Revised 2011 Forest Health Protection and State Forestry Organizations Chapter 4.5 WEB May 2011 Douglas-fir Beetle Management Sandra Kegley Topics Dendroctonus pseudotsugae Hopkins Management overview 1 Identification 2 Douglas-fir beetle is the most destructive bark beetle of Life History 3 Douglas-fir in the northern and central Rocky Life Cycle Illustrated 3 Mountains. Characteristics of 4 susceptible stands Reducing Stand 5 Susceptibility Outbreaks are brief but damaging Hazard Rating 5 Epidemics, though usually short- feet. As more of the susceptible hosts Risk rating 6 lived, may devastate susceptible are killed, and attacking beetles are stands before subsiding. Outbreaks forced into increasingly-less Factors initiating 6 outbreaks are usually triggered by a disturbance susceptible trees, populations decline. such as wind-throw, fire scorch, or Thereafter, mortality is confined to Removal of windthrow 7 defoliation. Populations expand individual trees or small groups. Low rapidly in such weakened material beetle populations are maintained in Trap Trees 7 and subsequent generations of root diseased or other weakened trees. Harvest; timing 7 beetles attack and kill surrounding Pheromones 8 green trees. During outbreaks, Outbreaks typically last 2 to 4 years groups of dead trees may total 100 or but may be prolonged during periods Natural control 9 more and yearly mortality may of drought. Other Reading 9 extend into the millions of board Field Guide Management Guide Management options for Douglas-fir beetle include : Key Points Prevent outbreaks 1. Prevention. Prompt salvage of windthrown, fire damaged, or by removing windthrow and defoliated Douglas-fir; judicious timing of logging and prompt other damaged removal or disposal of logs, large slash and cull material to trees. eliminate potential brood sites. Trap trees are 2. Hazard Rating and Stand Manipulation. Identification and effective in reducing silvicultural treatment of high-hazard stands to reduce local populations. susceptibility. Use hazard rating 3. Trap Trees and Pheromone Tree Baits with Tree Removal. Felled to identify trap trees and attractant pheromone baited trees are used to lure susceptible stands. beetles into logs and trees that will be removed and processed. 4. Anti-aggregation Pheromones. Used to protect high-value trees Pheromones can provide short-term and stands or prevent beetle colonization of windthrown trees. protection of high- value trees. Page 2 Back to menu Douglas-fir Beetle management Chapter 4.5 Recognizing Douglas-fir beetle attacks Evidence that a tree has been female beetles as they bore upward successfully attacked is orange- through the phloem. Galleries are brown boring dust found in bark parallel to wood grain and are crevices on the lower portion of the commonly 8 to 10 inches in length, tree's bole or on the ground at its usually longer in downed logs. Eggs base. Wind and rain may remove the are laid in groups, alternately along dust, however, and since beetle opposite sides of galleries. After attacks are often high on the bole, hatching, larvae mine outward from, careful inspection may be required to and perpendicular to, the egg gallery determine if beetles are present. An as they feed in the phloem. occasionally evident sign of infestation may be clear resin streams Several months after a tree has been which have exuded from the upper attacked, its foliage begins to level of attacks-typically 30 to 35 feet discolor. Needles first turn yellow, off the ground. These pitch then orange, and finally a reddish Orange-brown boring streamers are often visible for a brown. Discoloration rate varies with dust is evidence of considerable distance. Streams of local conditions and individual trees. successful attack by pitch lower on the bole may be During dry years, trees fade more Douglas-fir beetle. evidence of unsuccessful attacks or quickly-occasionally becoming other injury. As a rule, successful yellowish-green to orange later the attacks can only be confirmed by same year they are attacked. removing sections of bark to reveal Typically, trees begin to fade the year egg galleries, eggs, and/or developing following attack. Tree-to-tree fading brood. also varies with resistance to the pathogenic fungi introduced by the Distinctive egg galleries are beetles. constructed beneath the bark by Recognizing Douglas-fir beetle When the larvae have completed heads; pupae white to cream- their development, they construct colored. Immature beetles are light pupal cells at the ends of their brown, becoming dark brown to feeding galleries. Pupal cells may be black, with reddish wing covers, as well within the bark. Larvae are they mature. Some beetles may be white, legless grubs with brown totally black. Egg galleries of Douglas- fir beetle are vertical and the larval galleries are in alternating groups. 