In most years, the first symptoms of Cylindrocladium black rot (CBR) are seen in mid to late July. Initially, infected plants appear stunted and exhibit yellow foliage that wilts on hot days. As the season progresses, these plants will eventually collapse and die. The distribution of diseased plants in fields may be localized to small areas or vary widely to encompass an entire field.
A useful diagnostic sign of Cylindrocladium black rot (CBR) is the occurrence of small, reddish-orange, spherical bodies (perithecia) of the fungus in dense clusters on stems, pegs and pods just above and/or below the soil surface. These structures are generally easy to find on diseased tissues following wet weather or in moist areas of fields. If these structures cannot be found on diseased plants in the field, tissue samples must be assayed in a laboratory in order to identify the disease as CBR.
Cylindrocladium black rot can result in complete destruction of the peanut root system and pods. Pulling infected plants will expose the blackened and severely rotted taproot, lateral roots and pods. The taproot of wilted and/or dead plants will usually be completely destroyed except for a small stub below the crown of plants. Pods may show various stages of decay ranging from black spots to complete black coloration and decay. Decay of pegs results in shedding of peanuts prematurely and the occurrence of high numbers of volunteer peanuts in the following year's crop.