How best to tackle arable grass weeds

Grass weed management should vary according to crop establishment system.

A flexible approach to grass weed management depending on crop establishment method can pay dividends, says a Suffolk grower.

Sam Slater operates a range of different establishment systems. These vary from no-till to plough – depending on the situation. Different establishment systems have a different impact on the weed profile, says Mr Slater.

“We have a meadow brome issue that has developed. I’m not convinced it is solely a no-till issue. I have analysed it quite a lot, and it’s certainly linked to min-till and a lack of ploughing. I also wonder if it is also partly due to our rotation.”

A double spring break crop can prove to be very effective in tackling meadow brome without resorting to ploughing, says Mr Slater, who farms at Stansfield, near Sudbury.

“We grow borage within our rotation, which has proved to be a decent break crop, especially because of its late drilling. Spring oats followed by borage has been particularly effective.”

Mr Slater is also getting extremely good brome control in winter beans. Later autumn planting allows for more opportunities to control brome pre-drilling and use Kerb (propyzamide) for control once the crop is established. 

Winter wheat tends to be drilled earlier in the autumn with the no-till system because of the limitations of disc direct drills in wet Hanslope series clay soils. He is also looking for a trash-free seedbed in this situation. 

Reducing risk

Although drilling earlier may increase the grass weed pressure, Mr Slater believes the no-till system compensates for this by reducing the risk of a dry spell impacting the efficacy of pre-emergence herbicides.

“Arguably, you can get better residual herbicide efficacy in a no-till situation going early because you haven’t got a drier cultivated seed bed, and the weeds are closer to the surface.

“If the land has been min-tilled, it dries out much quicker, which delays herbicide activation and degrades active ingredients. Although the same can happen in a no-till situation if there is a prolonged dry spell.”

Mr Slater does not believe it is a straightforward picture in the autumn because of the complexities of the interaction between soil moisture and blackgrass germination through the autumn. 

Herbicide strategies are the same across all establishment methods. They use a robust pre-emergence mix and plan to follow this with a further top-up. “We don’t really back off for one situation or the other.”

Because of his mixed grass weed population and meadow brome in particular, Mr Slater tends to include Avadex Factor (triallate) in his pre-emergence mix, saying the benefits of doing so are clear.

“Meadow brome is a concern for us, as well as black grass, and we are aware that there is more efficacy in triallate (against brome) than some of the other residual herbicide options. That has driven our choice.”

Practicality drives the choice between liquid or granular Avadex. Their land is spread out, they do not own an applicator and getting granules delivered at the right time and place for a contractor to apply is unfeasible.

“Choosing Avadex Factor is about logistics for us. We control the timing; it is going in our sprayer, so we control our pre-emergence herbicide application.”

Liquid or granular Avadex – which is best?

Farmer opinion is split over the merits of liquid Avadex Factor and granular formulation Avadex Excel. While Avadex Factor can be simply tank mixed with most other pre-emergence herbicides, the higher loading of triallate in Avadex Excel has led many farmers to opt for an additional granular application.

Reflecting on the performance in trials last season, Gowan technical lead Will Smith believes the performance of Avadex Factor and Avadex Excel is closer than many farmers may think.

“It is pleasing that both Avadex Factor and Avadex Excel are continuing to deliver a big benefit in weed control when used alongside other herbicide options as part of a grassweed control program,” says Mr Smith.

“We have picked up this season that Avadex Factor is performing extremely well  and, in some cases, even as well as Avadex Excel .”

“This is a trend we have noticed over the last few seasons, particularly when it has been wet at drilling. Our understanding is this is related to the formulation in these circumstances.”

Mr Smith says Avadex Excel still tends to deliver better control across a range of situations. Growers who have application equipment or a good local contractor who can deliver timely applications should continue to use it, he believes.

But farmers unable to apply granular products should have confidence that positive results for Avadex Factor means they can still improve their grass weed control by including liquid triallate in their herbicide programme.

Later drilling is where both products may sit alongside one another, adds Mr Smith.

It’s all very well drilling late, but programmes may look different in this situation, he explains.

“The weather may only allow one chance to get applications on. In this situation, Avadex Factor is a strong herbicide to be included in a tank mix.”