Biology Reference
In-Depth Information
pycnidia. All leaves on the plant may die except
a few at the top. Remove infected leaves as soon
as noticed. Spray with a copper fungicide.
Physalospora
first, later large bleached or scalded areas. Dark,
watersoaked patches on fruits are covered with
white mycelium. The fruit withers but remains
attached; 60 % of green fruit may be infected in
southwestern commercial plantings. Seed are
infected from the fruit. Symptoms on squash are
somewhat similar; green leaf lesions spreading
over the blade, a basal stem rot, and wilting. Wet
soil and high temperatures encourage blight.
Control
Place seedbeds on land that has not pre-
viously grown peppers; rotate crops. Avoid over
irrigation.
Phytophthora citrophthora (also
P. citricola
and
P. nicotianae
var.
parasitica
).
Shoot and
Stem Blight
on azalea.
Needle Blight
and
Branch
Dieback
of sequoia.
Phytophthora erythroseptica
Leaf Blight
of
pink and golden calla. Leaves are wilted and
distorted; petioles are black and soft.
Phytophthora ilicis
Holly Blight
,
Phytophthora Leaf
and
Twig Blight
, the most
serious disease of English holly, particularly seri-
ous in the Northwest. For many years the trouble
was ascribed to
Boydia insculpta
and called
Boydia canker, but this fungus merely invades
tissue killed by
Phytophthora
. Leaf spots are
dark, developing on lower leaves in cool rainy
weather and progressing upward in late fall and
winter. Young twigs die back; black stem cankers
kill older twigs. Young plants in nurseries are
defoliated and sometimes killed.
Control
Choose a planting site with moderate air
movement; space trees well apart. Prune out all
cankered and blighted twigs; prune also for air
movement through trees. Spray with tribasic cop-
per sulfate, starting the middle of October.
Phytophthora infestans
Late Blight
of potato
and tomato, general on potato in the Northeast, in
Middle Atlantic and North Central states, some-
times in Gulf and western states; on tomato in
humid regions and seasons. Here is a pathogen
that has not lost its destructive virulence with pas-
sage of time. In 1946, a whole century after potato
blight caused the famous Irish famine, tomato
blight devastated tomatoes along the eastern sea-
board, both in home gardens and canning fields.
The potato went to Europe from South Amer-
ica shortly before 1600, seemingly leaving its
Glomerella
cingulata
).
Dracaena Tip Blight
,
Leaf Spot
.
Physalospora gregaria
Twig Blight
of yew.
Physalospora obtusa (see
dracaenae
(
▶
Botryosphaeria
apple,
Canker
and
Dieback
of many plants.
▶
Phytophthora
Oomycetes, Peronosporales
This most important genus contains many species
causing destructive blights, cankers, and rots.
The name, which means “plant destroyer,” was
given in 1876 for the potato blight fungus.
Sporangia, formed successively on sporangio-
phores, slender, sparsely branched hyphae
emerging from stomata, germinate either by
a germ tube or by zoospores. The sexual spore
is an oospore.
Phytophthora cactorum
Lilac Shoot Blight
.
Blossoms and succulent growing tips are blighted
and turn brown; suckers are killed back 4 or 5
feet. Blight is most severe in wet springs when
shrubs are crowded, shaded, and improperly
pruned. The same fungus causes a canker, foot
rot, and dieback of rhododendron and other plants
and is considered again under Cankers. Avoid
planting lilacs and rhododendrons close together.
Prune each year for air circulation and to remove
dead twigs.
Phytophthora capsici
Phytophthora Blight
of
Pepper,
Leaf and Stem Blight
of Squash, Fruit
Rot of pepper, eggplant, tomato, cucumber, and
melon. The disease was first found in New Mex-
ico in 1918 injuring chili peppers; it occurs
chiefly in southwestern and Gulf states. In 1953,
however, it was reported that for some years it
had been causing a leaf blight of squash in North
Carolina.
Pepper plants are girdled at the soil line with
a dark green water-soaked band, which dries and
turns brown, followed by wilting and death of the
entire plant. Leaf spots are dark green and small at
