Western Spruce Budworm Control in the Flathead Valley
Introduction
Northwest Management Inc. (NMI) a natural resources consulting company with offices in Montana, Idaho and Washington is coordinating western spruce budworm control work on private property throughout the Flathead Valley and Montana. The control work will commence towards the end of June to mid-July.
Western spruce budworm is an insect pest which defoliates Douglas-fir, Engelmann spruce, subalpine fir, grand fir, and western larch trees. Tree damage associated with budworm defoliation includes growth loss, top-kill, deformity, reduced seed production and tree mortality. Larger diameter trees that survive major budworm outbreaks are left in a weakened condition and may later be killed by bark beetles. It usually takes three-five years of repeated tree defoliation to cause top kill, reduce growth and tree mortality. Seedling and sapling-sized trees are most likely to suffer severe damage and mortality
Misconceptions
There is a misconception that you do not need to respond to a budworm outbreak because it’s a naturally occurring event that usually lasts 2-3 years and the trees will recover over time. We are currently witnessing budworm outbreaks that are lasting upwards of ten years and are causing extensive tree mortality throughout Montana. Spraying for western spruce budworm kills the feeding larval caterpillars and maintains green foliage for healthier trees. Trees that have been repeatedly defoliated from budworm are being killed by bark beetles and a variety of abiotic factors. Northwest Management Inc. (NMI) has coordinated the spraying of over 18,000 acres in Montana since 2008 on forested properties ranging from 1 acre to over 800 acres.
What to look for:
When tree shoot growth begins in May-June budworm larvae (small caterpillars) web together adjacent shoots. Budworm larvae then start feeding on the new foliage in mid to late June. During July reddish brown branch tips will give trees a scorched appearance. The upper portion of the tree crown may appear bare or thin. Older larvae have dark heads and an olive-brown body with whitish spots. Pupal cases are often attached to damaged shoots. Orange to gray-brown moths less than an inch acrossare abundant in late July and August during an outbreak.
Control
Natural controls include ants and birds which eat budworm larvae. Leaving woody debris on the ground for ants and snags as nesting sites for birds can help sustain populations of these predators. Other natural controls are believed to include cold, wet spring weather; viral pathogens, and lack of food following subsequent years of infestation.
Silvicultural practices include maintaining or increasing tree diversity in vulnerable stands (increase the relative abundance of non-host tree species), thinning from below to create single story forest stand structures, and thinning to reduce inter-competition between trees and to increase the vigor of retention trees.
Insecticides or biological larvacides are most effective when applied as larvae are actively feeding on new foliage in June or July. For large outbreaks aerial applications of Bacillus thuringensis(Trade name- Foray or Bt) a naturally occurring bacterium and the chemical insecticide Tebufenozide (Trade name –Mimic)) an insect growth regulator are generally recommended. Ground based applications of Mimic and Bt can be effective on smaller trees. Bt is a is a biological larvicide host specific to feeding Lepidoptera (caterpillars). Bt is commonly used and certified for use in organic farming. It poses no risk to any other species besides feeding caterpillars.
Figure 1 Spraying a Big Sky Homeowners Association
To be most effective the Bt needs to be applied with the emergence of new foliage and presence of feeding larvae. NMI foresters monitor the budworm development to determine the appropriate time to spray which is typically late-June to mid-July.
Bt must be eaten by the larvae to cause mortality. A protein crystal formed by the bacterium carries a toxin which is released in the gut of the larvae. When Bt is ingested the toxin is released and the midgut wall is destroyed and the larvae stops feeding. The bacterium enters the blood of the insect causing full scale infection and death of the insect within 3-5 days. As soon as the budworm ingests the bacterium they stop feeding.
Mimic is a highly selective insect growth regulator insecticide used to control Lepidoptera pests in forests and food crops. It has a novel mode of action in that it imitates the action of the insect molting hormone, ecdysone. Lepidoptera larvae cease to feed within hours of exposure and then undergo a lethal unsuccessful molt. Mimic has an excellent environmental andsafety record and was the recipient of the Presidential Green Chemistry Award.
The vast majority of Northwest Managements Inc. clients elect to sprayBt because its naturally occurring and is certified for use on organic farms.
Aerial application of Bt:
Figure 2 Spraying Bt in residential area of Big Sky
Aerial application can be accomplished with fixed wing aircraft or helicopters. Fixed wing aircraft are generally less expensive if a landing strip can be located in close proximity to the project area. NMI foresters create maps and aerial photos of properties to determine the amount of forested acres that will be sprayed. NMI foresters also monitor the properties to insure that the larval caterpillars are the appropriate size before initiating the spray program. The application must be timed with the emergence of new foliage and presence of feeding larvae to be effective. Generally results are decreased level of defoliation but not complete elimination. Reapplication of chemical and biological treatments may be required during the duration of the spruce budworm outbreak. Historically, outbreaks in Montana have duration of 2-5 years. The cost to spray is approximately $60 to $90 an acre depending upon the size of the tract, continuity and the total amount of acres sprayed from a staging area.
Figure 3 Tree mortality caused by western spruce budworm northwest of Helena
Contact
If you are interested in having your property sprayed or assessed please contact us.
Jim Cancroft
Senior Forester/Wildlife Biologist
Northwest Management Inc. 406-442-7555 office
406-544-8489 cell