CropLand Security: Protecting Crops with Herbicide Safeners
|Dean E. Riechers
Associate Professor of Weed Physiology
Department of Crop Sciences
Herbicides are designed to selectively kill weeds in crops. For example, the sulfonylurea herbicide nicosulfuron (Accent) is designed to selectively control grassy weeds, such as giant foxtail, in corn. However, crops are often injured by herbicides due to stressful environmental conditions, differences in hybrid or cultivar tolerance, variability within or among fields in percent soil organic matter, or misapplication. In addition, it is difficult for herbicides to selectively control weeds that are closely related to crops (for example, shattercane and johnsongrass in corn or sorghum). Since herbicide selectivity between crops and weedy plants is usually based on rapid herbicide metabolism and detoxification by the crop, closely related weeds would be expected to have detoxification pathways similar to those in the crop.
Chemical compounds called herbicide safeners protect cereal crops such as corn, grain sorghum and wheat from herbicide injury. Although herbicide safeners are included with several commonly used soil-applied herbicides for corn, how and why safeners work in the crop plant is not well understood. Recent discoveries in my laboratory indicate that safeners trigger the expression of proteins in a plant defense pathway that is normally regulated by a plant hormone called jasmonic acid. This pathway is normally stimulated in response to insect feeding or by other types of stress, but it appears that the herbicide safeners also induce proteins and genes involved in a similar type of stress response within the same plant defense pathway.
One very interesting (yet unresolved to date) question that has baffled weed science researchers for decades is why herbicide safeners do not protect broadleaf crops, such as soybeans and cotton, from herbicide injury. Recent research shows that this might be due to differences in the tissues of an emerging grass and broadleaf crop seedling and how they respond to safener treatment. More specifically, grass crop seedlings have an organ called the coleoptile that protects the emerging new leaves from herbicide injury, whereas broadleaf crop seedlings do not have coleoptiles. This new information regarding how, why, and where safeners work in cereal (grass) crops has great potential for improvement of weed management systems by potentially introducing the safener response into broadleaf crops such as soybean through biotechnology. This would allow for the introduction of herbicides that currently are not registered for use in soybean due to unacceptable crop injury, and would potentially expand the number of weed management options for controlling resistant or difficult-to-control weeds such as waterhemp and lambsquarters.