Weed control in young grass leys should be a top priority, to maximise the value of new swards.

Having gone to the considerable expense of reseeding swards, the emergence of docks and other broadleaf weeds in new swards is a huge frustration for farmers.

Every 1% increase in ground cover by weeds in a newly established sward will decrease grass growth by 1% and, therefore, control of weeds such as docks, nettles and thistles is vital. So what steps can be taken to reduce the risks?

Not enough thought is given to planning weed control when reseeding.

When conditions are suitable for grass seeds to germinate, they are also ideal for weeds.

In fields with a large dock burden, it is recommended to spray out weeds in the year before reseeding.

Subsequently, the best time to gain 100% control of weeds is during establishment by applying glyphosate at the correct quantity and concentration.

During dry conditions in late summer and early autumn, wait for rain to ensure that the old sward is actively growing to get the best kill before reseeding.

Timing

Timing of the reseed is important, with the aim to have the new sward sown by the end of August at the latest. This will ensure that at least one grazing is achieved before winter and post-emergence weeds can be controlled in the new sward.

It is important that the glyphosate is given time to kill weeds down to the root before tilling. In autumn, a min-till method such as discing or power harrowing for reseeding grassland is necessary, and three weeks should be left between spraying and reseeding. A lot of surface trash makes it difficult to create a good seedbed to establish the sward, so applying lime will help to break down this material before reseeding. After sowing, the field should be rolled to ensure good soil to seed contact and preserve the moisture in the soil. Generally, the most effective time to control weeds in grassland is after reseeding using a post-emergence spray. Apply a post-emergence weed spray when the grass is at the two-to-three leaf stage, typically five to six weeks post sowing when the seedling dock is the size of a €2 coin.

As most seed mixes now include clover, ensuring that you use a clover-safe spray is essential and although the choice of ‘clover safe’ herbicides has been restricted in recent years, the available products are very effective when used at the correct times.

Grazing

It takes around 11 months for a new sward to fully establish, so good grazing management is very important during this early period. It is important that autumn reseeds are grazed before the first winter to encourage tillering and thicken the sward. New reseeds are ready to be grazed as soon as the plants do not pull out of the ground, at approximately 700-1,000kg DM/ha. Calves or young stock are also a good option for the first grazing, particularly if grazing conditions are poor. Graze the reseed at lower covers (1,000 kg DM/Ha) for the subsequent two grazings in the following year to allow light into the base of the sward and aid further tillering and clover establishment.