Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu
Snap beans and lima beans are at risk of white mold when the soil has been wet for 6 to 10 days before bloom. For snap beans, a fungicide should be applied when the plants are at 10 – 20% bloom, and followed with a second spray in 7 to 10 days if soil remains wet. Prolonged soil moisture also triggers white mold in lima bean, however later applications of fungicide (post bloom) have been beneficial to lima beans because they are a longer season crop.
Both snap and lima beans can be sprayed with the following:
● Endura 70WP at 8-11 oz/A (This was the most effective fungicide in my lima bean trials.)
Other effective fungicides are:
● Rovral 4F at 1-2 pts/A
● Topsin M 70WP at 1.5 to 2 lb/A
● Switch 62.5WG at 11-14 oz/A
The following may be used for snap beans only:
● Endura 5 oz/A plus thiophanate-methyl at 0.7-1.05 lb/A active ingredient
● Topsin M 70WP at 11.2 oz/A plus chlorothalonil 6F at 1.5 pts/A
● Switch 62.5WG at 6-11 oz/A plus thiophanate-methyl at 0.7-1.05 lb/A active ingredient
White mold on snap beans or lima beans is characterized by dense white cottony growth. All plant parts can be infected as the fungus grows from initial infection of flowers and pins to stems and leaves.
When white mold infection is advanced the fungus produces hard black overwintering structures called sclerotia. The presence of these confirms the presence of white mold.