When it comes to spraying crops in preparation for harvest, producers need to decide whether they want to target dry-down or weed control.
"A pre-harvest application of glyphosate will give you weed control, that's its main objective, but it also can result in some crop dry-down, though it tends to take a quite bit longer," says provincial weed specialist Jeanette Gaultier. "Whereas when we use a true desiccant... they're contact products, so they're basically working to dry-down the crop material, and while they will provide weed control for the green weeds in the field, they're only burning off that top growth."
Gaultier says it's important to understand the difference because of the way the chemicals work. She explains a desiccant is a contact product, meaning it doesn't move within the plants. So even if applied at the incorrect time, desiccants don't typically cause issues with maximum residue levels (MRLs). On the other hand, she explains glyphosate is a systemic product, which means it will move to the growing point or grain at harvest time.
"If (glyphosate) is applied too early, then we can definitely see an accumulation (in the grain)," Gaultier says. "The other problem on the opposite end, if we do apply a contact product and harvest before the pre-harvest interval, there is a chance that product can still be on the grain and not have broken down from the application."
In addition to pre-harvest intervals and maximum residue levels, Gaultier says it's important to consider how the product is applied.
Source : Portageonline