Pests of Specific Crops

Pest Description
ULMUS - ELM
Diseases:
Dutch Elm Disease (Ceratocystis ulmi ): BC is free of
Dutch Elm Disease, which is spread by bark
beetles, such as the Native and European Elm
Bark Beetles. The vectors do occur in BC.
Beetles acquire the fungus in the fall when they
tunnel under the bark of infected branches to
breed. They spread the pathogen when they
emerge and feed on new, young twigs. The first
symptoms of disease are wilt and dieback of
branches in mid-summer, often on only one
side of the tree. Dark streaks can be found in
the sapwood of infected branches. American
elm is highly susceptible; Siberian and Chinese
elm may become infected but do not wilt and
die, so these resistant species rarely transmit
the fungus. Other fungal diseases may cause
branch dieback on elm with similar symptoms.
Wet Wood or Slime Flux (Erwinia nimmipressuralis,
and other bacteria): This bacterium is an invader
of old, weakened or damaged trees and is a
sign of other injury. It causes slimy, smelly
cankers on trunks and branches and/or
discolouration of interior wood. Exudate runs
down the trunk causing further discolouration
of the bark and attracts insects. It commonly
affects old poplars, horse chestnuts and maples.
Insects:
Elm Leaf Beetle (Xanthogaleruca luteola): Attacks all
elm species. The black, grub-like, larvae
skeletonize the lower side of the leaf. Can lead
to premature leaf drop. In the spring, the adult
beetles lay yellow eggs in clusters on the
underside of leaves. Larvae pupate on the
ground at the base of the tree or in bark
crevices. Adult beetles leave the tree to find a
suitable overwintering site in the fall.
European Elm Bark Beetle (Scolytus multistriatus): See
Dutch Elm Disease (above).
Woolly Apple Aphid (Eriosoma larigerum): This aphid
causes clusters of rolled, twisted, and dwarfed
leaves at the growing tip of elm shoots. Eggs
overwinter on elm. After hatching in the
spring, the insect then moves to apple, where it
feeds on leaves and roots. It is present all
summer.
Chemical Control
(rate per 100 L water; or per
unit area if indicated)
Tree Injection:
Cultural Management
ARBOTECT 20-S: See product label for application rate, etc.
To control the disease-vectoring beetle, see European Elm Bark
Beetle (below).
Management: BC and Alberta remain free of Dutch Elm
Disease. Rapid identification and removal of infected trees
before beetles can breed in dead branches is essential to
prevent its spread. Contact the Pacific Forestry Centre,
Victoria, the Canadian Food Inspection Agency, or your local
BCMA office immediately, if you observe wilt disease
symptoms on an Ulmus tree. Do not bring Ulmus or Zelkova
into BC. See British Columbia Plant Protection Regulations,
Chapter 2 for information on the voluntary nursery
certification program for the disease. Nurseries, parks and
landscapers are advised to monitor American elm for dieback
and prune out any dead or dying elm branches in the
dormant season to prevent beetle breeding.
Affected trees may die
quickly, or limb by limb, and
are a risk to fall down. Trees
may be cleaned up to some
extent by drilling holes just
below the affected area and
inserting plastic pipe to drain
exudate from the trunk. An
infected tree will eventually
have to be cut down.
ACECAP 97: for rate, see label or Aphids and Adelgids,
Chapter 11.
CONSERVE or SUCCESS 480 SC: 2.5 mL
ENTRUST 80 W: 1.5 g
ORTHENE 75% SP: Mist blower = 1,312 g/1,000 L; Hydraulic
sprayer = 637 g/1,000 L (do not apply to American elms)
THIONEX EC: 125-175 mL
THIONEX 50 W: 100 g
SEVIN T&O: 230-350 mL
Nursery: Apply insecticides to prevent beetle feeding. Follow
a regular spraying and monitoring program.
ACECAP 97: for rate, see label or Aphids and Adelgids,
Chapter 11.
INSECTICIDAL SOAP 47% or 50.5%: 2 L
POUNCE 384 EC: 9 mL
Greenhouse only:
IMPOWER 60WP: See label.
See General Insect and Mite Management: Aphids and Adelgids,
Chapter 11.
Nursery Production Guide Pests of Specific Crops • 43