White Mold - Management

Soybean stems with evidence of lesions caused by the whilte mold pathogen. Click on image to view larger version. Photo credit: Craig Grau, University of Wisconsin

Choose management practices that both reduce the risk of white mold and maximize soybean yield when white mold is present.

Variety Selection

Variety selection is the most important component of a white mold management plan. Plant varieties that are short and do not tend to lodge.  Although there is currently no soybean variety completely resistant to white mold, the use of tolerant varieties is effective in managing white mold and maintaining yield potential. Avoid planting highly susceptible varieties in fields with a history of white mold.
Read more about variety evaluation and selection»

Canopy management

Production practices designed to increase yields promote fast and complete canopy closure, which results in a favorable environment for white mold. Base your canopy management on the history of white mold and other risk factors as outlined in the table below.

Row spacing
White mold increases as row spacing is narrowed in low to moderate disease pressure environments. However, under high disease pressure, white mold severity is similar among wide and narrow row widths.

Yield is highest if a partially resistant (most resistant variety available) variety is planted in a narrow row system. Soybean yields in the presence of moderate to severe white mold in 1998 and 1999 were higher for 15-inch row width when compared to 7.5 and 30-inch row width systems. Variety selection is critical to maintain yield potential in the presence of white mold.

Table 1. Canopy managment recommendations based on the field history of white mold.

Field History	Variety Selection	Canopy row width and plant density	Crop Rotation	Agricultural Chemicals
				Grain Fields	Seed Fields
No white mold Monitor fields closely	Variety of choice; plant pathogen free seed	Maintain current row width and plant population	Avoid crops susceptible to white mold	Adjustments to herbicide program not needed	Adjustments to herbicide program not needed
<5% diseased plants aggregated in field	Avoid susceptible varieties	Maintain current row width and plant population	Minimum of 1 year out of soybean	Adjustments to herbicide program not needed	Adjustments to herbicide program not needed
<5% diseased plants uniformly distributed in field	Consider partially resistant; avoid highly susceptible varieties	Maintain current row width and lower population for less resistant varieties	Minimum of 1 year out of soybean	Adjustments to herbicide program not needed	Adjustments to herbicide program not needed
5-25% diseased plants	Partially resistant varieties	Maintain current row width and   plant population	Minimum of 1 year out of soybean	Adjustments to herbicide program not needed	Adjustments to herbicide program not needed
5-25% diseased plants	Moderately susceptible varieties	Widen row width and lower plant population	Minimum of 1 year out of soybean	Consider white mold suppressive herbicides	Consider white mold suppressive herbicides or fungicides
25-50% diseased plants	Partially resistant varieties	Maintain current row width and lower plant population	1 to 2 years out of soybean	Adjustments to herbicide program not needed	Consider white mold suppressive fungicides
25-50% diseased plants	Moderately susceptible varieties	Use 30 inch row width. Plant    <180,000 plants/acre	1 to 2 years out of soybean	Consider white mold suppressive herbicides	Consider white mold suppressive herbicides or fungicides
>50% diseased plants	Partially resistant varieties	Use 15 to 30 inch row width. Plant <180,000 plants/acre	2-3 years out of soybean	Consider white mold suppressive herbicides	Consider white mold suppressive herbicides or fungicides

 

Irrigation

Avoid excessive irrigation until after flowering.

Tillage

Tillage affects white mold in several ways. Although sclerotia can survive in deep soil up to 7 years, only sclerotia within 2 inches from soil surface germinate and produce spores to infect soybean. Therefore, burying infested residues by deep plowing can prevent the germination of the sclerotia. However, subsequent cultivation and tillage would bring sclerotia up to the surface.

Under no-till, or shallow till, a large portion of the sclerotia germinate under corn or other nonhost crops, which reduces the amount of pathogen in the soil. Recent research from Iowa State University shows that in long-run, no-till results in a smaller white mold risk compared with conventional tillage

Weed control

The white mold fungus infects common weeds like lambs-quarters and pigweed. Use good weed control practices, especially in rotation years.

 

Some sclerotia (dark, fungal overwintering structures) are similar in size to soybean seed.

Minimize spread between fields, especially during harvest

An important method of controlling white mold is to minimize the spread of the fungus between fields. It can be spread with seed, equipment, manure, and movement of soil. Sclerotia are present in soybean stems and debris, which can be carried by harvest equipment between fields during harvest. When combining a soybean field infested with white mold, harvest the diseased patches last so that the combine will not spread infested plant materials to non-infested areas.

Some sclerotia are similar in size and shape to soybean seed. Therefore, a combine can not completely separate sclerotia from the seed. Use of seed mixed with sclerotia will spread the pathogen from one field to another. However, if seed lots are contaminated, they can be cleaned of sclerotia by gravity tables and spirals.

 

Harvesting

Prevent spread of the white mold fungus from field to field by harvesting fields with white mold last. If the disease is present in one or two patches in a field, harvest these areas last, which can help prevent the spread of infested crop debris to other parts of soybean field. If this is not feasible, clean debris from combines after harvesting fields or patches infested with white mold.

 

Crop rotation

Short crop rotations, such as a soybean-corn rotation, will eventually lead to a build up of sclerotia in the field. Sufficiently long crop rotations with corn and wheat (both nonhosts) will be effective in minimizing the pathogen buildup and risk of white mold outbreak. Most sclerotia die over a three- to four-year period between soybean crops.

The risk of white mold is even greater if other host crops are grown in rotation with soybean. Avoid planting soybean directly after common bean, sunflower, and other susceptible crops.

Some sclerotia are similar in size and shape to soybean seed. Therefore, a combine can not completely separate sclerotia from the seed. Use of seed mixed with sclerotia will spread the pathogen from one field to another. However, if seed lots are contaminated, they can be cleaned of sclerotia by gravity tables and spirals.