Crop Group #4 herbicide screening trial

Project Code SCR07-001

Project Lead

Rob Grohs - University of Guelph


To evaluate reduced-risk herbicides for potential to control broadleaf weeds in several leafy vegetable crops, and to provide recommendations for reduced-risk candidate herbicides to be pursued for registration in Canada

Summary of Results

Leafy vegetables (specifically spinach, Swiss chard, arugula and lettuce) are significant crops for horticultural producers in Ontario and Quebec, but the lack of weed control products means that growers spend considerable effort and money to control weeds. Many of the products used to control weeds in other crops cannot be used with leafy vegetables due to their sensitivity to the herbicides and the unacceptable levels of crop injury that would result.

The objectives of this project were to test 10 reduced-risk herbicides for their efficacy in suppressing broadleaf weeds in spinach, Swiss chard, arugula and lettuce crops and to evaluate the phytotoxic effects of these products on the four species of leafy vegetables.

Field trials were conducted in 2007 at the Simcoe Research Station of the University of Guelph, in Ontario. The experimental design was a randomized complete block design with four replications. Plots were 4 m by 1.8 m. The 10 herbicides evaluated were applied at three rates: 0.5×, 1× and 2×. Herbicide treatments were either pre-emergence or post-emergence to the weeds. Data were collected on the rate of injury to the leafy vegetables and the degree of efficacy in controlling four broadleaf weeds, specifically Amaranthus retroflexus, Chenopodium album, Solanum ptychanthum and Protuleca oleraqcea.

Most of the herbicides tested were found to be effective in controlling the four species of weeds. However, all of the herbicides tested caused injury to the four species of leafy vegetables. The highest degree of crop injury was in lettuce.

Given the injury to the leafy vegetables, none of the pesticides tested can be recommended for use in these crops. However, further studies will be carried out using the pesticides that caused the least injury to the leafy vegetables. Repeated applications of these herbicides at very low rates will be tested, since this technique has already been used in other crops to eliminate young weeds as they emerge from the soil.

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