46 Better Farming | September 2024 Follow us on @BetterFarmingON crops: the lynch fileS WEED CONTROL IN SEPTEMBER & OCTOBER Killing weeds in the fall gives you more time in the spring. By Patrick Lynch I’m going to share another discussion I had with farm supply retail dealers at an industry breakfast meeting this past spring. Me: “So, how is your spring going?” Dealers: “Not too bad, but we have a lot of herbicides to get on and in some fields. The weeds are getting big. Not sure if we can control the big ones like big Canada fleabane and dandelion.” Me: “So, what is the solution?” Dealers: “We have to get more people controlling weeds in the fall. The biggest problem is weeds are too big now. We can’t get to all the acres on time.” I knew this discussion was occurring all across Ontario, not just at our meeting. And this is not the first spring where we had a weed problem; we go through the same thing for most springs. In the spring of 2017, there were many days when it was too cold to spray, but growers wanted to spray fungicides and herbicides on wheat. We could’ve sprayed the fungicide, but the weather was too cold to allow us to spray herbicides. Some growers sprayed anyway and burnt the crops. Other growers made two trips. The obvious solution is to control weeds in wheat in the fall. I realize last fall was too wet for some growers to even think about fall weed control. The focus was on trying to get beans off between rains. But some of you were able to control weeds last September and October either as pre-harvest, post-harvest, or in winter wheat. So, what are the possibilities? You can control weeds after harvest of cereals, corn, or soybeans. A high-speed disc will not control perennial weeds, though. Weeds like dandelion and chickweed are just moved around. Other weeds like perennial sow thistle are cut up and spread around. They are not killed. In fact, a high-speed disc can make perennial sow thistle worse. A high-speed disc will control annual weeds that will die anyway, but it will not control big winter annuals and certainly not perennials. If you want to control perennial weeds like dandelion, wild carrot, or burdock with tillage, the only tillage tool that will work is a moldboard plow, and the weeds must be completely buried. For most farmers, moldboard plowing is not an option. This means you depend on herbicides. And not just any herbicide. You have to know what weeds you have and then pick the appropriate herbicide. Using glyphosate and hoping the weeds will die is not an option. Mike Cowbrough, with the Ontario Ministry of Agriculture, Food and Agribusiness (formerly OMAFRA), has put together a great weed control program available at cropprotectionhub.omafra.gov.on.ca. This program, the Ontario Crop Protection Hub, allows you to put in your crop, weed problem, and control at different timings. You are given different herbicide treatments and the control percentage you can expect with each treatment. You should know if your weed is resistant to any herbicide. For instance, glyphosate is listed as a herbicide to control Canada fleabane but most fields have glyphosate-resistant fleabane. Timing of fall herbicides is an issue. Purdue University researchers suggest that weeds are either cold-sensitive or cold-tolerant. Cold-sensitive weeds do not readily take up herbicides after a light frost. Weeds in this group include dogbane (looks a bit like milkweed), milkweed, and bindweed. Spray these before a frost. Pre-harvest weed control in soybeans is an option. Patrick Lynch photo
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