The Spruce Budworm in Minnesota |
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abundant bark beetle become established beetles or fungi black spruce break buds budworm attack budworm control budworm larvae budworm outbreaks budworm-susceptible Bureau of Entomology ceptible chestnut-sided warblers conifers Cook counties crop trees cultural operations cut of balsam danger of windthrow defoliated trees destroyed EFFECT OF BUDWORM EFFECTS OF DEFOLIATION eggs extensive areas feeding period fir and spruce fir or spruce fire hazard foliage growth hardwoods heart rot hibernation important increase insect insectivorous birds jack pine Koochiching LAKE COUNTY large number merchantable mixed stands moths natural succession needles northeastern Minnesota northern coniferous forests northern Minnesota one-tenth acre parasitic possible practicable predaceous present procedure proportion of fir pupae pure stands rapidly reason reduce reproduction result ring sample plots silken silvicultural small-unit plan species spruce and balsam spruce and fir spruce budworm STAND OF BALSAM standpoint tion units University of Minnesota upper crown canopy usually white spruce worm