Biology Reference
In-Depth Information
Diaporthe vexans
Phomopsis Blight
of Egg-
plant,
Fruit Rot
, general in field and market, espe-
cially in the South. Destruction is often complete,
with every above-ground part affected. Seedlings
rot at ground level. The first leaf spots are near the
ground, definite, circular, gray to brown areas
with light centers and numerous black pycnidia.
The leaves turn yellow and die. Stem cankers are
constrictions or light gray lesions. Fruit lesions
are pale brown, sunken, marked by many black
pycnidia arranged more or less concentrically.
Eventually the whole fruit is involved in a soft
rot or shriveling. Spores winter on seed and in
contaminated soil. There is no fungicidal control.
Use resistant varieties Florida Market and Florida
Beauty.
Control
Spray small trees and nursery stock sev-
eral times during summer and fall with bordeaux
mixture.
Didymascella tsugae
Fobrella tsugae
).
Hemlock Needle Blight
. Needles of Canada hem-
lock turn brown and drop in late summer. Spores
are matured in apothecia on fallen needles with
new infection in spring. The damage is not heavy.
Fobrella tsugae (see
(see
▶
Didymascella tsugae
).
Hemlock Needle Blight
. Needles of Canada hem-
lock turn brown and drop in late summer.
▶
Didymella
Ascomycetes, Sphaeriales,
Mycosphaerellaceae
Dichotomophora
Perithecia (or perithecia-like stromata) membra-
nous, not carbonaceous; innate; not beaked;
paraphyses present; spores two-celled, hyaline.
Didymella applanata
Raspberry Spur Blight
,
Purple Cane Spot
,
Gray Bark
, general on rasp-
berries, also on dewberry, blackberry. Named
because it partially or completely destroys spurs
or laterals on canes. The disease, known in North
America since 1891, may cause losses up to 75 %
of the crop of individual plants of red raspberries.
Dark reddish or purple spots on canes at point of
attachment of leaves enlarge to surround leaf and
bud and may darken lower portion of cane.
Affected areas turn brown, then gray.
If buds are not killed outright during the winter,
they are so weakened that the next season's spurs
are weak, chlorotic, seldom blossoming. Pycnidia
of the anamorph
Phoma
state and perithecia are
numerous on the gray bark; ascospores are
discharged during spring and early summer; on
germination they can penetrate unwounded tissue.
Control
Keep plants well-spaced, allowing plenty
of sunlight for quick drying of foliage and canes.
Remove infected canes and old fruiting canes after
harvest. A delayed dormant spray of lime sulfur or
Elgetol may be advisable, followed by two sprays
of ferbam or bordeaux mixture, applied when new
shoots are 6 to 10 inches high and 2 weeks later.
Didymella bryoniae Gummy stem blight and
fruit spot; of watermelon.
Cankers and Diebacks
.
Dichotomophora lutea
Stem Blight
, of com-
mon parsley.
▶
Didymascella (Keithia)
Ascomycetes, Phacidiales,
Stictidiaceae
Apothecia brown, erumpent on leaves of coni-
fers; spores dark, two-celled, ovoid; paraphyses
filiform; asci two-to four-spored.
Didymascella thujina
Arborvitae Leaf Blight
,
Seedling Blight
of arborvitae in eastern states
and of giant arborvitae, sometimes called western
red cedar. The fungus is a native of North Amer-
ica and occurs abundantly in the West, damaging
seedlings and saplings, often killing trees up to
4 years old, if they are in dense stands in humid
regions. Older trees do not die, but foliage
appears scorched, particularly on lower branches,
and young leaf twigs may drop. Cushionlike,
olive brown apothecia embedded in leaf tissue,
usually upper, are exposed by rupture of the epi-
dermis. After summer discharge of spores (round,
brown, unequally two-celled) the apothecia drop
out of the needles, leaving deep pits.
