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Weed Management

Bayer Crop Science

Practical benefits of mixing modes of action

Article overview

- Background of MoA trials

- Trial results

- Comparison with product trials

- Practical steps

Background of MoA trials

There are currently actives from six HRAC Mode of Action (MoA) Groups that farmers can use at pre-em and early post-em against black-grass and Italian ryegrass. A seventh, bixlozone from HRAC Group 13 is due in the near future, there is also glyphosate and post-em chemistry for other points in the programme.

Over the last decade, weed control has shifted to the pre-em timing often with a high loading of flufenacet used to improve control. But with a greater choice of actives now available, farmers should look to diversify MoA rather than increase the loading of one or two actives.

“We were interested in investigating the benefit of adding more MoA versus simply applying a higher total dose of herbicide,” says John Cussans. “Many trials done by manufacturers and distributors tend to look at products at full rate, which is how farmers use them and what we generally recommend for resistance management.”

“But such trials don’t really tell you if you get better control because you have diverse MoA, or the effect is from just applying more herbicide in total. We wanted to investigate this.”

NIAB set up a matrix trial with five pre-em MoA in total and the highest total loading was equivalent to five label rates of herbicide. Hence, at the lowest total dose, the trial compared the efficacy of one active applied at label rate compared to five actives in a stack at 1/5 of the label rate for each active. At the highest rate, a 5-times label rate of flufenacet (1200g/ha) was compared to five different actives all at the label rate.

Number of MoA

Total dose – label rate





1 x label rate

3 x label rate

5 x label rate


0.33 x label rate

1 x label rate

1.67 x label rate


0.2 x label rate

0.6 x label rate

1 x label rate

The trial set up is different to the standard herbicide trial and includes application rates – high and low – that aren’t recommended for use on farm, but it does show how both factors of total dose and mode of action diversity affect control.

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