Forest & Grassland Health

Generalist Defoliators Common in Alaska

Ghost looper- Epirrita undulata (Harrison)  
Great brown dart- Eurois astricta Morrison
Bruce spanworm- Operophtera bruceata (Hulst) 
Rusty tussock moth- Orgyia antiqua (L.)  
Speckled green fruitworm- Orthosia hibisci (Gueneé) 
Spear-marked black moth- Rheumaptera hastata (L.) 
Battered sallow moth- Sunira verberata (Smith) 

Photos

Click on the image for a larger version.

Sunira verberata defoliating aspen and other trees in Cooper Landing

Battered sallow moth defoliating aspen and other trees in Cooper Landing

Balsam Poplar Leaf-Folding Sawfly

Balsam Poplar Leaf-Folding Sawfly

Birch aphids and damage

Birch aphids and damage

Caterpillar Eurois astricta feeding on a willowin Glacier Bay National Park

Great brown dart feeding on willow in Glacier Bay National Park

 

Current Status (2020 Update)

Battered Sallow Moth Sunira verberata (Smith) 

Reports were received in late May and early June of caterpillars feeding on aspen in the Sterling area, as well as along the Marsh Lake Trail in the Kenai National Wildlife refuge. Additionally, on June 18, areas of intense hardwood defoliation were found along Juneau Creek Road just west of Cooper Landing. Quaking aspen were defoliated the most but birch, willow, black cottonwood, wild rose, highbush cranberry, and russet buffaloberry were also impacted. 

Balsam Poplar Leaf-Folding Sawfly​ Phyllocolpa excavata (Marlatt) 

Leaf-folding in seedling- and sapling-sized balsam poplar and black cottonwood was observed in many areas in Interior Alaska (Elliot Highway roadside sites from Minto and Livengood, south along the Richardson and Alaska Highways to Tok, on Chena Hot Springs Road) and at one site in Southcentral Alaska, near McCarthy. Both damage and the causal agent were observed. Prior to 2020, FHP observed similar damage in balsam poplar seen at the Vor Lake seaplane base in Bettles in 2018; however, no damage agent was found.  

Birch Aphid Euceraphis betulae (Koch) 

Birch aphid is common throughout the state and heavy damage is occasionally documented in Southcentral and Interior Alaska. In the mid-1970s, 500,000 acres of damaged birch with heavy aphid populations recorded in the Palmer and Chickaloon areas. More recently, smaller defoliation events presumed to be aphid-caused were observed in Slana in 2014 and at Sevenmile Lake in 2017. In the spring of 2020, aphid populations increased in some Interior birch stands and early season feeding on buds caused failed leaf production or distorted, discolored, and tattered leaves and premature leaf drop.  

In late May, FHP conducted a site visit following several reports of extensive birch defoliation along the Richardson Highway in the Birch Lake area. Birch foliage appeared tattered and discolored, consistent with early season aphid feeding. This damage was mostly concentrated in the upper crowns. In late June, several stands of birch along Johnson Road in Salcha were observed during ground surveys with tattered and discolored foliage and defoliated tops consistent with early season aphid feeding. Damage ranged from minor to complete birch defoliation with some minor impacts to alder species. Large populations of birch aphids were also present on the undersides of most accessible birch and alder leaves. Birch aphid activity was also common around Fairbanks and all roads throughout the Interior, as well as in the Copper River Valley, along Turnagain Arm, and near Sterling. Most birch aphids observed were at trace to moderate levels, with the exception of the heavily defoliated areas mentioned above. Several birch trees at each site re-flushed in small sporadic clumps, though no wholesale re-flush of defoliated trees was seen. Over 850 acres of heavy birch defoliation was mapped along the Richardson Highway near Birch Lake and along Johnson Road in Salcha during the site visits described above. Birch aphid was confirmed as the causal agent on over 200 of those acres during ground surveys of accessible stands where  moderate to heavy populations were present.  

Symptoms, Life History & Impacts of Common Defoliators

The rusty tussock moth larva is a dark, hairy caterpillar adorned with four yellow “tussocks” of hair along the back. The caterpillars are generalist feeders on a variety of shrubs and trees, including aspen, willow, birch, cherry, and blueberry. The adult females are flightless, and the males are a rusty brown color with a white spot on each forewing. The adults lay eggs before winter, and caterpillars emerge from the eggs in the spring. High populations of these caterpillars can cause substantial defoliation. This moth is found throughout Alaska.  

The great brown dart larvae feed on aspen, cottonwood, alder, and birch in Southeast Alaska. Not much is known about this species, but larvae feed in spring and adults fly in late summer/early fall. The adults are marked with mottled grey/brown forewings. In June 2019, a local outbreak of the caterpillars was observed defoliating trees in Glacier Bay National Park, however, there was evidence that the caterpillars were infected with a baculovirus. By August the trees had re-foliated and recovered from the damage. 

The speckled green fruitworm larva is another generalist hardwood caterpillar that feeds on aspen, willow, birch, cherry, apple, and alder species throughout the state. The larvae is large, smooth caterpillar that is green in color with light stripes down the sides. The larvae overwinter as pupae in the soil, and adults emerge very early in spring (March – April). This is another caterpillar that can cause substantial local defoliation.  

The battered sallow moth is similar to the speckled green fruitworm, however, adults fly in late summer/early fall, rather than spring. The larvae are darker in color than the speckled green fruitworm, but also are generalist hardwood defoliators. In 2017, considerable hardwood defoliation was found along the Richardson Highway between Valdez and Glennallen. The battered sallow moth larvae (identified by DNA analysis) were severely defoliating alder, willow, balsam poplar, shrubs and some herbaceous species. 

GUIDELINES FOR REDUCING DAMAGE: 

Urban owners of ornamental hardwood trees and shrubs should insure the best possible growing conditions so that the trees can withstand periodic defoliation. Care should be taken to avoid injuring the roots with mechanical devices or soil compaction. To avoid moisture stress, trees should receive adequate water throughout the growing season.  

Content prepared by Alexandria Wenninger, Biological Technician, Forest Health Protection, alexandria.wenninger@usda.gov

For more information contact: Elizabeth Graham, PhD.  Forest Entomologist, Forest Health Protection, elizabeth.e.graham@usda.gov

 





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