Ontario Grain Farmer - September 2021

“If a tank mix is applied, you must use the longest pre-harvest interval of the products used,” cautions Bob Thirlwall, market development agronomist for Bayer Crop Science. He also advises farmers against pre-harvest herbicide applications in Identity Preserved (IP) and other non-GMO varieties since contracts from some buyers prohibit the practice. Where pre-harvest herbicides are permitted, however, farmers need to apply substantially more liquid per acre to achieve adequate coverage on weeds which frequently reach two or three feet in height. Thirlwall recommends a per acre rate of 15 gallons as a guideline. “Coverage is really important,” he says. “I think most people realize that, but its probably one of the most important things.” TIMING The timing has to be right as well. Dry conditions and the resulting partially hardened-off weeds can be slow to show herbicide response, so an earlier application might be required. Particularly with IP varieties, however, Thirlwall reiterates it is critical to not spray before maturity is near — specifically when moisture levels are at least 30 per cent or lower. Cowbrough and Bohner similarly say applying herbicides too early can result in yield losses and chemical residues within soybean seeds, the latter being a serious problem at marketing. Waiting until seed fill is complete is the best option. Seed fill, they say, can be determined by “a colour change of the seed from green to yellow…A change in colour is defined by the absence of any green colour left on the pod. At least 90 per cent of the pods need to have changed colour and no longer contain any green. This stage of the crop typically occurs when there is at least 80 per cent leaf drop, although a field should not be assessed by leaf drop alone.” Seeds separating from the white membrane within the pod can also indicate spray readiness. Analyzing randomly selected pods from the top third of different plants — maturity is generally more advanced on lower parts — is a good way to check. Cowbrough and Bohner provide a full list of pre-harvest herbicides for use in soybeans in their article “Pre-Harvest Herbicide Timing in Soybeans” available at fieldcropnews.com . Always read and follow the label for directions on use and precautions of all herbicides. l ONTARIO GRAIN FARMER 23 SEPTEMBER 2021 Using the right product for the weeds present, and spraying at the right time, is critical. services services CONTACT US FOR A FREE ENERGY CONSULTATION! (866) 818-8828 sales@agenergy.coop agenergy.coop BEANS HAVE SEPARATED FROM POD. PHOTO COURTESY OF MIKE COWBROUGH.