Posted 24 August 2009. PMN Crop News.
White Mold in Soybean
Source: University of Illinois Press Release. aces.illinois.edu
Urbana-Champaign, Illinois (August 12, 2009)--White mold, also known as Sclerotium stem rot, was found in a soybean field at the Western Illinois University Farm by Loretta Ortiz-Ribbing, University of Illinois Extension Specialist for Crop Systems. Conditions for development of this disease are wet, humid weather with below average temperatures of less than 83-85 degrees F. Nights and mornings with heavy dew and recent rainfall, along with the cooler temperatures of past weeks have caused ideal conditions for this disease to show up in soybean fields, says Ortiz-Ribbing. More information on white mold's disease cycle and management practices can be found in The Bulletin (July 24, issue 18, No. 8) on line at ipm.illinois.edu/bulletin.
Symptoms of white mold often appear on the foliage. Since this fungal disease effectively girdles the stem, the first foliar symptoms you may observe on plants in the field are wilting or upper leaves turning grayish-green. Eventually, the upper leaves of the plant turn brown and dry. Infected plants may be leaning over if the girdled part of the stem contains weakened dead tissue.
However, the most characteristic symptoms appear on the soybean stem. If you observe isolated spots in the field with lodged soybean plants whose top leaves are brown, dried, and shriveled, spread the canopy and examine the stems. Look at the mid to lower stem section for the characteristic white, fuzzy, cotton-like growth which is the fungal mycelium of this pathogen. The white mycelial growth will develop as long as moist, humid, and moderate temperature conditions persist, but it could disappear during hotter, dry conditions. Splitting open the stem will reveal dark brown to black sclerotia that resemble large mouse droppings, filling the empty stem cavity. The sclerotia are the survival structures for the fungus that persist in plant residue and soil.
The soybean field where white mold was discovered in Western Illinois was planted May 19th. The beans are about 36 to 40 inches tall and have almost complete canopy closure. Scouting your soybean fields will help determine if white mold is present when weather conditions favor its development. Management is difficult and requires integrating a variety of tactics. In his July 24, 2009 Bulletin article, Dr. Carl Bradley provided several management strategies which include cultural practices, as well as chemical and biological products.