One of the reasons weed species can be so difficult to get ahead of is because of their ability to adapt to conditions.
Herbicide labels often refer to weed size when targeting the ideal control window, but in dry conditions weeds can stay small while rapidly move towards maturity.
Mike Cowbrough, weed specialist for the Ontario Ministry of Agriculture, Food and Rural Affairs, warns that assuming small weeds will be easy to control could leave farmers disappointed with the level of control achieved if they delay a herbicide pass.
That’s because under dry or drought conditions, weeds begin to mount whatever drought protection they can, including building up waxy layers or adding hair. They also rush development, says Tammy Jones, technical sales agronomist with Corteva AgriScience, and can reach maturity even at a very small size. Kochia, she says, can be one of these plants that becomes incredibly difficult to kill in a drought scenario.
The bottom line is dry conditions can create a false sense of security for weed control. Cowbrough says it’s even more important to scout fields carefully and stage weeds not just on size but on maturity, too. A more developed weed is harder to kill or could be much closer to setting seed than you realize.