GRASSLAND management practices such as drainage, fertility, grazing, topping and mowing are very important when it comes to controlling weeds. All of these reduce seed return while encouraging the grassland to be competitive and dense which is the key to keeping weed numbers at a level that will not impact on your grassland productivity. Perennial plants such as docks, creeping thistle etc. are genetically primed to survive via their underground root systems. These underground root systems make control very difficult and usually require repeated interventions. It may be the case that the weeds become so numerous that re-seeding is required.

Ragwort

Potentially deadly to horses, ragwort is listed as a noxious weed and the main symptom from ragwort poisoning is cirrhosis of the liver. Although largely unpalatable, ragwort may be eaten when green, particularly when other grazing is sparse. It becomes more palatable to animals when cut or sprayed as it releases sugars. Any control strategy should be based on the fact that ragwort is a biennial (lives for two years) and also that just because you killed it with a spray does not mean it cannot harm livestock. Small amounts of ragwort can be effectively pulled or dug up and safely removed. For larger numbers, sprays such as MCPA; 2, 4-D; Dicamba and Forefront provide good control but measures must be taken to avoid stock eating any dying or dead ragwort present. There is no absolute time between spraying and grazing/cutting – it’s when the ragwort is too low for animals to graze it or below the cutting bar of the mower.

Thistles

There are two main types of thistle and knowing one from the other is critical to controlling them effectively. Creeping thistle is the most widespread and troublesome thistle. It mainly spreads by creeping roots which can be metres in length but also spreads by windblown feathery seeds (July and August). The extensive root system of creeping thistle is its key mechanism of survival in your fields. Frequent topping can reduce the root reserves but will seldom eradicate the problem as root fragments can lie viable and dormant for years. 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.

The spear thistle only spreads by seed which are designed to fly long distances by wind. Each plant lives for two years producing a flatted rosette of leaves in year one and then the familiar tree-like structure in year two. Once controlled in the re-seed, it rarely is a problem in grazed fields except after poaching or other sward damage. Topping is not effective to control the growth in year one but can be carried out on the second year growth before seed is set. The plant may re-grow the following year once again requiring topping. Chemical control options are the same as for creeping thistle.

Docks

Docks are the most common and troublesome weed in grassland. Docks are perennial (live many years), have a large root system, produce many hardy seeds and are very opportunistic in terms of where they germinate. For a dock seed to germinate, the amount of light reaching the soil surface is the main limiting factor as moisture and temperature are usually adequate. When sunlight passes through green grass, some of it is absorbed by the leaf. What is not absorbed will not activate the dock seed to germinate That is why docks find it so hard to germinate in grassland.

The control of docks will be achieved in good growing conditions when docks are actively growing and nutrients are actively being transported to new foliage and roots. 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. Do not apply chemicals in a period of drought as the chemical will not be taken up by the plant leaves in sufficient quantities.

Use the highest water rates on the manufacturer’s label for best effects. CMPP/Dicamba or Fluroxypyr mixes offer short-term control of docks. For longer-term control, Doxstar Pro and Forefront T are good options as their chemicals are moved down to the roots. However, in all cases it is impossible to eradicate docks completely as the ‘hole’ left vacant by the older plant is quickly filled by new seedlings, unless there is competition from the surrounding grassland. Where clover is of consequence, Eagle or Prospect offer year-long control and reduce the effects of the docks in future years. Experiments done by Teagasc advise prioritising a post-emergence spray after re-seeding as this can give five years dock-free grass.