APPENDIX D 



FOREST INSECT AND DISEASE REPORT 



INTRODUCTION 



This report discusses the primary causes of 

 damage and mortality that are currently, or have 

 recently been, affecting mature western larch 

 {Larix occidentalis), Douglas-fir {Pseudotsuga 

 menziesii), western white pine {Pinus monticola), 

 and grand fir (Abies grandis) within the proposed 

 Cilly Bug Salvage Timber Sale Project on Swan 

 River State Forest, Montana Department of 

 Natural Resources and Conservation (DNRC). 

 Details of the proposed salvage sale are 

 presented in the Cilly Bug Salvage Timber Sale 

 Proposal, available from Roger Ziesak of Swan 

 River State Forest. 



A walk-through inspection of the Cilly Bug project 

 sale area, in addition to a recent report on wood- 

 borer damage to western larch in northwest 

 Montana (Gibson 2004), revealed that the major 

 pathogens and insects either causing, or 

 contributing to, the damage and mortality are, by 

 tree species: 



• Western larch 



- Western larch dwarf mistletoe (Pathogen = 

 Arceuthobium laricis) 



- Flatheaded fir borer (Melanophila 

 drummondi) 



• Douglas-fir 



- Douglas-fir beetle (Dendroctonus 

 pseudotsugae) 



- Brown cubical root and butt rot (Pathogen 

 = Phaeolus schweinitzii) 



• Western white pine 



- White pine blister rust (Pathogen = 

 Cronartium ribicoia) 



- Mountain pine beetle (Dendroctonus 

 ponderosae) 



• Grand fir 



- Fir engraver (Scolytus ventralis) 



Indian paint fungus (Pathogen = 

 Echinodontium tinctorium) 



In addition to the pathogens and insects listed 

 above, the prolonged drought prior to 2004 would 



have caused physiologic stress in these mixed- 

 conifer stands. Drought stress can either 

 exacerbate the damage being caused by the 

 pathogens and insects already affecting these 

 trees or predispose them to damage from insects 

 that take advantage of stressed trees. 



RELEVANT BIOLOGY OF AND 

 MANAGEMENT STRATEGIES FOR THE . 

 PRIMARY PATHOGENS AND INSECTS 



• Vi^eMern larch diratf mistletoe 



Western larch dwarf mistletoe, caused by 

 Arceuttiobium laricis, is considered the most 

 important disease of western larch in the 

 Inland West (Beatty at al. 1997). Dwarf 

 mistletoes are parasitic plants that obtain 

 moisture and nutrients from their hosts, 

 resulting in a reduction in tree vigor, growth, 

 and seed production. Dwarf mistletoe 

 infections greatly decrease the growth of 

 western larch; 10-year basal-area growth of 

 trees in western Montana classed as lightly, 

 moderately, and heavily infected was 

 decreased 30 percent, 42 percent, and 65 

 percent, respectively, compared to that of an 

 uninfected western larch (Pierce 1960). 



The life cycle of dwarf mistletoe is generally 4 

 to 6 years in length, depending on the 

 species. Dwarf mistletoes spread when 

 seeds from the female mistletoe plants are 

 forcibly dispersed, often for 10's of feet, in the 

 late summer and fall; seeds that land on 

 susceptible hosts germinate the following 

 spring and infect the host tissues. Infections 

 on western larch eventually cause branches 

 to form dense clumps of twigs and branches, 

 also known as "witches brooms". In western 

 larch, these brooms are brittle and prone to 

 break off under snow load, thus leading to 

 gradual, top-down decline of the tree as more 

 and more branches are lost. Dwarf mistletoe 

 infection increases moisture stress in its host, 

 all the more so when there is a drought in 

 progress. 



Similar to most of Swan River State Forest, 

 incidence and severity of western larch dwarf 

 I mistletoe appears to be highly variable in the 

 Cilly Bug Salvage Timber Sale project area. 



Cilly Bug Salvage Timber Sale Project 



Page D-1 



