Control of Grassland Weeds

Mary Roache, Teagasc Advisor, Westport.

Grassland weeds are set to escalate over the next few weeks. Rushes thrived in recent wet weather as they out competed grass on land with low soil fertility. Poached fields and poor grass growth also allowed the docks and thistles to multiply. The seeds left in your pasture since 2023 from these weeds will readily germinate and spread this year if action is not taken. To control grassland weeds we tend to focus on spraying or chemical control however, there are other non-chemical means of control and prevention. This is called “Integrated Pest Management” (IPM). With IPM we first look at other means of control rather than chemical and will largely focus on farmer practices. Using various practices such as topping, grazing management, correct soil fertility and crop rotation to prevent the level of infestation will reduce chemical usage, which is a benefit to the environment and also reduces costs. Under the Sustainable Use Directive all farmers are required to keep IPM and chemical usage records each year on their farms and these should be available for inspection. In these records there are a list of IPM controls that should be used as part of the overall control of weeds.

Rushes

The soft rush is the most common of the many rush species. It is recognised by the dense tuft of brown flowers coming from the side of the stems and a continuous white centre (pith) when the stem is peeled back. Topping and mulching should be used as first control option before considering use of herbicides. Soft rush can be controlled with MCPA or 2, 4-D, applied in June or July when growth conditions are good and weather is suitable. Strong rushes should be cut and removed before any herbicide use. Weed wiping with a Glyphosate product using a tractor or quad, has the advantage of the product being applied primarily to the target plant. It uses about 1/3 of the amount of herbicide, (compared to boom spraying) and produces much lower losses to waters. No MCPA product is allowed within 5m of any drain and it is only licenced for use in a boom sprayer.

Docks

Dock seed can remain viable for over 50 years in soil, have a large root system up to 1.5m deep, and are very opportunistic in terms of where they germinate. Open swards or swards after cutting facilitate light reaching the soil surface which allows germination. Best control of docks will be achieved when docks are actively growing and nutrients are actively being transported to new foliage and roots. 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. Use of herbicides based on active ingredients dicamba, triclopyr and fluroxypyr will give season-long control of docks plus a wide range of common grassland weeds. Where clover is of consequence choose a clover safe product.

Creeping Thistles                         

Creeping thistle is the most widespread and troublesome of the thistle family. It mainly spreads by creeping roots which can be meters in length but also spreads by wind-blown feathery seeds (July & August). To make matters worse, 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. Chemicals such as 2,4-D, MCPA and dicamba reduce top growth but do not translocate down to the roots consider also products containing fluroxypyr/triclopyr for control.

As with all pesticides abide by the product label and SUD regulations. Remember that there is no product licenced for use that can be applied on farm within a minimum of 3m of any drain or surface water and sometimes the buffer required may be more than this.