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Agronomy update: Top tips on weed control

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Newly planted crops

Planting is drawing to a close and early planted crops are now beginning to emerge. As Miscanthus is very susceptible to weed competition in the first 2 years after planting it is important to plan and apply pre-emergence herbicides before the crop emerges. This is especially important where grassweeds are present in the field and/or where no glyphosate was used pre-planting. Emerging weeds should be dealt with using an application of glyphosate. Also the inclusion of pendamethalin will give a good start to broad leaved weed control.

Miscanthus amongst blackgrass

Transplanted blackgrass surrounded by newly emerged blackgrass at 1-2 leaves. Glyphosate wasn’t used pre-planting.

Currently there are only 3 commercially available glyphosate products approved for use on Miscanthus between planting and emergence. These are off-label approvals under an Extension of Authorisation for Minor use (EAMU):

Product MAPP Manufacturer Active Max Rate EAMU #
Roundup Energy 12945 Monsanto glyphosate 3.2 l/ha 2888/2008
Roundup Flex 15541 Monsanto glyphosate 3.0 l/ha 2131/2013
Roundup PowerMax 16373 Monsanto glyphosate 1.89 kg/ha 1300/2014

Currently there are only 4 pendamethalin products approved for use on Miscanthus under an Extension of Authorisation for Minor use (EAMU):

Product MAPP Manufacturer Active Max Rate EAMU #
Aquarius 14712 Adama pendamethalin 3.3 l/ha 3298/2009
Cinder 14526 Adama pendamethalin 3.3 l/ha 2208/2009
Stomp 400 SC 13405 BASF pendamethalin 3.3 l/ha 2923/2008
Stomp Aqua 14664 BASF pendamethalin 3.3 l/ha 2919/2009

Before applying any pre-emergence herbicides to the crop please take time to look for any emerging stems. Be careful as just a few emerged stems in small area can represent a significant percentage emergence. If in doubt, leave it out!

Newly Emerging Miscanthus Stems

Newly emerging stems

Where the timing for pre-emergence grassweed control with glyphosate has been missed, there are currently no post-emergence herbicide options. It is therefore important that pre-emergence glyphosate with a residual partner is used the following season to tidy up.

Established Crops

As stems start to emerge now might be a good time to assess existing crops. Of interest would be areas of perennial weeds or areas where plant density is low. Could the weeds be reducing yield? Could areas of low plant density be patched planted to improve crop performance? Are soil indices holding up? It’s generally recommended that fields are sampled once every 4 years and a basic soil analysis undertaken to assess ph, Phosphate (P), Potash (K) and Magnesium (Mg).


Only pesticides with a valid EAMU (Extension of Authorisation for Minor Use) can be legally used on Miscanthus crops. You must have a copy of the EAMU document before spraying as it forms part of the pesticide label. All conditions of the pesticide label and EAMU must be met. READ THE LABEL BEFORE USE. USING A PRODUCT IN A MANNER THAT IS INCONSISTENT WITH THE LABEL MAY BE AN OFFENCE. FOLLOW THE CODE OF PRACTICE FOR USING PLANT PROTECTION PRODUCTS. While every care is taken in the preparation of these agronomy notes, we cannot accept responsibility for unsatisfactory results.

If you have any queries please contact Russell Armstrong on 07535 649 111 or