Occurrence of insect and disease pests on young-growth Sitka spruce and western hemlock in southeastern Alaska.

Abstract

Insects and diseases were surveyed in 16 even-aged, young-growth stands of Sitka spruce (Picea sitchensis (Bong.) Carr.) and western hemlock (Tsuga heterophylla (Raf.) Sarg.) in southeastern Alaska. Stand ages ranged from 17 to 27 years in nine thinned stands and from 12 to 22 years in seven unthinned stands. All stands appeared healthy. Although some organisms with damage potential were observed, no pests occurred at levels likely to cause damage. Insects recorded on spruce included a Zeiraphera sp. shoot moth (the first record of this insect in southeastern Alaska), a Dioryctria sp. moth, and a Pineus sp. aphid. Fungi that cause spruce diseases included Lophodermium picea (needle cast), Chrysomyxa ledicola (needle rust), and Discocainia treleasei and Heliotium resinicola in cankers. Insects on hemlock included Pseudohylesinus tsugae bark beetles, which occurred more frequently in thinned stands and on trees larger than 3 inches in diameter at breast height, and the adelgid, Aldeges tsugae. Diseases on hemlock included needle rust caused by Pucciniastrum vaccinii and dwarf mistletoe (Arceuthobium tsugense). Sawflies (Neodiprion spp.), geometrid moths (including Melanolophia imitata), blackheaded budworm (Acleris gloverana), and the shoot blight fungus, Sirococcus strobilinus, appeared on both spruce and hemlock. Armillaria sp. occurred in 39 percent of 165 hemlock stumps and 36 percent of 165 spruce stumps following thinning and was more common in hemlock stumps from stands thinned 5-6 years earlier than in those thinned 3-4 years earlier. Fomes annosus was found in only 2 percent of the spruce stumps and in no hemlock stumps.