White Mold
White mold is a key pest of dry beans in Michigan. White mold infections initiate at the flowers and enter the stem. Stem infection causes that part above the point of infection to wilt and die. Affected stems appear bleached and dry which differs from the tan color characteristic of mature, dry plant tissue.

Certified seed of recommended bush or upright type varieties is planted if land has a history of white mold. Rotation for at least three years to non-host crops such as sugarbeets, corn, sorghum, barley, and other small grains is recommended to reduce the number of white mold sclerotia. Growers use recommended plant populations and row widths to promote rapid drying of the plants and soil surface after rain or irrigation, especially immediately before and during the flowering period. Apply only the recommended amount of fertilizer where needed to avoid excess canopy development. Irrigation is scheduled only as required by the crop for satisfactory growth since disease development depends on a moist soil surface beneath the plant. Late in the season the only way to slow down a white mold epidemic is to extend irrigation intervals or cease irrigating.

Because white mold is not a problem every year, but only when there is abundant rainfall and an extensive canopy cover, chemical control may not be advisable as a normal management practice. However, chemical control can be effective when the chemical is applied before the infection has occurred or if the chemical adheres to the plant for a considerable period of time. Chemical applications can also be effective if the chemical penetrates the canopy and reaches the flowers, which are the most important sites of initial infection. These conditions require that the timing of sprays be adjusted so that a maximum number of flowers are protected by a chemical that moves into the canopy before the canopy closes. Spraying is done between the onset of flowering and peak bloom. The timing of chemical applications is critical.

White Mold Sclerotia
Hard, black, irregulary-shaped resting structures (sclerotia) of the fungus form on and within the infected plant parts. Sclerotia which fall to the soil during harvest, germinate the following season as small (1/4 inch or 6 mm diameter) beige-colored mushroom-like structures (apothecia) which release spores that are spread to dead blossoms or leaves. These spores germinate on and utilize this dead tissue as an energy source before the fungus invades healthy tissue.