EPWS
310 - PLANT PATHOLOGY
Readings: Pages 473-500
Southern corn leaf blight - Cochliobolus
heterostrophus (teleomorph) and Bipolaris (anamorph)
Causes small tan leaf lesions which may be
numerous enough to cover the leaf. The head and ears may also be affected
resulting complete loss. The susceptible Texas cytoplasm from race
"T" caused the loss of 15% of corn in early 1970's.
Resistance has kept the disease under control
but it is widespread.
LIFE CYCLE - Fig. 11-63
Overwinter as conidia and mycelium in plant
debris.
Control by resistance and sanitation,
rotation and proper break down of plant debris. The fungi do not survive well
in intimate contact with soil. So plow the debris in!
SOIL INVADERS v.'s SOIL INHABITANTS
Systemic fungicides as Imazalil, Nuarimol and
Fenapenil work well for both the foliar and root phases of these diseases.
CANKER
AND ANTHRACNOSE DISEASES
Nectria
canker diseases
Ascomycete Anamorph is Fusarium and Cylindrocarpon.
Major disease of apples and pears and forest
hardwoods.
Cankers girdle the tree and can kill saplings
while lopping branches off older trees.
These are necrotrophic and enter through
wounds and bud scars. The spores are dispersed by rain and insects.
Typified by callus growth and target shaped
cankers.
LIFE CYCLE - Fig. 11-70
Conidia formed on sporodochia and
overwintering as mycelium in dead bark and callus tissue and as perithecia in
bark.
Ascospores are abundant in late fall.
Control: Sanitation and burning of affected
limbs and fungicide application after leaf fall reduced inoculum in orchards.
ANTHRACNOSE
DISEASES CAUSED BY COLLETOTRICHUM
There are many anthracnose fungi but the most
common and important is Colletotrichum anamorph of Glomerella.
These form a complex of diseases of many crops and ornamentals - Rose,
strawberry, grape, raspberry, citrus, apple soybean, banana, cotton, hickory
etc etc.
Including the Diplocarpon black spot
of rose.
Generally a problem under humid conditions
cool to warm, often bad in greenhouses.
The diseases often affect young tissue,
leaves, shoots, flowers etc.
They are often seedborne.
They are unusual fungi in that the early
stages of infection are biotrophs and then necrotrophs. Often with latent
infection.
Colletotrichum affects cucurbits,
tomato, cereals, grasses, banana, onion and citrus.
LIFE CYCLE Fig. 11-84
Favored by warm humid conditions.
Control depends on disease free seed and
sanitation, some resistance is available. Fungicides applied as control and
postharvest.