, economic, and social impacts. Minnesota will not escape the fate of nearby states that have lost nearly all their ash trees.
EMERALD ASH BORER IN MINNESOTA
IT'S ONLY JUST BEGUN
EMERALD ASH BORER IS MOVING NORTH
Unfortunately, the northward movement of EAB threatens Minnesota's vast ash forests. Foresters initially hoped that the colder temperatures in northern Minnesota would deter EAB infestations, but the cold has only slowed the spread of the pest. EAB can tolerate temperatures down to -30°F in the winter, and our winters are just not getting as cold anymore.
Warming winters attributed to climate change are expected to exacerbate the issue in the coming years, making EAB an increasingly serious threat to Minnesota's ash tree populations. This situation necessitates proactive measures, such as planting new tree species, to mitigate the impact of EAB on forest ecosystems.
Minnesota is home to more than one billion ash trees, and EAB has only just begun to devour them. Numerous areas in the state are particularly vulnerable to EAB infestations, amplifying their devastating impact. For example, north central Minnesota is home to 1.2 million acres of black ash wetlands that are specifically suited to this tree species. This concentration of ash presents additional hurdles for forestry experts striving to contain EAB. Replanting these large areas with other species capable of thriving in wet locations is a significant challenge and will require the work of many individuals and organizations working together.
EARLY DETECTION OF EAB IS CRITICAL
Fifty-two counties in Minnesota are infected with EAB, and the Minnesota Department of Agriculture has instituted bans on transporting firewood to limit the spread. Early detection of EAB is key, as it allows for the treatment of some trees and helps slow the inevitable spread. If you notice higher levels of woodpecker activity in your area, this is a sign to investigate whether you have a new pest in the neighborhood. Rarely do individuals see the adult EAB, however. Instead, look for signs that the tree is struggling, such as yellowing or dropped leaves. Then check for the telltale galleries under the bark and the larvae within them.
EMERALD ASH BORER LIFE CYCLE AND IMPACT
Trees invaded by the emerald ash borer die within just a few years unless chemically treated.
A tree must have at least 70% of its canopy left for treatment to be effective. While it is feasible to treat ash trees infested with EAB in a private yard or in the city, this is not feasible in the vast areas of ash in northern Minnesota.
While ash trees can survive a light EAB invasion, a full infestation will lead to the death of the tree within 1-3 years of visible symptoms, such as the 1/8" “D” shaped exit holes. EAB has a 1–2 year life cycle and primarily lives underneath the bark, with the larvae creating tunnels or "galleries" that disrupt the tree's ability to transport water and nutrients.
