Biology Reference
In-Depth Information
disease and causes chronic cases to become
acute.
Crown Canker
, collar rot, is the most serious
disease of dogwood reported in New York, New
Jersey, and Massachusetts. The first symptom is
a general unhealthy appearance, with leaves
smaller and lighter green than normal, turning
prematurely red in late summer. Leaves may
shrivel and curl during dry spells (normal leaves
often do likewise). Twigs and large branches die,
frequently on one side of the tree. The canker
develops slowly on the lower trunk near the soil
level. Inner bark, cambium and sapwood are
discolored; the cankered area is sunken; the
bark dries and falls away, leaving wood exposed.
Trees die when the canker extends completely
around the trunk base or root collar. The fungus
lives in the soil in partially decayed organic mat-
ter, and spores are washed to nearby trees.
Entrance is through wounds. The disease affects
transplanted dogwoods, seldom natives growing
in woods.
Control
Transplant carefully, avoiding all unnec-
essary wounds; avoid hitting base with lawnmower,
byusingawireguardaroundthetree.Itisdifficult
to save trees already infected, but cutting out small
cankers and painting the wound with bordeaux
paste is worth trying. If trees have died from
crown canker, do not replant with dogwoods in
the same location for several years.
Rhododendron Dieback
, is a disease in which
terminal buds and leaves turn brown, roll up, and
droop as in winter cold. A canker encircles the
twigs, which shrivel with the terminal portion
wilting and dying. In shady locations leaves
have water-soaked areas, changing to brown,
zonate spots. Do not plant rhododendrons near
lilacs, for they are blighted by the same fungus.
Prune diseased tips well below the shriveled part,
and spray after blooming with bordeaux mixture,
two applications 14 days apart.
Trunk Canker of Apple
, is an irregular canker
often involving the entire trunk and base of scaf-
fold branches, the first outward symptom a wet
area on bark. Trees must be 5-years old or older
for infection. Grimes Golden and Tomkins King
are
Phytophthora cinnamomi
Basal Canker
of
Maple, particularly Norway maple. Trees have
a thin crown, fewer and smaller leaves, and die
a year or two after cankers are formed at the base
of the trunk. Sapwood is reddish brown; the roots
decay. Remove diseased trees. Plant new Norway
maples in good soil, well drained, rich in organic
matter; treat injuries at base of trunk promptly.
See under
Wilt Diseases
for other
manifestations of this pathogen.
Phytophthora syringae
Pruning Wound Can-
ker
of almond.
▶
Rots
and
▶
Plenodomus
Deuteromycetes, Coelomycetes
Pycnidia dark, immersed, irregular in shape and
opening irregularly; conidia hyaline, one-celled,
oblong; parasitic.
Aposphaeria fuscomaculans (formerly
Plenodomus fuscomaculans
).
Canker
on apple.
Plenodomus fuscomaculans
(see
Aposphaeria
▶
fuscomaculans
).
Canker
on apple.
Pseudonectria
Ascomycetes, Hypocreales
Perithecia superficial, blight-colored, smooth;
spores one-celled, hyaline.
Pseudonectria rouselliana
Nectria Canker
of
boxwood,
Leaf Cast
,
Twig Blight
. The perithecia
are formed on dead leaves, but the fungus is
thought to be the teleomorph state of
Volutella
buxi
, which see.
Pseudovalsa
Ascomycetes, Diaporthales
Perithecia in a stroma; spores ark, with several
cells.
Pseudovalsa longipes
Twig Canker
on coast
live oak and white oak.
especially
susceptible,
often
being
completely girdled.
