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Strong soybean disease management, including timely scouting when flowers first appear (R1), will be critical for soybean farmers this growing season as they grapple with increasingly prevalent soybean white mold in the Midwest.

Compared to previous years, white mold—or Sclerotinia Stem rot—was more common in 2015 and surfaced in many farm fields to some degree. Historically, soybean fields in Northern Illinois have been hardest hit by the destructive disease because that area has more of the cool, wet weather that promotes fungal growth than does the southern part of the state.

Timing is everything when it comes to white mold, with the plants especially susceptible in the R1 and R2 stages. Blossoms typically are the first part of the plant to be colonized. Pale lesions enlarge and within days become blanketed with a fluffy, white fungal growth. The environmental conditions at this point of flowering are critical.

Watch for disease triangle
Be vigilant for a nasty triangle that creates conditions for any disease, including white mold. The disease must be present, the plant must be susceptible, and environmental conditions of cool, wet weather must exist. In addition, corn residue left in fields and reduced tillage foster this destructive fungus, which can slash yields.

Use multiple management practices to control white mold. Choose the most-resistant varieties. Use recommended seeding rates. Apply a foliar fungicide and a biocontrol product.

Arming for wars on spores

There are new products on the market to combat white mold:

1. Consult seed specialists before choosing resistant varieties and seed treatment packages. Consider some of the super strains of Rhizobia.
2. In fields with a history of white mold, plant wide rows 30 inches apart with lower density, so air circulates through the canopy.
3. Use fungicide applications when the plant begins flowering in R1, and again at R2 or R3 stages. Check product labels for application requirements.
4. White mold signs appear two or more weeks after flowering, with wilting and dead upper leaves. Farmers should scout for lesions with white, cottony and thick fungal growth just above the soil surface.
5. Use mapping technology to spot stressed and low areas in fields, and avoid planting there. Farmers can use historical maps to build a data set and do population studies.
6. Farmers should do the population trials in fields with a history of white mold to determine optimum plant population. Farmers could make a couple of passes at 70,000 seeds per acre, a couple at 90,000 and go up to 150,000 in different spots in fields. Even without a variable-rate planter, a farmer can adjust seeding rates.

Remember to consult your 2015 yield monitor results to see which areas of your fields had disease pressure. This can help you see how to optimize population and reduce disease impact.

Dr. Bob Beck is a WinField agronomist out of central Illinois. Feel free to contact him with any questions at rhbeck@landolakes.com.