Effective weed control – whether by cultural or chemical means – is an important part of grassland management. Controlling weeds can improve forage yields, quality and longevity. However, a professional approach is vital – both to optimise the benefits of weed control, and also to protect sprayer operators, the environment and the public.
This leaflet can only provide general guidance. If you need more information or advice, consult a BASIS registered agronomist or your supplier for information specific to a given farm or field. And always check the product label.
Why control weeds in grassland?
For livestock farmers, grassland offers a valuable and economic source of grazing and conserved forage. Effective utilisation of grassland is key to the profitability of livestock enterprises. Weed infestations can soon reduce productivity. Trials from the Scottish Agricultural Colleges show that a 10% weed infestation equates to a 10% yield loss. Weeds can also pose a threat to livestock health. Injurious weeds such as ragwort can result in illness, even death, particularly in equine pastures. Thistles can act as ‘hypodermic needles’ spreading diseases, such as orf, in grazing sheep and lambs. Other weeds, such as rushes and bracken, can spread over time. A small clump one year can soon take over significant areas of pasture dramatically reducing the grazing available for livestock. And for some grassland managers, it is a matter of pride to see pasture that looks well-managed, rather than a mass of unsightly weeds such as docks or thistles. Although in the right place and quantity – these broad-leaved plants are of benefit to farmland birds and insects.
Know the enemy:
DOCKS Broad-leaved dock
What is it:
One plant can produce up to 60,000 seeds, these can remain viable for up to 80 years. Why control it: Docks thrive in fertile pasture, but only provide 65% of the feed value of grass from the same area. Risk factors: Open swards: from poaching, over-grazing or winter kill all provide space for infestations to start. Weeds establish more readily on grazed land or silage systems and respond well to nitrogen fertiliser.
Treatment options:
Topping is not enough as the deep roots allow them to recover and set viable seeds. Intensive grazing or silage cutting doesn’t work as viable seeds survive ensiling and digestion.
Handy hints:
Docks are best controlled at the rosette stage when leaves are a healthy green and not under stress. When using translocated herbicides do not cut grassland for at least 21 days to allow the treatment time to work down to the roots.
THISTLES
Creeping thistle (Cirsium arvense) Spear thistle (Cirsium vulgare)
What is it:
Creeping thistle is a perennial growing from seed or portions of root as short as an inch. Spear thistle is a biennial growing from seed, often unnoticed in its first year, due to a small rosette. However, in the second year it can spread vigorously.
Why control it:
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, thus posing a serious threat to pasture productivity. Even a low infestation of just 1% will justify treatment. In addition, thistles can spread diseases such as orf in sheep and lambs.
Risk factors:
Thistles can appear at different times, thus timing of control can be difficult. Over-grazing or poor soil nutrition status can encourage growth.
Treatment options:
Where thistles are at different growth stages, topping is a useful first step in treatment. Usually, thistles in a pasture will have reached a suitable growth stage for treatment 2-3 weeks after topping
Handy hints:
Topping and treatment later in the season will ensure herbicides have a lasting effect – often beyond a season. Treatment two weeks after nitrogen application can improve herbicide uptake.
NETTLES
Nettles (Urtica dioca)
What is it:
A perennial weed that can grow from seed or root portion.
Why control it:
As nettle infestations grow they spread out making pasture unpalatable and reducing the grazing area.
Risk factors:
Poached areas and open swards will encourage nettles to establish.
Treatment options:
Nettles are best controlled when young and actively growing at 15-25cm high.
Handy hint:
Once established, nettles are rarely controlled by one treatment. Be prepared to treat regularly.
RAGWORT
Common ragwort (Senecio jacobaea)
What is it:
A perennial plant dispersed by seed and spreading root systems.
Why control it:
Ragwort can be poisonous to stock, especially horses, when it is wilting or dead.
Risk factors:
Overgrazed or bare ground can encourage ragwort establishment.
Treatment options:
Uprooting ragwort is not a reliable option as portions of root will break off and continue to grow.
Handy hint:
Once sprayed, ragwort is more palatable to grazing animals. Do not graze until treated ragwort has died off completely and been removed from the field.
CHICKWEED
Common chickweed (Stellaria media)
What is it:
The most common annual weed of grassland.
Why control it:
Rapid, prostrate growth means it competes aggressively with grass, leading to significant losses of yield especially when establishing new leys. Up to 25% reduction in silage yield has been recorded.
Risk factors:
Chickweed is often a problem in reseeds. In established pasture, it can quickly colonise bare areas, eg where mowing has ‘scalped’ the sward.
Handy hints:
Focus on good and rapid establishment of new swards. Ensure seedbeds are clean and free of perennial weeds. Use roller to ensure good seed: soil contact when sowing. Avoid over-grazing.
RUSHES
Soft rush (Juncus effusus)
What is it:
A common weed on wet pasture.
Why control it:
Rushes will soon colonise extensive areas of pasture and reduce productivity significantly.
Risk factors:
Poor drainage and acid soils will encourage rush growth.
Treatment options:
Repeated cutting at 4-8 week intervals may give some control; alternatively cutting and then treating the regrowth with a weedkiller may offer additional control. Weed wiping with glyphosate in late summer is a useful option. Rushes can be kept in check by regular topping.
Handy hint:
Check drainage and soil pH and consider remedial action if rushes appear in pasture.