Southern stem rot of peanut
Updated June 17, 2011
Southern stem rot of peanut is caused by the soil borne
fungus Sclerotium rolfsii. The disease is also known as stem rot or
white mold on peanut and as southern blight on vegetables. Southern stem rot
and S. rolfsii are very common and can be found in most peanut
fields in North Carolina. Damage ranges from mild to severe.
Symptoms of southern stem rot include wilting of
individual stems, stem lesions, shredded stems and pegs, rotted pods, and plant
death. Stem lesions and pods are similar in color to a brown paper bag. Coarse
white strands of the fungus growing in a fan-shaped pattern may be present on lower stems,
leaf litter, or soil (Figure 1). Later, tan to brown sclerotia that look like mustard seed
may be present (Figure 2). The signs of the fungus are diagnostic of southern stem rot,
but damage can occur even when these signs are absent. (video)
Conditions that favor the disease
Fields with heavy vine growth and high moisture are most
prone to stem rot. This disease is most active during the hottest part of the
season, especially following rain. In drier seasons, the fungus is most active
underground, causing stem and pod damage that may not be noticeable until
digging (Figure 3). Southern stem rot often is found together with CBR.
Sclerotium rolfsii has an extremely broad host range, but it does not attack small grains, corn, and other grass species. Rotations with these crops will help to reduce stem rot problems. Avoid rotations with soybeans, tobacco, melons, and vegetables.
Some fungicides used to control leaf spots also control
southern stem rot. Using a soil fungicide as part of a leaf spot control
program is beneficial in most fields. Examples include azoxystrobin (Abound),
pyraclostrobin (Headline), tebuconazole (Folicur and generic brands), and
prothioconazole + tebuconazole (Provost). However, control may require
higher rates than those used for leaf spot control. Flutolanil (Convoy or
Artisan) controls southern stem rot but not foliar diseases, so a leaf spot
control program is necessary with this fungicide. See the North Carolina Agricultural Chemicals Manual for labeled fungicides and rates.
Most soil fungicides work best when applied just before disease onset. Make at least 2 applications of a soil fungicide according to the leaf spot advisory or calendar schedule between July 15 and the end of August. High spray volumes (20 gal/a) and spraying when leaves are folded (before dawn) can increase fungicide deposition on stems but may make foliar disease control less effective.