CAMELLIA CANKER, DIEBACK.
At least two fungi (Glomerella cingulata
and Phomopsis sp.) in addition to unfavorable environmental conditions cause trouble on camellia. Tips die back, leaves turn dull green
and then brown, the stems are brown and eventually girdled. The fungi
apparently gain entrance through bud scars in spring, young buds in
summer, and pruning wounds.
Control. Prune out dead and dying twigs and limbs. Paint large cuts
with bordeaux paint or other disinfectant wound dressing. Copper sprays
are considered helpful.
CROWN CANKER OF DOGWOOD, BLEEDING CANKER OF ELM, MAPLE, OAK,
BEECH (Phytophthora cactorum).
Foliage is light, thin, with a
bronze cast, twigs die back, and from cankers on the trunk there oozes
a reddish-brown liquid which hardens to resemble dried blood. The
fungus remains inside the cankered area, but toxins produced by it cause
the general weakening of the tree and sometimes death. On dogwood the
canker develops on the lower trunk near the ground. The area is sunken
with bark drying and falling away, and the inner bark and wood are discolored. The fungus lives in the soil and enters through wounds, often
those made in transplanting or by a lawn mower. The tree dies when
the canker entirely surrounds the trunk.
Control. Remove discolored wood and healthy wood for 11/2 inches
around edge of canker. Paint with orange shellac. Avoid wounds; a guard
around the base of a dogwood will keep it from being barked by a lawn
mower. Do not plant a new dogwood in a location where one has died
of crown canker. Chemotherapy, injection of an antitoxin into the vascular system of a tree, often prevents death from bleeding canker, by neu-
tralizing the poison produced by the fungus. Helione Orange is one
chemical which has been successfully used by tree experts.
BOXWOOD CANKER. See Volutella Blight under BOXWOOD.
CYTOSPORA CANKER of POPLAR and WILLOW (Valsa sordida-Cytospora
chrysosperma) and SPRUCE (C kunzei).
On poplar and willow,
cankers appear on trunks and larger branches, more frequently on trees
weakened by drought or pollarding (topping). Western cottonwoods are
quite susceptible, but the variety Rio Grande is resistant. The diseased
bark dies in more or less circular areas, and the surface is dotted with
black fruiting bodies from which yellow or reddish-brown tendrils of
spores ooze out in wet weather. Spruce canker and twig blight is common
on ornamental Norway and blue spruce in the Northeast. Browning and
death of branches starts near the ground and progresses slowly upward.
Infected branches have a large flow of resin; needles often drop. Spores
are splashed from branch to branch by rain, and entrance is through