Survey data suggests that little more than 5% of UK grassland receives a weedkiller in any given year, and few grassland farmers treat more than 10% of their pasture in any season. Weed control is a key element of grassland farming and it is important that applications of herbicides are effective, done safely and with care for the environment.
As a general rule, 1% ground cover of grassland weeds, such as Thistles and Docks, will reduce the productivity of grassland by 1%. If grassland weeds are as high as 10% then severe yield losses will occur and this will happen year on year unless a programme of weed control is planned.
Weed infestations affect the quality of silage particularly Docks and Thistles.
Grazing animals tend to avoid patches of weeds, especially thistles. As a result there is a ungrazed grass around the weed so a decrease in pasture utilisation.
Weeds pose a threat to livestock health. Injurious weeds such as Ragwort can result in illness and even death, particularly in cattle. Thistles can act as “hypodermic needles” spreading diseases such as Orf in grazing sheep and lambs.
Broadleaved weeds allow less productive grasses to invade, particularly after cutting. This results in the reduction of desirable grass species and earlier renewal of the pasture is required.
Docks (Broadleaved or Curled)
One plant can produce 60,000 seeds that are viable for up to 80 years.
Open swards as a result of poaching, over-grazing or winter kill provide space for infestations to start. Docks thrive in fertile pasture but only provide 65% of the feed value of grass from the same area.
Docks are best controlled at the rosette stage when leaves are healthy and not under stress.
Thistles (Creeping or Spear)
Creeping Thistle is a perennial weed, growing from seed or root.
Spear Thistle is a biennial growing from seed, often unnoticed in the first year due to a small rosette. Year two it can spread vigorously.
Established Creeping Thistle has extensive underground roots and competes strongly with grass.
Spear Thistle in the second year can spread to cover more than a square metre of ground seriously reducing pasture productivity. Thistles can appear at different times thus timing of control can be difficult. Treatment following topping ensures a lasting effect.
Nettles
A perennial weed that can grow from seed or rhizome.
As Nettle infestations grow they spread making pasture unpalatable reducing grazing area.
Poached and open swards will encourage Nettles to establish.
Once established, Nettles are rarely controlled by one application and require a programme of treatments.
Ragwort
Ragwort can be poisonous to stock.
Overgrazed or bare ground will encourage Ragwort establishment.
Uprooting Ragwort will not be effective as the rhizome will break off and re-grow. Ragwort is best controlled at the rosette stage
Common Chickweed
Rapid prostrate growth means it competes aggressively with grass, leading to significant losses of yield especially when establishing new leys with up to 25% reduction in silage yield.
Chickweed is a problem in re-seeds.
Creeping Buttercup
A common weed particularly in new or worn-out pastures.
Buttercup is mildly toxic and stock will not graze it. The weed will thrive in overgrazed land, especially where drainage and fertility is poor.
Soft Rush
A common weed on wet pastures.
Rushes colonise rapidly over extensive areas and reduce productivity.
Poor drainage and acid soils encourage Rush growth.
Topping Soft Rush in late spring prior to seed formation weakens the plant, which then has to re-grow. Treat re-growth when the Soft Rush is about 15cm tall for best control.
Weed Control in New Leys
Weeds in reseeds are best controlled when the grass is at the 2-3 leaf stage. Docks and Chickweed are the two most critical weeds to control in reseeds. High populations of other weeds such as Fat Hen, Charlock, Redshank and Mayweed can cause problems. It is essential to control Docks and Chickweed at the seedling stage and this is achieved by applying a herbicide before the first grazing.
Weed Control in Established Grassland
In established grassland (1-5 years) and permanent grassland the six most common weeds in order of importance are Docks, Thistles, Nettles, Chickweed, Buttercup and Ragwort. Rushes can be a problem in permanent grassland.
