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August 7, 2013

Cyst Nematodes are Increasing Problem for Brazil Soy Producers

Nematodes have long been a problem for American soybean producers and they are now becoming a bigger problem for Brazilian soybean producers as well. The microscopic worms penetrate the soybean roots making it difficult for the plant to take up water and nutrients.

Light infestations can be seen in the field in the form of a circular pattern of yellowish plants. Under average levels of infestation, the pests can reduce yields by at least several bushels per acre. With severe infestations, the plants can actually be killed by the worms. Cyst nematodes can be a hidden yield robber because there may not be any visible signs of infestations.

Cyst nematodes were discovered in Brazil during the 1991/92 growing season and have since been found in most soybean producing regions of the country. They can be spread from field to field by tillage equipment, planters, combines, and seed. There are multiple races of cyst nematodes and final confirmation of the type of nematodes present in a field can only be accomplished with a soil analysis.

In areas where cyst nematodes have been confirmed, the farmers must learn to live the pests because eradication is nearly impossible. The two best ways to minimize loses are with crop rotations and planting soybean varieties that are resistant to the predominate races in the field. Over the years, one of the main goals of soybean breeders has been to develop varieties resistant to the predominate races of nematodes, but their efforts turn into a perpetual "arms race" between the breeders and the pests. As soon as resistant varieties are developed to the predominant races, the worm mutates into new races and overcomes the resistance.

Scientists have learned over the years that if only resistant varieties are planted it speeds up the mutation process of the worms. Therefore, they recommend to farmers to plant a susceptible variety every four years to slow down the mutation process. It is hard to convince farmers to sacrifice some of the potential soybean yield every four years to satisfy the worms, but it is best in the long run if they want to hold down the number of races of nematodes.

Another way to control the pest is to regularly rotate out of soybeans to other crops for at least one growing season. Corn is the best crop to rotate with soybeans, but planting a second crop of safrinha corn after soybeans does very little to help control the pest. If soybeans are planted in the field every growing season and the corn is only planted following the soybeans, that is insufficient to control cyst nematodes. Adequate control is only achieved if soybeans are not planted at all during at least one growing season.

The pests do not feed on corn roots, so pest populations tend to crash if soybeans are not present in a field for at least a year.