Ontario Grain Farmer March 2021

10 THE 2020 GROWING season saw many reports of crop injury due to herbicide carryover. Some crops grown in Ontario are very sensitive to carryover, particularly some horticulture crops. When growing crops on land that could have a sensitive crop planted after, it is important to pay attention to what herbicides are being applied. “Prevention is the most critical piece of preventing crop injury due to herbicide carryover,” says Dr. Darren Robinson, University of Guelph Ridgetown Campus. Robinson presented the Herbicide Carryover session at the Ontario Agricultural Conference along with Mike Cowbrough, weed management specialist at the Ontario Ministry of Agriculture, Food and Rural Affairs. The best way to prevent herbicide carryover is to know the crop rotation ahead of time, and ideally have the rotation planned at least four years ahead of planting. Robinson understands, “it’s a big ask. But by doing so farmers can better plan around known weed issues and which herbicides they can use that will be compatible”. When working with vegetable crops, there are many of them that it is imperative to Herbicide carryover PREVENTING CROP INJURY Laura Ferrier HERBICIDE CARRYOVER IN OATS AND FALL RYE. PHOTO COURTESY OF DR. DARREN ROBINSON. watch for herbicide carryover. There has been reports of carryover injury in sugar beets up to three years, as they are very sensitive. For the field crops side, there is a little less to worry about. Although it was noted that edible beans can show some herbicide injury, with each type of edible bean responding differently. Robinson says that once the crop rotation is established, farmers should have good soil mapping done and know their soil characteristics including texture, organic matter, pH, and cation exchange capacity as they all have an impact on herbicide persistence in soil. A composite sample would be the bare minimum, ideally grid sampling would be the best option. READ LABELS It is imperative to read labels, paying close attention to what the rotation restrictions or re-cropping guidelines are. Being sure to reference the correct region of Canada when looking at labels, as restrictions can change across the country. Re-cropping restrictions can also be found in Publication 75, Guide to Weed Control. Re-cropping restrictions are established by two- to three-year trials being completed. Each herbicide company needs to produce the results on their label. Every trial includes sugar beets, due to their sensitivity, along with several different potentially sensitive crops from different crop groups. Twice the labelled rate is typically used to simulate overlap, and to give some conservative results or to take into account if there are extreme weather events, essentially creating a worst-case scenario. For each trial, visual crop injury, biomass, multiple stand counts at set intervals, along with stand counts after a heavy rainfall event, are collected along with yield. The determined re-cropping interval is typically based on yield and crop injury for most crops. Agronomy TILLAGE NO TILLAGE