By: Mitchell Japp, PAg, Provincial Specialist, Cereal Crops
Pre-harvest glyphosate gets a lot of interest at this time of year. However, some of the discussion is misleading. So, to be clear, glyphosate is not a desiccant.
Glyphosate offers options for pre-harvest perennial weed control in wheat barley and oats, as well as other crop types. However, crop staging is critical to ensure that glyphosate residues do not accumulate in the grain.
Crop staging for glyphosate application is at the end of hard dough stage, or when grain moisture content is less 30 per cent. At the end of hard dough, a thumbnail pressed into the kernel will leave an indent. The colour of the field is not an indicator of kernel ripeness.
Glyphosate application should be at least seven days prior to harvest to allow time for the herbicide to work.
At the end of hard dough stage, the crop has reached physiological maturity, so the seed is at its maximum dry weight and no longer receives food from the plant. Glyphosate applied after this stage, therefore, will not translocate from the plant into the seed.
It is important that the entire area sprayed meet these minimum requirements for application. This includes later tillers and areas that have matured more slowly. Grain from later tillers or greener areas of the field could accumulate glyphosate if applied too early. In addition to creating a marketing risk, yield can be reduced and kernels can be shrunken, potentially reducing test weight.
Glyphosate is of increasing interest in some export markets. Countries set Maximum Residue Limits (MRLs) for crop protection products in grain and may go so far as to reject the shipment if it exceeds those limits. It is important to preserve export markets by following the label for the use of pre-harvest products like glyphosate, as well as any other crop protection product.
Malt barley growers are already familiar with zero tolerance on the use of pre-harvest glyphosate. Oat growers are becoming more familiar with limitations on glyphosate since one miller found issues with oats treated with glyphosate. Pre-harvest glyphosate is a tool for perennial weed control, but it is a tool that needs to be used wisely to ensure it can be used in the long term.
Cereals Canada, along with the Canadian International Grains Institute (CIGI) and the Canadian Grain Commission, has been promoting Canadian wheat to international customers through trade missions over the past two winters. From their discussions with buyers, they have recognized glyphosate is a concern and that it is important to keep glyphosate levels as low as possible. At home, Cereals Canada has developed a Keep it Clean campaign, based on the same campaign for canola. This information is designed for growers to help ensure that buyers of Canadian wheat keep coming back for more.
Basically, it just comes down to checking and then following the label.