Getting to grips with the scourge of docks, thistles and rushes
Michael Keaveny looks at the control strategies for weeds which affect sward quality during the peak grazing season
DOCKS
A persistent problem on many farms, docks can seriously limit grassland output and productivity. Their seeds can remain viable for over 50 years in soil, have a large root system, and are very opportunistic in terms of where they germinate.
The best control for docks is good grassland management.
Maintaining a dense, leafy grass sward will smother out emerging docks. Having a fertile soil with adequate levels of N, P and K along with a suitable pH for grass growth is important. Avoiding poaching and overgrazing will limit the space for docks to emerge.
Docks should be targeted when are actively growing and nutrients are actively being transported to new foliage and roots. Teagasc recommends that if seed stalks are seen on the plant or if the dock has diseased leaves or is under pest attack it is better to cut/top or graze and allow re-growth of the docks before applying chemical.
Soil potassium levels should be maintained at index 3, as oversupply of potash favours the higher needs of the dock over grass. Rotating silage ground can also be an effective dock control strategy.
Michael Hennessy of Teagasc and Ivan Kelly of Teagasc recommend the use of herbicides based on dicamba, triclopyr and fluroxypyr (e.g. Dockstar Pro, Ban Dock) for season-long control of docks.
Where clover is of consequence, Eagle or Prospect may be applied. If a suitable herbicide is applied to small docks after reseeding, long term control is achieved.
Dock-infested silage swards can result in a drop of silage dry matter of up to a tonne/ acre as well as severely impairing quality.
Also, docks play havoc with baled silage. The mature stems can puncture the film, resulting in serious wastage.
The ideal time to spray is two to four weeks after nitrogen is applied when weeds should be at the correct stage for a good kill.
THISTLES
thistle family. Its roots can reach metres in length, but it also spreads by wind-blown feathery seeds during July and August. It can grow new plants from small fragments of its roots thus appearing to explode when reseeding is carried out.
They cause most damage by preventing animals grazing around them. Thistles emerge in the spring at different times so topping is a useful tactic to even up the growth stages before spraying. Teagasc recommends the use of chemicals such as 2,4-D, MCPA and dicamba to reduce top growth, but these do not translocate down to the roots. For more persistent control use Thistlex, Pastor or Forefront but follow-up sprays will be needed.
The creeping thistle can grow new plants from small fragments of its roots, thus appearing to explode when reseeding is carried out
RUSHES
According to Teagasc young, actively growing rushes of about 15cm should be targeted for treatment. These plants occur early in the growing season or four to six weeks after a mature plant has been cut.
The main chemicals licensed for rush control in grassland are MCPA and Glyphosate.. Glyphosate is a non-selective herbicide, meaning it kills any plant material it comes in contact with. It is the only product licensed for use in a weed wiper/licker.
Tight grazing may be needed before treatment. MCPA is highly soluble in water and accounts for the majority of pesticide breeches of drinking water standards. The buffer zone for MCPA is 5m (Do not spray within 5m of a water body) and can only be used in the months of March to September.
If you are in GLAS then the treatment of rushes in LIPP or THM is only spot spraying or weed licking. Therefore the only legal method to treat the rushes is by weed licking with Glyphosate.