Pests of Specific Crops

Pest Description
CORNUS - DOGWOOD
Diseases:
Anthracnose (Discula destructiva): Large wedgeshaped
blotches appear on leaves in spring.
Severe defoliation and twig cankers may result.
If repeated for several years, the trees may
weaken and eventually die. Cornus ‘Eddie’s
White Wonder’, C. florida (Eastern Dogwood)
and C. kousa (Japanese Dogwood) are more
resistant than C. nuttallii (Western Dogwood).
Crown Canker (Phytophthora cactorum): This soilborne
organism infects the base of the trunk
(crown) at the soil line, either through the roots
or through injury to the bark. Infected trees lack
vigour and slowly dieback. Wood beneath the
bark of cankers is discoloured. The tree dies
when the canker finally girdles the trunk.
Phyllosticta Leaf Spot (Phyllosticta): The symptoms
include circular to angular leaf spots with
purple borders that develop in late summer
and fall.
Chemical Control
(rate per 100 L water; or per
unit area if indicated)
Nursery crops:
BANNER MAXX: 28 g
Apply every 14 days; no more
than 4 applications per year.
NOVA 40W: 34 g
NOVA and BANNER have the
same mode of action. To prevent
disease resistance, do not
alternate these products.
Landscape:
Dormant sprays with lime
sulphur, or application of
fungicides as recommended for
Septoria Leaf Spot (see below)
may be helpful.
There are no effective chemical controls.
Cultural Management
Do not grow or sell highly
susceptible varieties. On small
plants isolated from large
infected trees, picking off the
first diseased leaves in spring
may be beneficial. Raking and
burning fallen leaves may
significantly reduce
overwintering inoculum. If
severe disease continues,
remove and replace with
more resistant varieties.
Management: Once this disease appears in a nursery, a
conscientious clean-up and sanitation program is required. Avoid
injury to the bark of established trees. Most infections of mature
trees occur through wounds. Surgery of small cankers can
prolong tree life. Clean out cankers during dry weather, paint
with shellac, then with tree emulsion. Leave wounds exposed to
air during summer. Do not cover with soil.
Water early in morning to
minimize the period of leaf
wetness.
Collect and dispose of leaves
in the fall.
Powdery Mildew (Microsphaera spp.): See General Disease Management: Powdery Mildew, Chapter 9. Information on the
susceptibility of Cornus species to powdery mildew is included in Appendix C.
Septoria Leaf Spot (Septoria spp.): Angular, greyish
spots with dark purple margins appear on
leaves. Black fungal fruiting bodies (pycnidia)
may be seen in these spots in humid weather.
Insects:
Dogwood Sawfly (Macremphytus tarsatus): The larvae
skeletonize the leaves of Cornus species, in
particular C. racemosa and C. sericea. Look for
the larvae on the underside of leaves. First
instars are almost translucent yellow, while
second instars appear to be covered with a
chalky powder. The last instar is 2.5 cm long
and is creamy-yellow with a black head and
black spots. The larvae overwinter in decaying
wood on the ground. Adult sawflies emerge
the following spring.
DACONIL 2787F: 250 mL
DACONIL Ultrex: 150 g
Apply at early bloom. Repeat
every 7-14 days as needed.
NOVA 40W: 34 g
See General Insect and Mite
Management: Sawflies, Chapter 11.
Rake up and burn, bury or
compost fallen leaves.
Nursery Production Guide Pests of Specific Crops • 11