Greenhouse experiments were conducted to determine whether multiple applications of glyphosate and time of glyphosate application with regard to the crop's growth stage had a significant effect on the growth and development of glyphosate-resistant canola. Glyphosate was applied as single applications at the two-, four-, or six-leaf stage of canola; as sequential double applications at the two- and four-, two- and six-, and four- and six-leaf stages of canola; and as a triple application at all three stages. Of the plant growth parameters measured, single applications of glyphosate resulted in significant reductions to stem weight and shoot weight compared with nontreated plants, and multiple applications of glyphosate caused significant reductions to leaf area, leaf weight, stem weight, and shoot weight. Single applications of glyphosate were less injurious to glyphosate-resistant canola compared with multiple applications, and canola growth parameter reductions were greatest after earlier glyphosate applications.

Nomenclature: Glyphosate, canola, Brassica napus L.

Additional index words: Crop injury, herbicide-resistant crop, leaf stage, multiple application.

Abbreviations: EPSPS, 5-enolpyruvylshikimate-3-phosphate synthase; RH, relative humidity.