Pests of Specific Crops

Pest Description
PSEUDOTSUGA - DOUGLAS FIR
Diseases:
Diaporthe Canker (Diaporthe lokoyae; anamorph
Phomopsis lokoyae): This fungus infects new
shoots. The sunken cankers are elliptical and
differ in size. Larger cankers can be up to 75 cm
long. They develop during the dormant season.
Dieback occurs when a limb is girdled. Tiny,
black fruiting bodies (pycnidia) are found in
the cankered area.
Douglas Fir - Cottonwood Rust (Melampsora
occidentalis): Yellow rust pustules are present
on underside of needles, which turn yellow
and die prematurely. Cottonwood leaves
develop angular, yellow spots on the upper leaf
surface that correspond to yellow and brown
rust pustules on the lower surface.
Grey Mould/Seedling Blight (Botrytis cinerea):
Individual new shoots wilt and turn brown
early in the growing season, causing
conspicuous blight in unusually wet springs.
Needle Cast (Rhabdocline pseudotsugae): Yellow spots
appear on current season needles in early fall.
Spots enlarge the following spring and turn
into purplish-brown bands in May or June.
Spores shed from these bands infect newlyopening
needles in spring. The old needles fall
off leaving a single year’s needles on the tree.
Cool, wet weather promotes infection.
Needle Cast (Rhizosphaera kalkhoffi): Small yellow to
greyish-green, mottled spots appear on current
year’s needles in late summer, particularly on
lower branches. Spots then turn purplishbrown.
See PICEA: Needle Cast for a full
description of this disease.
Chemical Control
(rate per 100 L water; or per
unit area if indicated)
Fungicides applied to control
other diseases listed below will
also help to prevent infection
by this fungus.
Cultural Management
Keep trees healthy. Prune out
infected limbs well below the
canker. Remove prunings
from the area and burn, bury
or chip, since spores from
dead, cankered limbs can
cause new infections.
Both hosts are required for
survival of the rust.
Susceptible cottonwoods
include Populus trichocarpa,
P. balsamifera and hybrid
poplars. These should be
removed from the
perimeter of fields
producing Douglas fir. See
also POPULUS: Rust.
See General Disease Management: Botrytis Blight and Storage
Moulds, Chapter 9.
BRAVO Ultrex 90 SDG: 1.3-2.7 kg/ha
COPPER SPRAY 50: 400 g
DACONIL 2787F: 2.4–4.8 L/ha
DACONIL Ultrex: 1.45-2.9 kg/ha
DITHANE DG, M-45 or WSP 80WP: 275-350 g
PENNCOZEB 80WP: 275-350 g
Treat when new growth is 1-5 cm in length. Repeat sprays
every 10-14 days in cool, wet springs.
BANNER MAXX: 35 mL (for use
on Christmas trees only)
Fungicides applied for
Rhabdocline Needle Cast (see
above) will help to control this
disease also.
Seedling Blight (Sirococcus conigenus): See under PICEA and in General Disease Management: Sirococcus Blight, Chapter
9.
Swiss Needle Cast (Phaeocryptopus gaeumannii):
Fungal fruiting bodies appear as rows of black,
pinhead-like dots on the underside of needles.
There may be defoliation of one- and two-yearold
needles in early spring.
Insects:
Cooley Spruce Gall Adelgid (Adelges cooleyi): Insects
attack both spruce and Douglas fir. On Douglas
fir they are present as woolly aphids in spring.
See under PICEA-SPRUCE.
Fungicides applied for
Rhabdocline Needle Cast (see
above) will help to control this
disease also.
See General Insect and Mite Management: Aphids and Adelgids,
Chapter 9.
Nursery Production Guide Pests of Specific Crops • 33