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December 6, 2013

Volunteer Corn Becoming Problem in Brazilian Soybean Fields

Brazilian soybean farmers have a lot of things to worry about during the growing season such as the weather, corn earworm, soybean rust, white mold, nematodes, etc. They can now add one more thing to their list of worries and that is volunteer corn growing in their soybean fields. This has become a larger problem in recent years because more of the corn being grown in Brazil is now Roundup Ready, which means that the Roundup herbicide used to control weeds in the soybean fields will not eliminate the corn.

According to a researcher at Embrapa Soja, Fernando Adegas, the problem has become more important in areas where Roundup Ready corn is planted as a safrinha crop after Roundup Ready soybeans have been harvested. The safrinha corn is planted in January or February and harvested during the dry season (June and July). Any kernels that fall onto the ground during harvest probably won't germinate until the rains return in September. That is also when farmers start planting their next soybean crop, so both the Roundup Ready soybeans and corn germinate at the same time.

Embrapa research indicates that 2 to 4 corn plants per square meter could result in soybean yield reductions of up to 50%. In addition to the potential for lower yields, controlling the corn requires the use of more expensive grass herbicides to solve the problem.

Researchers point out that it's best to try to control the volunteer corn shortly after emergence when the young corn plants are more easily eliminated. One of the problems though is that the corn may not germinate uniformly which could require more than one herbicide application. Ultimately, the best way to minimize this problem is to reduce as much as possible the amount of harvest loss during the corn harvest.

Volunteer plants from the previous crop can also be a problem when safrinha cotton is planted after soybeans. In that case, the problem is volunteer soybeans in the midst of the cotton field.

The entire problem of volunteer crops is symptomatic of the cropping patterns in Brazil. In the tropical climate of central Brazil, germinating plants from the previous crop can easily appear in the next crop especially when two crops are planted back-to-back in the same field in rapid succession. This is especially problematic when both crops are Roundup Ready varieties, which forces the farmers to switch herbicides if they want to control the problem.

Farmers in the United States rarely encounter this problem because the cold winter temperatures usually eliminate the volunteer corn. Farmers in Argentina typically do not plant a second crop of corn or cotton after soybeans either so they do not have the problem. The primary double crop sequence in both the U.S. and Argentina is to plant soybeans after the wheat is harvested and any volunteer wheat in the soybean fields usually is of minor consequence.