Douglas-Fir Beetle Management

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 root disease severity, spread, and which will ultimately reduce stocking, subsequent tree mortality. percent of Douglas-fir, average stand age or size, will produce stand

Hazard Rating: Identifying susceptible stands

Stand susceptibility is based on individual tree susceptibility characteristics associated with past characteristics as well as those factors Landscape-scale outbreaks. Furniss, and others which seem to delimit susceptible hazard rating (1979), stated stand susceptibility is stands. Trees on which attacks are positively correlated with the more dense and successful are those A technique to query proportion of Douglas-fir in the which are older, larger, more stand data for hazard stand, its density, and its age. dominant, and more productive of classification has been Furniss, and others (1981), identified attractant resins. developed by Randall and Tensmeyer (1999). Weatherby and Thier (1993) Hazard Rating system Stands are hazard for the Intermountain West rated according to the system of Weatherby and Thier (1993). This Based largely on the observations of Furniss, and others system provides an (1981), but on other published and observed data as well, their easy way to hazard hazard-rating system enumerates the following “high hazard” rate stands over a conditions for Douglas-fir stands: landscape and can help prioritize areas for treatment. Stand density:  Stocking greater than 250 square feet basal area Percent Douglas-fir in stand:  Greater than 50 percent Average stand age:  Greater than 120 years Average diameter Douglas-fir sawtimber:  Greater than 14 inches Page 6 Back to menu Douglas-fir Beetle management Chapter 4.5

Risk Rating: Predicting levels of mortality in highly susceptible stands

Model to Predict mortality (Negron and others 1999)

Preventive A model to predict Douglas-fir beetle-caused mortality management in highly susceptible stands of Douglas-fir

is the most For western Montana/northern Idaho, for Douglas-fir stands of effective and otherwise high-hazard conditions this formula can be used to approximate economical anticipated beetle-caused tree mortality.

method of DF mortality = 13.2 + 0.33(DF basal area) reducing mortality The following damage class levels based on Douglas-fir basal area and attributable to average basal area killed by DFB were determined the beetle. Douglas-fir Basal Risk of Tree Average Douglas-fir Basal Area (ft2/acre) Mortality Area Killed by DFB (ft2/acre) <115 Low 37 115-230 Medium 69 >230 High 112 or more

Factors initiating outbreaks

Douglas-fir beetle outbreaks are of building high populations in such typically initiated by some type of material in a short period of time stand disturbance-the most common because of little or no host being windthrow, snow breakage or resistance. New generations emerge other weather-related phenomena. and attack susceptible green trees in Downed trees, logs, or other large- the surrounding stand. Once an diameter debris are very attractive to outbreak has started it normally lasts Douglas-fir beetles. Partially burned 2-4 years in an area. During trees after fires and trees defoliated droughty conditions, the beetle by western spruce budworm or outbreak may be prolonged for Douglas-fir tussock moth may also several years. trigger outbreaks. Beetles are capable 4.5 Back to menu Douglas-fir Beetle management Page 7

Prompt Removal of Windthrow Timely salvage of down, damaged or infested material, hauled from the severely weakened Douglas-fir is a woods, must be processed prior to primary means of preventing beetle beetle flight to prevent new outbreaks. Such activity must be outbreaks from being initiated near accomplished either before beetles mill sites. attack it initially, or before they emerge the following spring. Beetle- Trap Trees Because Douglas-fir beetles prefer groups of 3 to 5 trees. Diameters freshly downed trees to standing should be 15 inches or larger. Trees ones, a trap-tree program can be should be dropped in the shade and useful in suppressing beetle left unlimbed and unbucked. Trees Trap trees populations. Beetles are so effectively left in the sun, or where a major must be attracted to felled trees that green portion of the bole receives direct trees in the area are rarely attacked sunlight, do not attract beetles nearly removed as except for a few standing trees as well as those in a shaded soon as immediately adjacent to the downed environment. Trap trees should be practical trees. Trap trees are used to lure left on site until about mid-July to beetles into felled trees that will be attract beetles throughout their flight following subsequently removed. period. They should be removed as beetle flight to soon as practical following beetle be effective. Trap trees should be cut prior to flight but certainly before the next beetle flight in early spring (by April generation of beetles fly the 1). Trap trees could be dropped in following April 1. If infested logs are late fall, if done sufficiently late that not subsequently removed, tree they don’t dry significantly before mortality will likely increase. spring. Felled trees should be cut in

