Better Farming |January 2025

41 The Business of Ontario Agriculture Better Farming | January 2025 I remember the first field of Group 2-resistant foxtail I saw. It was a purple-green. As soon as I saw it, I knew what was happening. There were no other weeds except this foxtail. Jump ahead to the late 1990s. We were introduced to Roundup-resistant soybeans. I remember someone jokingly saying that once the crop emerged, we should fill the sprayer up on Monday and spray all week with Roundup. Next Monday do it again. Do this until the crop canopies. Guess what we got? Glyphosate-resistant weeds. We were assured that weeds could not become resistant to glyphosate. Wrong! So that is the short “resistant” story. And we must remember this story as new genetically herbicide-resistant crops are developed. Overuse of any herbicide will develop resistance. If you had great results with either the Xtend soybeans or Enlist E3 soybeans, consider switching after two or three years to the other system. I don’t think you should use both systems the same year, especially if you are planting soybeans after soybeans. I’m excited about Bayer’s new soybean varieties, HT4 Fourth-Gen Phase 3. They hope to introduce these in 2027. These varieties are resistant to glyphosate, certain formulations of dicamba, glufosinate (Liberty), mesotrione (Callisto), and certain formulations of 2,4-D. This should help a lot with the new weeds that have cropped up in the last few years. But looking further, I conclude that most of the new weeds are coming from soybean fields, the glyphosate resistance is because of repeated use of glyphosate, and the really bad new resistant weeds are coming from the United States. They have huge expanses of soybeans that are sprayed with glyphosate. I also believe that bigger fields and large tracts of contiguous acres of soybeans all being sprayed with the same herbicide increases the probability of more resistant weeds and cross pollination to develop resistant weeds. I do not subscribe to the theory that the resistant weeds were always in the population. I believe they came from random cross pollination. When you have large areas of fields sprayed with the same herbicide, you increase the probability of random cross pollination. I can’t get any weed scientist to agree with this theory, though. When I look back on historical weed control in Ontario, farmers regularly switched herbicides. We used a lot of different groups, such as Treflan (Group 3), atrazine (Group 5), and Eptam (Group 15), but the big thing is that while many of these herbicides were in the same group, they controlled different weeds. The Group 5 herbicides included atrazine, Bladex (cyanazine), linuron (Lorox), metribuzin (Sencor) and even simazine. Atrazine at high rates controlled many perennial weeds like perennial sow thistle, bindweed, and quackgrass, but Bladex at high rates did nothing to control these weeds. The restricted use of different active ingredients has led to more weed problems. Certainly, the reduced use of the triazines (both atrazine and metribuzin) allows more weeds to establish later in the season. Chickweed comes to mind. Current herbicide programs do not address chickweed seedlings. When we used atrazine, it controlled those late flushes of weeds. Certainly, dandelion seedlings become established in corn fields where no residual herbicide is used. When we used high rates of atrazine and two years corn, there were fewer problems with perennial sow thistle and dandelions. Something I relied on a lot this year was the Crop Protection Hub under the control of OMAFA (formerly OMAFRA). The weed control section is overseen by Mike Cowbrough, provincial weed specialist. In this program, you pick a crop, spray timing, and weed to be controlled. Pretty simple to use. For 2025 Mike hopes to add a function that lets you compare weed control of various treatments and then print that off somewhat similar to the format that was in the old Publication 75. Mike is a very hardworking professional, positive, and in tune with current weed problems. This year, he did work on how to control burdock. In no-till and pasture fields, burdock creeps in and becomes a problem. crops: the lynch fileS

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