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grassland seed weeds

The UK’s grassland is always deficient in nitrogen (N), which assists with the tillering of ryegrass plants as well as overall grass health. In a new sward, a clover component will not contribute N immediately – so it is important to add fertiliser. New grass responds well to regular, light applications of N.

Control perennial weeds before seeding by spraying with a selective herbicide.

This can lead to:

Seven Habits Of Highly Effective Grassland Management

If they make up more than 30% of the sward, harrow hard to remove them.

Dig a soil assessment pit to look for compaction and plant rooting structure, which should go 30cm deep in a perennial ryegrass/ Timothy sward.

On a new ley, grazing grass too early – before a second new tiller leaf appears – can damage grass persistency. If a plant’s reserves have not been fully restored, future growth will be in jeopardy. Repetitive early grazing can permanently decrease grassland yield and persistence. Grazing grasslands at the right time is especially important through dry summer periods when plants are under stress; grazing the first new growth after a period of drought and before a tiller has two and a half new leaves in place can kill grass.

Cherish new swards like growing young stock – they are the production house of the future.

In addition, although some weeds have a small amount of nutritional value, digestibility is much lower than perennial ryegrass and the structure of the weed can discourage stock from grazing surrounding grass. To effectively control grassland weeds it is first important to understand what species are present and their individual growth habit.

Good grassland management and a knowledge of the growth habit of individual weeds (Table 1) can go a long way to reducing the weed burden. Management practices which encourage a dense competitive grass sward will reduce the risk of weed infestation, as for many seeds, the absence of light via a densely packed grass sward will stop them from germinating.


As weeds increase in size they become more difficult to control so having strategies in place to ‘nip it in the bud’ early on is advisable. This can be done easily on the grazing rotation through spot spraying as soon as the cows have finished grazing each individual paddock. In doing so, weeds are easier to spot, are likely to be actively growing (encouraging uptake of the herbicide), herbicide is used efficiently and it also gives a good excuse to re-evaluate your residuals.

Biennial weeds, such as ragwort and spear thistle, could have a significant impact on grass productivity particularly in rotational leys. The plants germinate and produce vegetative growth in the first season and them flower and die in the second.

There is a direct correlation between dock and spear thistle ground cover and grass yield every 1 per cent increase in ground cover results in a 1 per cent decrease in grass growth, according to DairyCo Research and Development Manager, Dr Debbie McConnell.

Curl leaved dock and broad leaved dock are both classed as injurious weeds (see bottom of page). Serious infestations may need to be sprayed in April /May and in August /September. If there are docks in the field that you are going to rework make sure you have killed them effectively first. A common mistake is to plough or rotovate a field with docks in. This chops up the roots the pieces of which may start to grow again making the problem much worse in the following field.

Both the creeping and the meadow buttercup are mildly poisonous if eaten fresh but are all right if eaten in hay. They tend to be most common in wet or over worked land. They can be sprayed out but in general either sorting out the drainage or encouraging the grass to grow will help smother them out naturally.

This is a weed that if it takes hold will smother the grasses and is very unpalatable. If spraying it out then it is best done at seedling stage.

Another on the injurious weeds list. These require spraying when at an early bud stage (June/July) well established thistles may need repeat spraying to control them.

These are one on the most easily recognised of the weeds. Best controlled when growing vigorously, between early May and mid September. Horses will sometimes eat nettles but you have to make sure that they are not taking over a paddock.