Cylindrocladium black rot of peanutBarbara Shew
Updated June 17, 2011
Cylindrocladium black rot (CBR) in peanut is caused by the soil borne fungus Cylindrocladium parasiticum. CBR is present in all peanut production areas in North Carolina, although it is uncommon in fields that do not have a long history of peanut production. Without proper management, this disease can cause devastating losses.
Often, the first above-ground symptom
of CBR is wilting on hot afternoons in mid-to-late August. Later, the entire
plant may turn light green or yellow and eventually may die. Late in the
season, particularly following moist weather, the fungus may produce numerous
brick-red, pinhead-sized fruiting structures on crowns, lower stems, and pods of
The taproot of symptomatic plants is black and rotted. Lateral roots have similar symptoms, or may be missing entirely. The rotted roots are very brittle and infected plants often break off at the soil line when tugged. CBR also rots pods, resulting in heavy yield losses. Seeds that are not rotted often are covered with cinnamon-brown speckles. These speckles are microsclerotia (MS) produced by the fungus. MS also are produced inside the infected roots.
Factors that favor disease
The CBR fungus grows best in cool, moist soil and many root infections occur soon after planting. Root wounding from nematode infections increases severity of CBR infection. Root nodules, although desirable for nitrogen fixation, are very susceptible to infection.
Poor rotations are a major cause of CBR problems. The MS produced in roots of infected plants are released into the soil as the peanut residue decomposes. Repeated planting of peanuts or soybeans can increase the number of MS in soil, where they can survive for many years.
Rotations of three years or more
to non-hosts are necessary to prevent or reduce CBR problems. Cotton, corn, sorghum,
and small grains are not hosts of the CBR fungus and are excellent rotation
crops. On the other hand, the CBR fungus infects
soybeans, increasing populations of MS between peanut crops. On soybeans, the disease is known as red crown. Soybeans can be
infected without a grower being aware of the problem since symptoms of red crown often are less
severe than CBR on peanut.
Planting a resistant cultivar often is all that is needed to avoid CBR losses in well-rotated fields. The virginia-type cultivars Bailey and Sugg and several runner-type cultivars have high partial resistance to CBR. The cultivar Perry has moderate CBR resistance. Most other virginia types are susceptible. Avoid planting highly susceptible cultivars such as VA 98R and CHAMPS in fields with a history of CBR.
CBR can be seed transmitted, so always purchase fungicide-treated seed from a reputable dealer.
CBR can be confused to spotted wilt, so be sure to obtain a positive diagnosis if there is any doubt. Make a note of problem fields and attempt to estimate the percentage of plants with symptoms. This information will help with rotation, fumigation, and cultivar choices the next time peanuts are planted.
Fumigation with metam sodium may be necessary in fields with a history of greater than 10% disease the last time peanuts were planted. Fumigation works by killing MS in soil. Root knot and ring nematodes can make CBR problems worse and fumigation also provides some control of these nematodes.
Inject metam 42% at 7.5 gal/acre 12 inches below the top of the bed (or 8 inches below the original soil surface) at least 2 weeks before planting. Apply after soil temperatures reach 60 F at a 4-inch depth, and temperatures of 60 F or higher are forecast for the next 5 days. Rain can greatly diminish the effectiveness of fumigation, so wait to fumigate if an inch or more of rain is forecast within 3 days. Avoid disturbing the soil after fumigation or untreated soil could be mixed with the fumigated soil. Herbicides can be incorporated before bedding and fumigation. Special precautions are required by law when applying soil fumigants.