Sclerotinia blight’s initial symptom includes a rapid wilting
or flagging of the tips of infected branches. Initially, lesions
are small, light green and water-soaked. As the disease develops,
the lesions turn light brown, elongated, and appear sunken. Older
lesions may be dark brown with a distinct border between diseased
and healthy tissue. Another symptom of infected plants is the presence
of shredded tissue (pegs and branches). The fungus produces white,
fluffy fungal growth on diseased tissue when humidity is high. As
the disease progresses, the fungus produces large black sclerotia
on and in infected plant tissue.
LATE LEAF SPOT
Late leaf spot symptons are similar to those of early leaf spot,
but lesions are usually dark brown to black. Conditions for disease
development are the same as for early leaf spot. During favorable
conditions, spores of this fungus can be seen on the underside of
the leaf. Under extreme pressure, lesions can develop on stems.
Given its wide range of symptoms, spotted wilt disease is sometimes
confused with white mold and CBR. Spotted wilt is a viral disease
spread by thrips. Foliar symptoms can be one or more of the following:
concentric light green to yellow ringspots (predominant on young foliage),
chlorosis (yellowing), necrotic terminals and/or necrotic leaf spots,
nondescript tan spots or blotches, oakleafing or streaking, and mottling.
Foliage of infected plants may be reduced in size. Plants infected
early in the season are usually stunted, have reduced pod production,
and may die.
Rust is readily identified by the presence of numerous orange-to-
red-colored lesions (pustules) on the underside of the leaf. Each
lesion contains many orange- to red-colored spores. Typically, leaves
of infected plants remain attached. Infected areas in fields may
have a scorched appearance.
STEM ROT OR WHITE MOLD
Stem rot or white mold is favored by hot, wet weather. Initially,
foliage of the infected plants is chlorotic; this may include the
whole plant or be limited to a branch. As the disease develops,
the foliage turns brown to black. The crown area is usually light
to dark brown depending on the stage of disease development. Symptoms
unique to stem rot are white strands of fungus and white to brown
sclerotia. These are usually found in the crown area of infected
plants. Fields where stem rot is suspected should be scouted late
in the season, 24 to 48 hours after a rain or irrigation event,
beginning in late July until digging.
NORTHERN ROOT-KNOT NEMATODE
Northern root-knot nematode symptoms are the same as those described
for peanut root-knot nematode. Galls are usually smaller than those
caused by the peanut root-knot nematode and limited to the roots.
The root system of infected plants will be dense and bushy.
EARLY LEAF SPOT
Early leaf spot lesions are initially very small and light
brown in color. Under favorable conditions, lesions enlarge (up
to 1/2 inch in diameter) and are usually surrounded by a yellow
halo (halo not always present). Lesions may be evident within 10
to 14 days after infection. During or after periods of warm temperatures
in the 70s or above and during periods of high humidity, spores
of the fungus can be observed on mature lesions.
Web blotch lesions are characterized as having a netlike or webbing
pattern which is purplish, brown to tan on the upper leaf surface.
Circular, tan to brown lesions may also be observed on the upper
leaf surface. Lesions may grow together to cover the entire leaf.
Older lesions are usually dry and cracked.
RHIZOCTONIA LIMB ROT
Rhizoctonia limb rot symptoms are usually not noticed until after
digging. Infected branches that were in contact with the soil are
black and rotten. Infection often starts near the tip of a branch,
killing the tip and then progressing down the branch.
Cylindrocladium Black Rot (CBR) infected plants are initially chlorotic
with foliage becoming brown to black as the disease develops. The
symptom unique to CBR is the presence of brick red reproductive
structures growing from the crown of infected plants. The crown
of infected plants is usually black. Root systems of severely infected
plants are deteriorated, void of secondary roots, and black. Infection
occurs at planting during cool, wet weather; however, symptom expression
does not occur until mid-July.
PEANUT ROOT-KNOT NEMATODE
Peanut root-knot nematode infected plants are usually stunted and
chlorotic. Typically, injury is not uniform in the field. Infected
areas in a field are typically circular. Roots, pegs and pods of
infected plants are galled. Galls on pods are wart-like in appearance
and dark in color.
DIPLODIA COLLAR ROT
Wilting and death of lateral branches or the entire plant
are symptoms of Diplodia collar rot that could easily be confused
with symptoms of other diseases. Elongated dead lesions with light
brown centers and dark brown margins may occur on stems. Fruiting
bodies of the fungus appear as small black dots embedded in the
infected host tissue. Collar rot is sporadic in occurence, but can
cause severe losses when an outbreak does occur.