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.
|
|
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 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.
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 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, beginning in late July until digging.
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 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 70’s or above and periods of high humidity, spores of the fungus can be observed on mature lesions.
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.
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.
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.
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.
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.