‘Spray herbicide early to control grass weeds’

Winter cereals are currently being planted where weather allows. Once sowing is completed, farmers should start looking at their autumn herbicide options.

As IPU (isoproturon) goes off the shelf of the chemical store – it can’t be used after September 30 – tillage farmers face a new challenge on how to control grass weeds.

Grass weeds, such as annual meadow grass, are a problem in Ireland – especially in winter cereals.

IPU was a cost-effective and flexible product as regards timing. Despite its exit from the market, there are plenty of options available for good control of grass weeds.

The main message coming from advisors is that early application is essential for good control – particularly for annual meadow grass.

Teagasc’s Ciaran Collins said: “Pre-emergence spraying of weeds is the main message we want to get across to farmers.

Control of grass weeds in winter barley works best pre-emergence or – if it’s post-emergence – at the two-to-three leaf stage.

The Teagasc crops specialist also told farmers to avoid spraying when the plant is just peeping through the soil – the peri-emergence stage.

This can sometimes cause a discolouring of the crop and, while it’s not shown to have any effect on yield, it’s not nice to look at.

Collins added that integrated pest management (IPM) is extremely important.

Good ploughing, early chemical control, a competitive crop and delayed sowing can all help to control annual meadow grass.

The first thing that farmers should look at when deciding on what herbicides to apply is field history. Where grass weeds are a problem, a pre-emergence application should be used.

In instances where a pre-emergence herbicide is applied, the use of Redigo Deter dressed seed can save farmers a pass with the sprayer.

Options available

Pendimethalin has good control of grass and broad-leaved weeds and people will be most familiar with it in Stomp Aqua.

Flufenacet, chlorotoluron and picolinafen are all good grass control options as well. DFF should be included in all mixtures as part of a product or on its own for the control of broad-leaved weeds.

Some of the newer options to the market look like good alternatives. Vigon, a similar product to the reliable Firebird, also includes flurtamone. This helps to control both grass and broad-leaved weeds.

Tower, which contains pendimethalin and DFF, also includes chlorotoluron. Chlorotoluron is part of the same chemical group as IPU, which is good on both grass and broad-leaved weeds.

Pontos offers good control of annual meadow grass and it can be mixed with pendimethalin.

Where sterile brome is an issue, a pre-emergence spray is essential in both wheat and barley.

Brome can be a serious problem in winter barley. Farmers should consider an alternative crop as there are more control options available.

If this is not possible, full rates or two application timings may be used where the label allows. Broadway Star is a good post-emergence option; but on wheat only.

If cleavers and troublesome broad-leaved weeds, such as fumitory and poppy, are an issue in winter wheat, Allister Flex is an option. It contains two sulphonylureas (SU) that can only be applied post-emergence.

Teagasc examples:
  • Firebird 0.3L/ha (winter barley and winter wheat);
  • Flight 4.0L/ha (winter barley and winter wheat);
  • Defy 2.0L/ha and DFF 0.1L/ha (winter barley and winter wheat);
  • Tower 2.0L/ha (winter barley and winter wheat);
  • Vigon 0.5L/ha (winter barley) 1.0L/ha (winter wheat);
  • Pontus 0.5L/ha and Flight 3.5L/ha (winter barley and winter wheat);
  • Allister Flex 1.0L/ha (winter wheat).

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