Growers should take a big picture approach to herbicide applications this autumn to get maximum control while protecting the chemical toolbox for the future.
Corteva Agriscience, the agriculture division of DowDuPont, says a residual followed by a contact herbicide in the autumn or spring has consistently proven to be the most effective strategy to controlling key problem weeds in winter cereals.
However, a significant amount of growers are still opting to skip residual treatments, or not applying a sufficient quantity to achieve optimum results.
Ryegrass and brome are key targets for the approach but the advice is equally applicable to broad-leaved weeds.
Dr Alex Nichols, cereal herbicide product manager, said Corteva’s Crystal (pendimethalin + flufenacet) applied at pre or peri-emergence of winter wheat followed by Broadway Star is shown to take out 99% of sterile brome.
Dr Nichols said: “Similar results have been obtained for ryegrass control with the use of Defy (prosulfocarb) as a residual herbicide followed by Broadway Star.
“The reason we see better results when used in a programme is because the residual either takes out or heavily restricts growth of some early-emerging grassweeds.
“When the contact herbicide is applied, often in the spring, it is dealing with smaller weeds.
“Trying to control a sterile brome plant that germinated with the crop or soon afterwards would leave a plant that is far too big to be controlled effectively by a selective herbicide.”
The use of a programme is also key to reducing the risk of resistance developing.
Growers are using different modes of action while significantly reducing seed return, Dr Nichols explained.
Despite the compelling case market data shows a significant number of growers are not using a residual.
“Of the 250,000ha which get a treatment of Broadway Star, 10% is not preceded by a residual and as much as 40% is not getting sufficient residual,” Dr Nichols added.
It’s not only grassweeds that need consideration; broad-leaved weed control in winter cereals can benefit from a programme with residual herbicides.
“Relying on spring applied contact broad-leaved herbicides alone is a recipe for problems – weeds will be either too big for effective control and the probability of resistance developing will be high,” Dr Nichols said.
In situations where ALS resistant poppy is present, using Stomp Aqua (pendimethalin) in the autumn is one solution to controlling large flushes of weeds that follow drilling.
This can then be followed by application of Zypar (Arylex Active) in the spring, targeting weeds at the four-to-six leaf stage.