Determining Exposure to Auxin-Like Herbicides. I. Quantifying Injury to Cotton and Soybean

Abstract

Crop injury caused by drift of auxin-like herbicides has been a concern since their development. Research was conducted to describe a method of quantifying injury from auxin-like herbicides as a first step in determining crop damage. Reduced rates of 2,4-D, dicamba, and triclopyr were applied to cotton and soybean plants in the three- to six-leaf stage in field and greenhouse studies. Injury to leaves and stems were evaluated separately, and the values were combined so that one injury estimate was obtained for each individual plant rated. Injury symptoms were typical for auxin-type herbicides and ranged from slight bending of stems or petioles and wrinkled leaves to necrosis. Specific descriptions of leaf and stem injury levels were used to describe plant injury consistently. These descriptions were very detailed for the lower injury levels, but the characterizations became more general as the injury increased because of the prominence of factors such as necrosis. The injury evaluation method provided repeatable results for each herbicide and herbicide rate used. This injury evaluation method has many possible uses in auxin-like herbicide research and lays the foundation for forecasting the impact of early-season injury to cotton and soybean yield.