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April 21, 2015

Volunteer Corn Becoming more of a Problem in Brazilian Soy Fields

The cropping sequence in Brazil is resulting in a unique set of problems for Brazilian farmers that are generally not seen in the U.S. or in neighboring Argentina. The presence of volunteer corn in soybean fields seems to be an increasing challenge for Brazilian farmers.

Much of the corn in Brazil is planted after the first crop of soybeans are harvested. This safrinha corn is generally planted in February or March and harvested in June or July. When the corn is harvested in central Brazil it is the dry season so any kernels of corn that may fall on the ground during harvesting will generally lie in dry soil until the rains return in September or October. That means the corn will germinate at the same time as the newly planted soybeans.

The problem is that over 90% of the soybeans grown in Brazil are Roundup resistant and much of the corn is also resistant to Roundup herbicide. It is difficult to control the volunteer corn because it is resistant to the preferred herbicide which is Roundup. This problem is generally not a serious threat in the United States because freezing temperatures during the winter eliminates most of the viable corn kernels. In Argentina, it is not a serious problem either because farmers in that country generally do not plant a second summer grain crop after soybeans.

If the volunteer corn is not eliminated, it will compete with the soybeans and Embrapa researchers have determined that the presence of two or three corn plants per square meter could result in soybean yield losses of up to 50%. If volunteer soybeans germinate in the following safrinha corn crop, it is not nearly as serious of a yield threat as vice versa. Volunteer soybeans though could harbor diseases such as soybean rust during the off-season and they need to be eliminated as well.

Researchers advise farmers to be as efficient as possible during the safrinha corn harvest to minimize the number of corn kernels that fall on the ground. When the corn germinates with the onset of the rains, they advise controlling the corn with a herbicide that has a different mode of action than Roundup and to control the corn when it is in the second or third leaf stage. Trying to control the corn at a later growth stage becomes more difficult.