Spruce and Larch Bud Moths

Bud moth larvae, Zeiraphera spp., have historically affected white and Lutz spruce stands in south-central Alaska. They will, however, attack Sitka spruce and larch (tamarack) wherever the host occurs in Alaska. Sitka spruce near Dutch Harbor and Unalaska in the Aleutian Islands and tamarack stands in interior Alaska (Figure 1) have been periodically infested. Black spruce is seldom attacked. There are two or more bud moth species with similar behaviors and life histories that cause most of the damage. Although tree damage is not usually severe, the effects from bud moth feeding are unsightly, and can be alarming to homeowners and land managers. This brochure will familiarize homeowners and land managers with the bud moth and provide guidelines for protecting and reducing damage to host plants.

life History

Adult bud moths are small, inconspicuous, gray- to brown-mottled moths with a wingspread of about 1/2 inch (Figure 2). Adult moths are commonly found flying from late June through July. During daylight hours they are usually found on the lower foliage of host trees. Adult moths become active at dusk. Their nocturnal flight activity is limited in distance and duration and is primarily restricted to the upper crown.

Female bud moths lay eggs from late June to mid-July beneath bark scales, on cones, and in the axes of twigs and branches. The spruce species lay a cluster of 1-7 eggs; the larch species lay eggs singly. Eggs are creamy-yellow when laid and gradually turn orange within a week. The bud moth overwinters as an egg and first instar larvae emerge from early May to early June. Larvae will emerge with warmer temperatures and bud burst, but this will vary throughout the range of the host.

Larvae immediately find a suitable bud, bore under the budcap, and begin feeding within the bud. As feeding progresses, larvae characteristically attach the budcap to the bud with silk (Figure 3). Often, more than one larva feed within a bud. As the bud expands, larvae feed on the new needles; as larval size increases (about 1/2 inch long) (Figure 4), feeding increases until most of the new needles within a bud are consumed. Larvae of some species of bud moth feed on the new needles along the terminal portion of a branch, whereas other species feed within one bud throughout the entire larval stage. Larvae feed from 3 to 6 weeks depending on the species of bud moth. When larval development is completed, larvae leave the foliage and drop to the ground on silken threads. They construct cocoons from pieces of moss, dead needles, soil, and any other organic material on the forest floor. The pupal stage lasts from 18 days to 3 weeks and new adults emerge as early as mid-June. There is one generation per year.

Damage

The bud moth is not considered a major economic forest pest. Damage is usually not serious and there is little tree mortality. Larvae feed exclusively on new foliage and severe infestations may cause reduced growth and multiple and deformed terminal and lateral branches (Cover photo). In many cases, the branch curls as it elongates usually towards the injured side where larvae have scarred the shoot tissue. Deep scarring makes the shoots fragile and susceptible to breakage. Bud moth damage can also predispose the tree to attack by bark and wood boring beetles and decay fungi.

Guidelines for Reducing Damage

Bud moth damage is rarely severe and suppression is not usually warranted. Trees in urban areas, however, may be more susceptible to bud moth attack, and heavy larval feeding can reduce their aesthetic value. In order to protect ornamental spruce, the following growing conditions should be provided for the tree to withstand periodic heavy defoliation:

• Care should be taken to avoid damaging the trunk and roots, altering the drainage patterns, and severely compacting the soil.
• Trees should receive adequate water throughout the growing season to avoid moisture stress.
• Spring fertilization helps promote tree vigor and helps minimize the effects of bud moth infestation. The USDA Cooperative Extension Service recommends from one to two pounds of fertilizer per inch of tree diameter. Fertilizer is applied in holes 8-10 inches deep in a series of concentric rings starting about 2 feet from the trunk and extending to a few feet beyond the dripline.
• Raking and removing litter beneath a heavily infested tree at the end of June will destroy and/or remove the pupae and thus reduce the subsequent bud moth generation.

If ornamental spruce has shown signs of heavy bud moth feeding for a few years, the following chemical treatment may be warranted:

• Insecticides should be applied to new buds from late May to mid-June when bud moth larvae are beginning to feed on expanding new growth. Check with your local Alaska Cooperative Extension Service for those insecticides, which are registered for control of bud moths.

CAUTION: Pesticides can be injurious to humans, domestic animals, desirable plants, and fish or other wildlife-if they are not handled or applied properly. Use all pesticides selectively and carefully. Follow recommended practices for disposal of surplus pesticides and pesticide containers. Mention of a pesticide in this publication does not constitute a recommendation for use by the USDA, nor does it imply registration of a product under the Federal Insecticide, Fungicide, and Rodenticide Act, as amended. Mention of a proprietary product does not constitute an endorsement by the USDA.

Spruce and larch Bud Moths

by Edward H. Holsten, Research Entomologist, USDA Forest Service, Alaska Region, State and Private Forestry

Additional information on this insect can be obtained from your local University of Alaska Cooperative Extension Service office, Alaska Division of Forestry office, or from:

Forest Health Protection
State and Private Forestry
USDA Forest Service
2770 Sherwood Lane, Suite 2A
Juneau, Alaska 99801-8545
Phone: (907) 586-8811

Forest Health Protection
State and Private Forestry
USDA Forest Service
3301 "C" Street, Suite 202
Anchorage, Alaska 99503
Phone: (907) 743-9455