Defoliators

Overview

bullet#1 pest in Canada, # 2 pest in BC
bulletFETCH21 has an extensive list of defoliators in BC: http://web.unbc.ca/ctl/webcourses/fsty307/defol/defol.html
bulletFPC Guidebook has a shorter list but provides extensive details on each


Source: http://www.for.gov.bc.ca/tasb/legsregs/fpc/fpcguide/defoliat/table1.htm

 
bulletconsidered "aggressive", in that tree vigour is of no consequence for attack
 
bulletdamage
bulletprimarily growth loss (and predisposition)
bulleta few can cause mortality (Douglas-fir tussock moth, gypsy moth, Hw looper,  black-headed budworm??)

 
bulletDefoliator Categories
bulletby tissue
bulletleaf chewers consume all portions of leaf, but some are efficient and others wasteful
bulletskeltonizers (elm leaf beetle)
bulletleaf miners (inside the leaf, Pl leaf miner)
bullet"suckers" - aphids can cause defoliation, spruce aphid
 
bullettissue age
bulletnew (budworms)
bulletold (spruce aphid)
bulletold & new - Douglas-fir tussock moth
 
bullethost specificity
bulletpolyphagous - many hosts, gypsy moth
bulletoligophagous - few hosts, spruce budworm (east, on fir & spruce)
bulletmonophagous - one host, larch case bearer

 
bulletOutbreaks
bulletsporadic (triggered by environment cues, e.g. temperature; western hemlock looper)
bulletperiodic (regular return intervals; Douglas-fir tussock moth every 9-10 years)
bullet4 stages of an outbreak
bulletendemic - usual level
bulletbuilding - population on the increase but hard to detect without careful monitoring (need 50% defoliation to notice it)
bulletepidemic (outbreak) - peak damage, easy to notice
bulletcollapse - due to 3P's, weather or lack of food

                                            Source: http://www.for.gov.bc.ca/tasb/legsregs/fpc/fpcguide/defoliat/fig9.htm

bulletDistribution vs. pattern
bulletdistribution = geographic range of the bug, often it is the outbreak areas that are mapped
bulletpattern = where on the landscape, often elevation bands due to temperature / moisture (spruce budworm on Fd, hemlock looper close to water)
 
bulletSeverity - intensity vs. extensive (extents)
bulletintensity - degree of damage in a stand (nil, low, moderate, high)
bulletextensive = geographic extents of current outbreak

 

L
M
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bulletDamage & Recovery
bulletdeciduous vs. conifer
bulletdominant vs. intermediate
bullettiming during the year - this Bud's for you!
bulletlongevity & severity (need to consider both ... remember the Spruce terminal weevil)

 
bulletImpacts
bullet↓ foliage, ↓ photosynthesis, ↓ growth, ↓ vigour
bulletcan lead to 'complexes' with root disease and or bark beetles
bullettop kill is common
bulletavenue for decay
bulletdeformity
bulletcone/seed loss
bulletmortality (if severe and long-lived)
 
bulletaesthetics & recreation
bulletthinner crowns
bullet↑ light to ground, ↑ vegetation, ↑ summer forage
bullet↓ thermal cover, ↓ snow interception
bullethuman health - allergic reactions
bulletwatershed processes - less ET, more water in system





 
bulletMonitoring / Detection
bulletIndirect - observation of people in the field (cruisers, forester, hikers, etc.), often only noted when late in build-up phase
 
bulletAnnual Overview Surveys
bulletAerial survey
bulletdone in late summer
bulletcreate sketch maps @ 1:100,000
bulletlow intensity, but great extents
bulletmay trigger follow-up survey (more intense air, or ground)


Source: http://www.for.gov.bc.ca/tasb/legsregs/fpc/fpcguide/defoliat/table5.htm
 
bulletGround Survey - Walk through
bulletdone on areas noted in aerial survey
bulletdone especially during building and collapse phases
bullettarget high hazard
bulletconfirm pest ID and intensity

 
bulletIntensive Surveys
bulletPredictive - to forecast the population/ damage next season; usually a follow-up survey done next spring
bulletadults - in summer with pheromone traps (done annually in some areas for Douglas-fir Tussock Moth)
bulleteggs - in late summer / fall; get an egg/foliage area ratio; good for all species
bulletL2 - w. spruce budworm, $$ so not often done, unless eggs not sampled and considering a treatment
 
bulletPopulation - to provide an estimate of the current population (i.e. this year, not predicting next year)
bulletconfirmation of a predictive sample - e.g. bud mining survey early in spring for budworms
bulletassess efficacy of control measures - done after treatment

 
bulletManagement Strategies
bulletLong Term - preventative, keep forest vigorous
  1. monitoring - annual aerial and walk through surveys
     
  2. species variety within stand and over the landscape
     
  3. varied age class distribution over the landscape
     
  4. open stand structure (esp. for Fd stands), sometimes clearcut is a better option
     
  5. stand vigour (aids with recovery) - mainly stand density (maybe fertilization?)
     
  6. biodiversity - WTP & snags ... primary excavators, secondary nesters ... birds!
     
  7. research

     
bulletShort Term - during outbreak
  1. monitoring - during outbreak - predictive and/or population
     
  2. spray insecticides ("chemical", Btk, NPV)
    bulletfoliage protection - protect this year's foliage
    bulletapply earlier in season to minimize defoliation, but won't get maximum kill
     
    bulletpopulation control - goal is "get the bug!"
    bulletapply later in season, more defoliation, but better kill rate
    bulletor use of NPV (sprayed early in season, but slow acting)


    Source: http://www.for.gov.bc.ca/tasb/legsregs/fpc/fpcguide/defoliat/table7.htm

     
  3. mating disruption - mess with the males so they can't find the females