Integrated Pest Management for Christmas Tree Production: A ...

Figure 3. Eggs found tucked
in the needle bud before buds
are fully broken. Courtesy of
Rayanne D. Lehman, PDA
Figure 4. Young larva found
inside a needle. Courtesy of
Rayanne D. Lehman, PDA
Figure 5. Early evidence of galls;
needles are beginning to kink
(late July). Courtesy of Tracey
Olson, PDA
Figure 6. Advanced gall
symptoms (November).
Courtesy of Tracey Olson, PDA
Figure 7. Mature larva still in
the needle (December).
Courtesy of Tracey Olson, PDA
Eggs (Fig. 3) hatch within a few days and
larvae (Fig. 4) bore directly into the young
needles to feed throughout the summer. As
the larvae feed and grow, galls form in the
needles and cause them to kink (Fig. 5).
By late summer, the galls will begin to
turn yellow and then brown (Fig. 6). In late
fall, the full-grown larvae (Fig. 7) exit the
needles and drop to the ground to overwinter,
leaving a distinct triangular exit hole
in the underside of the needle (Fig. 8).
A single generation occurs each year.
Monitoring and Management
Strategies
Plantation Establishment
• Plant late breaking tree varieties to
decrease midge damage.
• Remove overgrown Douglas-fi rs from the
perimeter of the block. Damage is often
more severe on older trees.
Preseason
• Place emergence traps under the north
side of previously infested trees by April
1 or before the daily temperature reaches
60°F for several days (Fig. 9). See Appendix
E: Insect Trap Use and Construction
for information on trap construction.
• Place at least three traps per fi eld and
check every day until the fi rst midge appears.
Record the number of midges in the
trap jar before emptying and replacing the
jar. Continue monitoring until no midges
are present for several days.
Growing Season
• Growing degree days: The adult midges
emerge from the soil beneath trees at
200–400 GDDs (based on midge population
monitoring in Pennsylvania).
• Threshold level: No established threshold
level exists for this pest.
• Scout in August for infestation. Mark
trees that exhibit symptoms to aid with
trap placement and distribution of control
chemical next spring.
• At the end of the season, evaluate results
and update records.
Figure 8. Needle
showing larva
exit hole.
Courtesy of
Tracey Olson,
PDA
Control Options
Biological
• Encourage and protect natural predators
such as tiny parasitic chalcid wasps.
Ill-timed chemical application is not
effective and may kill natural enemies.
Mechanical
• Remove heavily infested trees in early fall
before larvae exit the needles.
Biorational
• No recommendations are available
at this time.
Chemical
• Base application on collection of adults
in emergence trap. Chemicals will not be
effective against eggs, only adults. First
application should be made within a day
of collection of the fi rst midge.
• Consider a second application in 2 weeks
if adults are continuing to emerge.
Next Crop/Prevention
• Purchase and plant pest-free nursery stock
from a reputable company.
Figure 9. Emergence trap placed under a
previously infected tree. Courtesy of Sandy
Gardosik, PDA
NEEDLE DISCOLORATION AND INJURY ................................................................................................................................................................................................................................................ 38