EFFICACY AND ECONOMICS OF HERBICIDES FOR CANADA THISTLE (CIRSIUM-ARVENSE) CONTROL IN NO-TILL SPRING WHEAT (TRITICUM-AESTIVUM)

The objective of this field research was to compare relative effectiveness and profitability of alternative herbicides applied to the same plots for four consecutive years for controlling and reducing dense Canada thistle infestations in no-till spring wheat. Chlorsulfuron at 30 g ai ha-1 plus nonionic surfactant or clopyralid plus 2,4-D at 70 plus 280 g ae ha-1, respectively, applied annually for 4 yr controlled Canada thistle and was more effective for gradually reducing Canada thistle stands than 2,4-D at 560 g ae ha-1, MCPA plus bromoxynil at 280 plus 280 g ae ha-1, or tribenuron at 20 g ai ha-1. Chlorsulfuron and clopyralid plus 2,4-D also controlled Canada thistle greater-than-or-equal-to 90% earlier (by 2 yr) than other treatments. Stochastic dominance analysis, a form of economic analysis, predicted that either chlorsulfuron or clopyralid plus 2,4-D would be preferred by farmers to the untreated check, MCPA plus bromoxynil, or 2,4-D treatments. Chlorsulfuron also would be preferred to clopyralid plus 2,4-D by risk-neutral farmers, whereas clopyralid plus 2,4-D would be preferred to chlorsulfuron by highly risk-averse farmers, those who are most likely to pick only consistently effective herbicides.