"Shoot growth will continue until what's called the basal rosette (five leaf) reaches the 'compensation point,'" he says. "This is when the carbohydrate reserves change course and go from shoots to roots… If herbicides are applied at this stage, it means you're less likely to get re-growth, and if the herbicides are systemic, they will move down into the roots." Herbicides should be applied in corn at the V1 to V6 stage, and in soybeans, from the first to third trifoliate. HERBICIDE STUDY Cowbrough has conducted an experiment of sow thistle control with the weeds planted in pots. He chose a few systemic herbicides deemed most effective based on the scientific literature and anecdotal reports from around the province. He measured shoot growth and found a range of responses. "I quantified the root mass as well because I was interested to see if herbicides, especially the systemic ones, had any impact on reducing ONTARIO GRAIN FARMER 13 MARCH 2023 continued on page 14 Reducing [sow thistle] shoot growth is best done in the spring through herbicide use, flaming or cutting, and the key is repetition – stopping re-growth is absolutely critical. root growth as well as shoot growth," he says. "As expected with sow thistle, it was pretty amazing in terms of the level of root mass. One two-inch root fragment produced 46 grams within eight weeks, three times the amount of biomass than what's produced in the shoot, so that's almost a three-toone ratio." When recycling ag containers, every one counts Great job recycling empty pesticide and fertilizer containers (jugs, drums and totes). Every one you recycle counts toward a more sustainable environment in your agricultural community. Thank you. Ask your ag retailer for an ag collection bag, fill it with rinsed, empty jugs and return to a collection site. REMEMBER! You can also return empty seed, pesticide and inoculant bags for environmentally safe management. Details at cleanfarms.ca Find a collection location near you at cleanfarms.ca info@cleanfarms.ca @cleanfarms
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