Disease: Applying Cobra Herbicide to Soybeans for White Mold Prevention

Will applying Cobra® Herbicide really protect soybeans against white mold? That is the question that I and my fellow high-yield soybean enthusiasts set out to answer in 2009. Little did we know at the time that this would become the perfect year for this experiment. The field in question was moderate in fertility and did have a history of white mold.

• The beans were planted on May 20 and got off to a good start. We sprayed a residual pre-emerge herbicide on them and there was no weed competition to speak of.
• When the beans got to the R1 growth stage we were ready to make the application.  Also at that time, there were weeds present in the field.
• We sprayed the planned trip of glyphosate on the field and added 6 ounces per acre of Cobra Herbicide to the mix.  The application was made on July 13.

The soybeans in the treated and the untreated area remained similar in appearance for a while. But during routine scouting on September 4, large pockets of white mold appeared all of a sudden in the untreated area of the field. The difference in disease presence became greater and greater as the season moved on.

This picture taken in late September says it all. You can see the large pockets of white mold in the untreated side of the field.

Here is the yield map for the same field showing the 8-bushel difference in the treated versus the untreated soybeans.

All in all, the treatment of Cobra was very successful. The cost of the Cobra was only about one bushel per acre and the white mold reduced yields by an average of 8 bushels per acre.

Some things to keep in mind before making a decision to apply Cobra are:

• Cobra does not protect against all diseases.
• Cobra will burn and bronze soybeans and may be hard to look at for a couple weeks following application.
• Cobra at the six ounce rate is not a sufficient herbicide program by itself.
• Cobra must be applied before the onset of disease, it will have no effect if the soybeans are already infected with white mold, even if no symptoms are present.

If your fields have a history of white mold, or you think the weather this year is going to be conducive to white mold, Cobra Herbicide might just work for you.

Jeff Keifer
District 2