Ontario Grain Farmer March 2023

Glyphosate, 540 grams/litre applied at a rate of 1.34 litre/acre, resulted in those potted sow thistles producing close to zero shoots and root growth. Similar results occurred with Enlist 1 (720 millilitres/acre) at the highest label rate. Among others tested, Engenia (dicamba) at a rate of 0.4 litre/acre produced good root and shoot control but not as good as glyphosate or Enlist 1. OTHER CONTROL METHODS Because sow thistle has dormant roots in the fall, fall-seeded cover crops will have little impact, but those present in the spring can help reduce sow thistle shoot biomass. 14 Moldboard plow tillage is the best nonchemical treatment, says Cowbrough, and best done in the spring. Deeper plowing of 25 centimetres is preferable, using a disc harrow. "This is what it takes for meaningful sow thistle control," he explains. To those farmers reluctant to do that, he suggests that "if you are really struggling with sow thistle control, you have dense populations, try it on a small scale and then scale it up if it's working." A Weed Zapper can be used to flame the plants in the spring, which at the very least stops seed production, but there has not been much study into how this method impacts root growth. BLUEGRASS Cowbrough and his colleagues identified five species of bluegrass in 2021 and 2022 in the counties of Bruce, Essex, Haldimand, Middlesex, Waterloo, and Wellington. Fifty per cent of samples were annual bluegrass, with the remainder being perennial species: roughstalk bluegrass, fowl meadow grass, Canada bluegrass, and Kentucky bluegrass. "At this point, I'm not sure how important it is to be able to differentiate between the BLUEGRASS. PHOTO COURTESY OF MIKE COWBROUGH. continued from page 13

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