Evaluation of Herbicides as Desiccants for Lentil (Lens culinaris Medik) Production

The indeterminate nature of lentil (Lens culinaris Medik), in conjunction with adverse field conditions, can lead to varying degrees of maturity among plants at harvest. This variable maturity may have a negative influence on lentil production and can delay harvest. Desiccants are currently used to improve lentil crop dry-down. However, applying desiccants too early may result in reduced crop yield and quality, and also leave unacceptable herbicide residues in lentil seeds. In addition, only four herbicides (glyphosate, diquat, saflufenacil, and glufosinate) are registered as desiccants for lentil desiccation in Canada, which limits options for growers. Therefore, the objectives of this thesis were i) to determine the importance of desiccant application timing in affecting crop yield and quality, as well as herbicide residues and ii) to determine whether additional desiccants applied alone or tank-mixed with glyphosate provide better crop desiccation. Field trials were conducted at Saskatoon and Scott, Saskatchewan, from 2012 to 2014. In the application timing trial, glyphosate or saflufenacil alone, or glyphosate+saflufenacil generally decreased seed yield, thousand seed weight, and crop dry-down, and increased herbicide residue levels at earlier application timings. For example, when applied at 60% seed moisture, saflufenacil reduced yield and thousand seed weight by 22% and 10%, respectively, and resulted in glyphosate and saflufenacil residues greater than 2.0 and 0.03 ppm, respectively. Although there were no reductions in yield and thousand seed weight when desiccants were applied at 50% or 40% seed moisture, glyphosate residue exceeded 2.0 ppm. Application of desiccants at 20 or 30% seed moisture content had no effect on yield, thousand seed weight, or herbicide residues. These results indicate that desiccant application timing is critical, and should not be made before 30% seed moisture. In a second study, glufosinate and diquat tank mixed with glyphosate were the most consistent desiccants and provided optimal crop dry-down without reducing yield and thousand seed weight, and effectively reduced glyphosate residue. The other herbicides tested (pyraflufen-ethyl and flumioxazin) were found to be poor options for growers as they had sub-optimal crop desiccation and did not affect glyphosate residue