Improving sward productivity and quality through weed control

Date published: 23 April 2025

Now is an ideal time to assess and plan a sometimes-overlooked key element of the grass growing season - weed control.

Economic losses caused by weed infestation e.g. chickweed, thistles or docks, in grassland swards include competition with grass for nutrients, light and water, reduced area availability for grazing and ultimately lowering the palatability and quality of silage or hay.   

College of Agriculture, Food and Rural Enterprise (CAFRE) Beef and Sheep Adviser, Jack Friar stated: “As temperatures are starting to rise, weeds are also starting to grow, so you need to be prepared to control them as they will reach optimum stage for application quickly. A good start is to walk fields and asses them for signs of weed growth.”

Weed infestations should be measured and as a rule, for every 1% infestation of the sward, such as thistles and docks, grassland productivity and forage quality will be reduced by 1%. If weed infestation is above 10%, action should be taken.  

The best defence against weeds is ensuring the establishment of a well-managed, dense grass sward making it more difficult for weeds to establish.

Ensuring soil pH is it least 6.3 and phosphorous (P) and potash (K) levels are at the correct indices play a crucial role on promoting grass growth. Avoid over or under grazing and poaching of ground as these provide ideal conditions for weed seeds to germinate. Topping weeds is a short-term management practice and can stimulate active regrowth which results in the problem becoming worse in the longer term.

Common grassland weeds in Northern Ireland

Docks

The most common and troublesome weed in grassland, it thrives on fertile ground, especially soils with high potash levels. Jack stated: “One plant can produce up to 60,000 seeds a year, which can remain viable within the soil for 50 to 70 years.  Docks have only 65% of the feed value of grass and are unpalatable to livestock.  Cutting will not control as new shoots will regenerate.”

Spraying can be an effective treatment, with best control being achieved when docks are actively growing and transporting nutrients to new foliage and roots (Late April or early May and again in late August or early September).  Repeat sprays in same or subsequent years with products based on the active ingredients of fluroxypyr and triclopyr give much better control, but care must be taken not to exceed maximum annual dose rates.

Alternatively, clover safe sprays are also available where clover establishment and protection is important.

Chickweed

There are two types of chickweed, common chickweed (more commonly found) and mouse-eared chickweed. Common chickweed has a smooth leaf and mouse-eared chickweed has a larger leaf with a hairy surface and stem. Jack commented, “Both types of chickweed will be an issue in open or poached swards as it thrives in cool, moist conditions and can germinate and grow even at relatively low temperatures.” Products containing both active ingredients fluroxypyr and florasulam are suitable to use during early cooler spring conditions (5°C).  When temperatures start to rise a product containing fluroxypyr on its own would be a suitable option. These products will not stunt the growth of immature grass plants; however, it must be noted that these active ingredients are not clover safe. Clover safe options are available. Bare patches left after removal are ideal for more weed seeds to germinate, so ensure grass sward is established quickly to block out chickweed and other annual weeds from establishing.

Thistles

Thistles are common on older swards that are low in nitrogen and phosphorus, but high in potash. The two types of thistles are creeping (perennial) and spear (biennial). Best control is achieved when most plants are actively growing at the full rosette stage. Products based on the active ingredients triclopyr and clopyralid will give a high degree of root kill or alternatively products containing MCPA may be applied, though this will give good control of leaf growth but limited root kill. None of these listed active ingredients are clover safe. 

Ragwort

Ragwort is poisonous to livestock. Jack stated: “Small infestations can be managed by hand-pulling and ensuring root stock is removed. Regarding large infestations, spraying is highly effective.”

Ragwort should be sprayed in early spring, or as soon as there is active growth. Leaving it too late may let the plants start to shoot and control will be slower. Once sprayed, ragwort is more palatable to stock, so ensure ground is not grazed for at least 4-6 weeks after spraying to allow poisonous decaying material to die.

In conclusion: “Before using any plant protection products consult a BASIS registered agronomist for the latest information on product availability and application advice.  Anyone supplying plant protection products will have access to a BASIS qualified Adviser at the point of purchase, either directly or by phone. There will also be a helpline number on the label for technical queries,” said Jack.

Always read the label and product information before use and adhere to label recommendations regarding product application rate, cutting and grazing intervals. Anyone who uses pesticides for use in agriculture is legally required to have a Certificate of Competence in the Safe Use of Pesticides (PA1, PA2A Boom Sprayer, PA6A Knapsack etc.). 

For further advice on other grassland management or additional beef and sheep queries, please contact your local CAFRE Adviser through your DAERA Direct Office. For more information visit the Business Support area of the CAFRE website.