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Weed management advice for growers and agronomists

  • Blog
  • 3 min read

Employing an integrated weed management programme is crucial when establishing Miscanthus crops.

A heavy weed burden could knock a couple of tonnes off per hectare in yield in the early years, because they cause a smothering effect by competing for soil nutrients, water and sunlight.

Also, during the harvest season, weeds in bales are problematic for two reasons, the bale could be classed as contaminated as it’s not 100% Miscanthus or the green matter could add to the bales moisture content.

Tips for successful weed management:

Ploughing prior to planting, and flushing, combined with the fact that Miscanthus is planted in the spring can go a long way towards controlling blackgrass, and other common weeds.

But it’s vital that fields should be cleared of perennial weeds before any planting takes place. When you’re planting Miscanthus on ground that’s been down to long term pasture, remember to treat for wireworm first. Draw up a long-term weed control programme – remember that getting herbicide application right in the early days will play dividends as the crop takes off.

In the early months after planting, the farmer/agronomist should keep a regular eye on their crop. If they can walk it once a week or once every two weeks this is ideal. The earlier they can see weeds coming through, the quicker they can deal with them.

Having said all of this, generally you don’t want completely burn off the weed bed in the early months to the point of bare soil as a few weeds here and there can help the Miscanthus in the dry months as they insulate the land and actually reduce evapotranspiration – i.e. limiting the rate at which water is transferred from the land to the atmosphere by evaporation, and this helps Miscanthus because it thrives in moist conditions when establishing.

Common problematic weeds are black grass, woody brash, thistles, mayweed and redshank, but there are plenty more which can be very damaging to yields in the early months. Redshank and mayweed can create a blanketing effect as they grow very quickly and very densely, and blackgrass is always a big one to look out for, although it’s important to underline that the high canopy of the crop when its mature controls blackgrass.

With herbicides being lost to the market and some going off label at a relatively rapid rate, there can be confusion over how to treat a Miscanthus crop containing weeds. We’re able to update growers and agronomists on the Government’s HSE Pesticide EAMU’s, as the register can change every year and those who don’t abide by it can risk losing their Basic Payments.

At the moment, you can apply certain products containing the active ingredient glyphosate, after harvest to clean the seed bed, ideally spraying prior to the new buds emerging but if required, you can spray while the buds are a dark red colour, but must never spray when the buds start to turn green as they leaf out.

There are post-emergence treatments that you can apply, but many of these should not be sprayed or are ineffective after the Miscanthus is more than one meter in height or the weeds have passed specific leaf stages.

If in doubt, contact us at and we can answer your questions and queries on best practice for herbicide application, including when you can and can’t treat Miscanthus crops.