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White Mold of Dry Beans
White mold can be severe if wet weather occurs prior to and at flowering time. The white mold fungus produces airborne spores if wet weather occurs for 1-2 weeks before flowering. The spores infect blossoms if they stay wet for 2 days. If white mold is severe, yield may be reduced by 300-1000 lb/A.
Dry beans should not be planted more often than every 3 years. Avoid rotation with other crops that are highly susceptible to white mold, such as sunflower and canola.
If a dry bean field has a yield potential of 2000 lb/A or more, white mold is a common problem in the general area, and weather has been wet for 1-2 weeks before flowering, it probably will be economic to apply a fungicide. Benlate and Topsin M provide good control if applied at early bloom. It is essential to provide good coverage of the entire plant, particularly the blossoms. The most effective and economical method of control is the use of drop nozzles between the rows and a pressure of at least 60-100 psi. Using drop nozzles it is possible to make a band application. The full rate is used in the band, but the band need be only about half the width between rows. Rovral can also be used for white mold. Rovral breaks down rapidly when the pH of the spray water is above 7.0. If Rovral is used, the pH of the spray water should be adjusted any time it is above 7.0.
If band application cannot be accomplished, use of a high pressure broadcast spray can be effective, although it is somewhat less effective than use of drop nozzles. Air assist spray units can provide canopy penetration that is equal to that from the use of drop nozzles. Aerial application can be effective if 7� gal/A is used and the boom is 6-8 feet above the canopy.
If a fungicide is to be used for white mold control, application at early bloom is essential. The white mold fungicides are much more effective in preventing infection than they are in curing infection.
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