Staging wheat for pre-harvest weed control can be tricky, especially in years when the crop is uneven due to poor conditions. Pre-harvest staging is critical to avoid any herbicide residues in the grain, which can lead to Maximum Residue Limit (MRL) and marketability issues. A wheat plant is considered physiologically mature at 30% moisture; this means grain fill has stopped, and final yield and kernel weight/size have been determined. Spraying pre-harvest products such as glyphosate, before 30% grain moisture, can negatively impact grain quality and marketability. Research has shown that the application of glyphosate at the soft dough stage (GS 71-85 with >30% moisture) had negative impacts on kernel weight, protein content, and end-use quality (Malalgoda et al., 2020). The application of glyphosate before the hard dough stage – can halt the physiological plant maturity, disrupt grain fill and lead to decreased yield and quality. It can also result in unacceptable residues in harvested grain, causing market acceptance issues.
MAXIMUM RESIDUE LIMITS
MRLs represent the maximum amount of a pesticide that can be expected to remain on a food product (such as wheat) when the product is used according to label specifications. MRLs are not a representation of food safety; they are mainly used for trade purposes to ensure Canadian crops meet MRLs set by export countries.
PRE-HARVEST INTERVALS (PHIs)