Field Guide     Pest Management     Budworms

Budworms

CROPS IMPACTED: Spruce trees, fir trees

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Family: Tortricidae

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About Budworms

Reproduction and Life Cycle

Budworms have one generation each year. A female moth will lay its eggs starting in July and continue into the beginning of August. They will place their eggs on the underside of the trees needles in bunches that can range anywhere from 2 to 60 eggs, placed in 2 overlapping rows. The adult will die shortly after. The eggs will take about 10 to 14 days to hatch; the budworm larvae will emerge and immediately spin their hibernacula, or silken cover. The larvae will enter the second instar stage of development and will stay in their sheltered cover throughout the winter. They emerge from their hibernacula early in May when the weather warms up and will continue to molt, feeding on tree shoots, unopened buds, and old needles. They will continue to feed for the next 5 weeks, going through a total of 6 to 7 instars. The majority of feeding occurs during the fifth and sixth instar. Adult budworms will then emerge as moths in the beginning of July to mate and lay eggs.

Budworm Identification and Habitat

Identification

An adult budworm can be identified by its 21 to 30mm wide wingspan, and their grey-brown colour. They also typically have forewings with silvery spots. The eggs an adult will lay are small, oval and light green in colour. Developed larvae are typically 22mm long with a brown head and a greenish-brown body. On the back of the body there are lightly coloured spots placed in rows. The pupa is approximately 12mm long, starting as a pale green and then later deepening to a reddish-brown colour.

Habitat

The spruce budworm is known to be one of the most detrimental pests to forests throughout North America. The larvae are the most destructive, and have the ability destroy thousands of hectares of spruce and fir trees if their population is high enough. They tend to prefer red and white spruce and balsam fir. At a modest level, the spruce budworm is a healthy contributor to the ecosystem; however, every 30 to 40 years a major outbreak tends to occur, which is when the damage is most apparent. These outbreaks can last several years, defoliating and killing the entire plant by the fifth year. The budworms tend to congregate at or near tree crowns, so when scouting for this pest, it is advised to look in this area first.

Budworm Management and Control Methods

Management

Often budworm populations are kept in-check by natural factors and predators, such as unfavorable weather conditions, spiders, birds, parasitoids and a lack of available food. Most of these predators will eat the larvae once winter has passed and the larvae emerge from their hibernacula’s. The parasitoids will place their eggs in the budworms pupae, or in with their eggs, which will effectively kill the budworm in this stage of development. However, when budworm populations rise too high, it is important to use an integrated management plan that incorporates both cultural and chemical control methods for the best results.

Cultural Control

When budworms continue to feed off of the same spruce and fir trees year after year, this decreases the trees robustness and strength, making it easier each year for the budworm larvae to create a greater amount of damage. By ensuring your trees are getting the nutrients they need to grow back strong each spring, water, thin out, and fertilize the trees. This can help the tree to withstand the larvae attacks.

Chemical Control

There are many insecticides available to control budworm populations. If a large area needs to be controlled, aerial sprays are often used. For these commercial operations, the insecticides available are Tebutinozide, and Bacillus thuringiensis. If spraying only a few trees around your house or in a small area, domestic products to use are dimethoate, carbaryl, acephate, permethrin, trichlorfon, and aminocarb. These chemical should be applied at the time when larvae are in the third or fourth instar, or when they are approximately 8mm in length. This is usually at the same time that shoots are opening. This will kill the larvae before they enter the most damaging fifth and sixth instars. Be sure to carefully read insecticide labels for cautions and proper application.

Latin / Alternative Budworm Names

  • • Choristoneura fumiferana

Sources

http://www.nrcan.gc.ca/science/video/11724

https://www.gov.mb.ca/conservation/forestry/pdf/health/spruce_budworm.pdf

http://bugguide.net/node/view/35699