Pests of Specific Crops

Pest Description
Berckmann’s Blight / Seiridium Blight / Coryneum
Canker (Seiridium spp., teleomorph Coryneum
berckmannii): Severe twig and branch canker
occurs only on Platycladus orientalis (formerly
Thuja orientalis). Foliar blight can also occur on
Thuja plicata and Chamaecyparis spp. Foliage
looks greyish and infected twigs dieback.
Young twig tips are infected, and the disease
progresses inward on the tree. Spores infect
twigs in late September but disease symptoms
may not be apparent until the following spring.
Tiny, black, fungal fruiting bodies are found in
late summer/fall where twigs and branches are
girdled.
Cedar Flagging (physiological): Common on Thuja
plicata (western red cedar). In late summer,
patches of foliage turn yellow to reddish-brown
on branches scattered about the tree.
Foliar Blight/Dieback (Kabatina thujae): This disease
affects Thuja occidentalis and Chamaecyparis spp.,
causing leaf and shoot dieback in spring. It is a
sign that the plants are not growing well.
Keithia Blight (Didymascella thujina): Tiny, circular,
brown to black, fungal fruiting bodies appear
on scale leaves in late spring. The leaves then
turn brown and affected areas fall out. Later,
infected leaves drop, leaving branches with a
sparse or bare appearance. Dormant spores
adhering to the foliage in the fall can germinate
and cause new infections during propagation.
Leaf Browning/Purpling (Environmental): Foliage
takes on an overall brownish or purplish colour
in early spring. This colour change may occur
rapidly. Healthy plants will green-up as the
growing season progresses.
Note: During flowering, some varieties may
exhibit an overall reddish-purple colour. The
colour may become suddenly more noticeable
in years with more intense flowering.
Insects and Mites:
Cypress Tip Moth (Leafminer) (Argyresthia
cupressella): Adult moths are silvery-tan in
colour and are active in early June. Eggs are
inserted into the green tips of one and twoyear-old
twigs. The larvae tunnel into leaf
scales and remain there until the next spring.
Infested twigs turn yellow, then brown in late
winter. A cocoon is spun around the foliage in
early June of the second year for the pupal
stage. Two to three weeks later, adults emerge.
Mites: Damage usually occurs first at the bottom of
the plant and on the south side. Monitor by
gently shaking the foliage above a sheet of
white paper.
Chemical Control
(rate per 100 L water; or per
unit area if indicated)
COPPER SPRAY 50: 400 g
DITHANE DG, M-45 or WSP
80WP: 275-350 g
PENNCOZEB 80WP: 275-350 g
Spray twice every fall and
again in spring to protect new
foliage.
COPPER SPRAY 50: 400 g
Apply once in the fall and
every 2-3 weeks in the spring
to protect new growth.
Treat at least 3 times between
March and mid-June.
See General Disease
Management: Keithia Blight,
Chapter 9.
MALATHION 500E: 250 mL
In late April, mid-June and
early July, spray to control
larvae outside the foliage or
moths before egg laying.
Cultural Management
Prune out affected branches
and twigs. This disease is the
main limiting factor to the
successful growing of P.
orientalis in Coastal BC.
Dying twigs are often
infected by secondary fungi
so a laboratory diagnosis is
often needed to confirm this
disease.
A natural occurrence; not
damaging to the tree. May be
more severe in droughty
years.
Examine soil for correct pH,
nutrient levels and drainage.
Avoid overhead watering.
Irrigate early in the day.
Avoid overhead watering of
Thuja plicata. T. plicata
‘Atrovirens’ and ‘Excelsa’ are
especially susceptible. Locate
nursery beds of these varieties
away from mature T. plicata
windbreaks. Do not propagate
from infected plants.
Cold temperatures in winter
and early spring, rather than
drought, are responsible for
the temporary leaf browning.
Provision for shelter or
windbreaks may help. T.
occidentalis ‘Smaragd’ is less
susceptible than other
varieties.
See General Insect and Mite Management: Mites, Chapter 11.
Nursery Production Guide Pests of Specific Crops • 41