Timing of Harvest An adjunct to a trap tree program is A common and practical application the judicious timing of harvests to of this technique is to cut the right-of take advantage of the beetles' natural -way trees immediately prior to, or attraction to downed trees. Trees during beetle flight and allow the cut dropped in early spring, prior to trees to serve as trap trees. The cut about April 1, and left through beetle trees need to be removed prior to fall flight, can attract and hold beetles to snows to assure the brood is the site being harvested. This removed from the forest. technique can effectively prevent any beetles in the area from dispersing to other sites. Again, infested trees must be removed before subsequent beetle emergence. Page 8 Back to menu Douglas-fir Beetle management Chapter 4.5

Pheromones Attractant pheromones to manipulate beetle populations

When contemplating harvest in next generation of beetle flight or Douglas-fir forests with low beetle additional tree mortality is likely to populations, attractant pheromone occur. Tree baits effectively attract tree baits can be used to keep beetles beetles not only to the baited tree, in a specific stand that is scheduled but there is almost always “spill for removal. Tree baits can be used over” to adjacent, unbaited trees. in planned clearcuts, along rights-of- Harvest plans should include Attractant pheromone tree way, or in any other situation where removal of all attacked trees. In bait beetle populations exist and baited partial cutting, tree baits should be trees are certain to be removed used with caution to make sure that following their attack. Attacked beetles do not attack any selected trees must be removed prior to the leave trees. MCH provides short-term Anti-aggregation pheromones to protect trees and stands protection of high-value MCH (3-methylcyclohex-2-en-1-one) windthrown trees and therefore trees but must is a natural anti-aggregation prevent population buildup and be applied pheromone produced by Douglas-fir subsequent tree mortality. before beetles beetles to prevent overcrowding and fly in the optimize brood survival in individual MCH has been synthetically spring. trees or logs. It gives a “no vacancy” produced and formulated in two signal to other beetles in the area, different, currently registered, causing them to avoid an already releasing devises: fully colonized tree. Commercially  plastic bubble capsules that are available MCH is a tool that can be stapled to individual trees used to protect trees and stands  tiny polymer flakes that are from Douglas-fir beetle-caused aerially applied mortality that would adversely impact resource management MCH has successfully provided short objectives. MCH can also be used to -term protection of trees in reduce beetle colonization of campgrounds, administrative sites, and high value stands. However, this temporary approach should only be applied until stand conditions are changed to be less susceptible to Douglas-fir beetles or until beetle populations subside. To be most Above: MCH bubble effective, MCH should be applied capsule before beetles fly in the spring. For more specific information in using Right: MCH polymer MCH bubble caps, see Ross et al. flakes 2006. 4.5 Back to menu Douglas-fir Beetle management Page 9

Natural Control

According to Furniss and Orr (1978), Predatory beetles that help to keep bark beetle populations in check. resistance of live trees is the most important natural factor controlling Douglas-fir beetle populations. As an outbreak progresses and beetles are forced into increasingly less susceptible trees, the proportion of unsuccessful beetle attacks increase and populations decline.

Climate and weather also influence beetle populations. A sudden, severe The checkered beetle (Clerid) is Ostomid adult beetle. cold snap in late fall before beetles predatory on adult bark beetles. They are predatory on adult bark beetles; are prepared for winter can cause attacking them on the significant beetle mortality. outside of the tree. Prolonged cold, rainy spring weather important insect parasite is a may disrupt the beetles’ flight period. Braconid wasp which parasitizes the At the other extreme, droughty beetle's larval stage. Predators conditions stress host trees and favor include Dolichopodid flies, the population buildups. larvae of which prey upon beetle larvae; and Clerid and Ostomid Naturally occurring parasites and beetles which are predaceous on predators play a role in population both the larval and adult stages. reduction during non-outbreak This is the larval form of conditions, but apparently are not Woodpeckers feed on wood borers a predatory beetle. It important regulating factors when in Douglas-fir trees but have preys on bark beetle lar- beetle populations are extremely high minimal effect on Douglas-fir beetle vae under the bark of at- during outbreaks. The most populations. tacked trees.