4.5 Back to menu Douglas-fir Beetle management Page 3 Life History Douglas-fir beetle has one re-emerge to make a second attack in generation each year. Over wintering mid- to late-summer. This second Western larch takes place beneath the bark of the flight (in some years nearly a may occasionally tree in which they developed and continual flight) usually accounts for occurs mainly as adults. A small less than ten percent of the yearly be attacked, but percentage may over winter as larvae. total of attacked trees. Often, these successful brood Spring emergence of adult beetles later attacks fill in trees which were development has varies with location and weather, but attacked during the initial spring only been usually occurs from mid-April to flight. recorded in early June. Beetles that have passed Broods require one year to downed trees. the winter as larvae complete their complete their development. Beetles development in spring and early emerging in spring are from the summer. Those emerge and attack previous spring's brood and beetles host trees in mid-summer. flying later in the summer are In addition, a few adults that typically from summer broods. made initial attacks in the spring may Trees killed by Douglas- fir beetle will have red crowns several months after a successful attack. Douglas-fir beetle has one generation each year. Page 4 Back to menu Douglas-fir Beetle management Chapter 4.5 Characteristics of Susceptible Douglas-fir Stands Density been observed on most of the Density-related factors reflect the subalpine fir types in which Douglas- importance of moisture stress and fir is seral. The most susceptible shaded-stem environment. The stands have a high percentage of Old, dense stands denser the stand, the higher the Douglas-fir. of large diameter susceptibility to beetle attack. Data Douglas-fir are suggest stands over 80 percent of Stand Age and Tree Diameter. highly normal stocking are most vulnerable. Average age of most Douglas-fir susceptible. killed exceeds 120 years. In Habitat Type and Species outbreaks and in densely-stocked Diversity. stands, younger trees may be killed. No definitive correlation between Larger diameter dominant and co- habitat type and beetle- caused dominant trees are more susceptible mortality has been developed. than intermediate and suppressed However, mortality is usually greatest trees. on the more moist habitat types where Douglas-fir grows most Disease. productively. Warm, dry sites may There is a relationship between root- produce susceptible stands unless diseased Douglas-fir and endemic they are so harsh that tree growth is populations of beetles. That sparse and slow. Little mortality has relationship is not as pronounced Douglas-fir beetle often kills groups of adjacent during outbreaks. The presence of trees in successive years. root disease in mature trees likely Older dead with a little contributes to their susceptibility to remaining foliage are beetle attack by exacerbating the commonly found near effects of moisture stress. recent mortality. Groups such as this are a good Injury. place to look for fresh Injuries such as wind and snow attacks which will have breakage, fire scorch, or defoliation boring dust on stems but predispose trees to beetle attack. green crowns. However, groups of beetle killed trees can also occur miles from previous year Resistance to beetle population expansion increases as: mortality. 1. susceptible trees are killed by beetles, 2. stand density is reduced through harvesting, 3. or environmental stress is reduced through improved moisture/ weather conditions. As infested-group size declines, and a higher proportion of attacked trees survive, natural enemies of the beetle play a bigger role in population reduction. Populations are then maintained at endemic levels through host resistance and natural enemies until conditions conducive to population buildup occur once again. 4.5 Back to menu Douglas-fir Beetle management Page 5 Reducing Stand Susceptibility Reducing stand susceptibility is best conditions less favorable to Douglas- A necessary first step in accomplished by changing one or fir beetles. the prevention of beetle more of the “high hazard” outbreaks is the conditions through some type of In many Douglas-fir forests, the identification of stands stand manipulation. Alternatives presence of root disease should be most likely to support include commercial thinning, or any considered and evaluated before an epidemic-hence, the of the several regenerative methods, thinning. Any type of partial cutting value of a hazard- which will help meet stand and site in root-diseased stands can increase rating system. resource objectives. Any method