Herbicide resistant weeds becoming bigger problem in Brazil

Soybean farmers in Brazil are becoming more concerned about invasive weed species in their soybeans fields, especially herbicide resistant weeds such as pigweed. Pigweed has become one of the principal weed problems in southern Brazil and it continues to migrate northward in Brazil. Scientists believe there are several million hectares in southern Brazil where herbicide resistant pigweed has become a significant problem. No herbicide resistant pigweeds have been found in the state of Mato Grosso, but researchers in Brazil feel it is just a matter of time before farmers in the cerrado regions of central Brazil will be confronted by this difficult to control weed.

Pigweed is a prolific seed producer, which makes it very difficult to control. A single plant can produce up to 200,000 seeds that can be easily dispersed by the wind. An individual farmer may do a good job in controlling the weed on his property, but if his neighbor's field has inadequate control, he could end up with the problem as well. In order to keep the weed at bay, it needs to be controlled not only in soybean fields, but also along highways, in the fence rows, and in nearby pastures as well.

The widespread use of Roundup Ready soybeans and Roundup herbicide has led to the development of herbicide resistant weeds. These resistant weeds have become an economic concern for farmers because three or four pigweed plants per square meter can result in crop losses of up to 10%. If the infestation is worse, the losses are greater. In extreme cases where no control measures are used at all, losses can be as high as 80%.

Weed control in the soybean fields of Brazil was easier in years past because of a general lack of invasive weed species, but after several decades of mono crop soybean production and the use of a single herbicide, weed control in Brazilian soybean fields has become more difficult and more expensive. For many years farmers only had to use Roundup herbicide to have adequate weed control, but with the advent of Roundup resistant weeds, farmers have been forced to apply a cocktail of herbicides to keep the weeds under control. This has increased their production costs and increased the complexity of their weed control measures.

Farmers in central Brazil have an additional problem because there are no freezing temperatures to kill any escaped weeds during the off season. Temperatures during the dry season are very warm allowing for weeds to grow year round along the edges of the fields and in nearby pastures. As a result, scientists urge farmers to control the weeds all throughout the year not just during the growing season.

Pigweed is much easier to control when the plants are small. Attempting to control full-sided plants can be very difficult, so every effort must be made to control the plants while they are small. The cost of control measures may equal to 0.7 sacks of soybeans per hectare or about half a bushel per acre. Adequately controlling the weed though could save as much as 4-5 sacks per hectare in lost production or approximately 3-4 bushels per acre.