Spruce Budworm
Order: Lepidoptera
Family: Tortricidae
Latin Name: Choristoneura fumiferana (Clemens)
Common Names: Spruce Budworm, Eastern Spruce Budworm
Introduction
The spruce budworm has caused more damage to Nova Scotian softwood forests than any other insect. Overmature balsam fir is the preferred host and acts as a flash point for rapid population buildup. Populations tend to increase steadily and spread to younger trees. Feeding takes place on the top third of the tree on new shoots. High populations will result in repeated loss of all new foliage which will kill the trees within 3 - 4 years. In dry, hot conditions, these trees can be fuel for forest fires.
Life History
In late August or September, the eggs hatch, the larvae molt, and overwinter in the second instar. In late April or early May, the larvae (3 mm long) emerge from their hibernacula and begin to feed, mining the needles and buds. A week later they move to feed on the closed buds and any developing shoots. The larvae are fully grown within five weeks. They have black heads and a dark brown body, 18 - 24 mm long. They pupate on the foliage and the adult moths emerge in July to lay eggs which hatch in 2 - 3 weeks. The adults are dull grey with a wingspan of 20 mm.
Damage Symptoms
Defoliated trees over large areas with red foliage; particularly the new foliage on the upper third of the tree.
Early Intervention Strategy
The Early Intervention Strategy for the eastern spruce budworm has been developed as a proactive approach to managing budworm outbreaks by targeting and controlling small, emerging populations before they cause widespread damage to our forests. By targeting these “hot spots”, the strategy aims to interrupt or slow the progression of potential outbreaks and prevent them from developing into major events by using tools such as intensive monitoring, early detection of low-level increases of populations and targeted insecticide applications. Early intervention is important to help reduce the impact on our forests including increased risk of wildfire.
Control Options
Harvest stands of overmature fir and spruce to remove potential population build up sites. Biological control products are recommended for large forested areas. These will not interfere with naturally occurring parasites and diseases that help control budworm populations.
Btk Treatment
Btk treatment contains spores of a bacterium that occurs naturally on dead or decaying matter on plants and in soils. It is a targeted insecticide that only affects the larvae of moths and butterflies. There are practically no impacts to nontarget species due to Btks need of high alkaline environments. All other species groups have acidic stomachs, which do not activate Btk spores and instead break them down, rendering it ineffective and harmless.
Following application, Btk remains active on the treated foliage for only 2-4 days, rapidly degrading as a result of sunlight and microbial activity. It breaks down rapidly in both soil and water and does not accumulate in the environment. The treatment has no direct or indirect impacts for birds, mammals (including humans) or other organisms that may feed on treated larvae as a food source.