Soybean injury from soil-applied herbicides
Integrated weed management programs offer the greatest potential for long-term, sustainable solutions to weed populations demonstrating resistance to herbicides from multiple families. Soil-residual herbicides are important components of integrated weed management programs and provide several benefits, including reducing the intensity of selection for resistance to foliar-applied herbicides. Recent survey data indicate the percentage of Illinois soybean acres treated with soil-residual herbicides has increased during the past few years.
In the vast majority of instances, soil-applied herbicides control target weed species with little to no adverse effect on the crop. However, soybean plants sometimes are injured by these herbicides. Questions about soybean injury caused by soil-applied herbicides recently have been posed, so this article will review some of the factors that can contribute to herbicide-induced soybean injury.
Herbicides vary in their inherent potential to cause soybean injury. Many university-generated herbicide effectiveness rating tables also provide estimates of soybean injury potential. Some herbicide active ingredients, such as cloransulam and clomazone, are often rated as having very low potential to cause soybean injury, whereas other active ingredients are rated as having a greater inherent potential to cause injury. The rate at which the herbicide is applied can influence the potential for soybean injury by increasing or decreasing the amount of herbicide in a given volume of soil.
Most many cultivars are not overly sensitive to any particular herbicide, but other soybean cultivars can vary in their sensitivity to certain herbicides. Data in the scientific literature and company-generated variety trials demonstrate cultivar sensitivity differences to various soil-residual herbicides. Some cultivars demonstrate sensitivity to one active ingredient, whereas other cultivars can be sensitive to more than one active ingredient.
The environment has a large influence on the severity of soybean injury caused by soil-applied herbicides. Environment-induced crop stress, often caused by cool, wet soil conditions, can enhance soybean injury from soil-applied herbicides. In most cases, herbicide selectivity arises from the soybean plant’s ability to rapidly metabolize the herbicide to a nonphytotoxic form before it causes much visible injury. Soybean plants growing under favorable conditions are able to adequately metabolize the herbicide before any injury symptoms are expressed. However, when the soybean plant is under stress, its ability to metabolize the herbicide can be sufficiently reduced to the point at which injury symptoms develop.
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