Controling Weeds in New Grass Leys

Clover or non-clover, weed control is more readily achievable when weeds are seedlings, say Teagasc researchers.
calendar icon 17 September 2013
clock icon 2 minute read

Control of weeds like docks, thistles and fat-hen is most cost-effective when grass leys are new. What herbicide you choose depends on clover in the ley. 

What weeds do I need to worry about?

Annual weeds such as Fumitory, Fat Hen, and Deadnettle only live for 1 year. These weeds should not affect the establishment of the new sward (unless present in high numbers – if so spray them). They are normally removed by grazing, cutting or leaving them die naturally over winter.

Perennial Weeds such as Docks, Dandelions, Creeping Buttercup, and Creeping Thistle etc can be tolerated (at low numbers) in an intensive grazing situation, however it is still better to spray them now rather then in a few years time. In silage/hay fields you should always spray for weeds after re seeding as they will build up their root reserves and take over the grass.

Help the spray work

  • Have an even, vigorously growing sward.
  • Apply the herbicide onto small, actively growing weeds (e.g. dock leaf = size of €2 coin)
  • Spray 6-8 weeks after re-seeding when there are 3 leaves on the grass and I true leaf on the clover
  • Avoid spraying in very dry or cold conditions (talk to your advisor/merchant if this is the case).
  • Keep water rates high 220-350 l/ha (20-30 gallons per acre).
  • Remember to keep the prescribed cross-compliance records and follow the product label.

  • Field re-seeded late Autumn 2009
  • Re-seed herbicides applied Spring 2010
  • Medium to high dock populations with little or no developed tap root
  • Very good control of docks for 3 years from a re-seed spray
  • Can introduce clover (over-seeding method) after using non-clover safe (e.g. Dockstar) sprays.

Teagas Herbicide Sheet for New Leys

Teagasc Susceptibility Guide to Herbicides in New Leys

New Seeds? 

Do I need to spray my new ‘clean’ re-seed?

  • Yes (in most cases) as there is up to 100,000 dock seeds per acre ready to germinate in fields.
  • Yes as you will kill all weeds easier when they are seedlings
  • Yes as you will maximise your investment

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