While perennial grassland weeds such as docks, thistles and ragwort may be clearly visible above slow-growing grass due to dry weather, now is not the time to spray them with herbicide, advises Andy Bailey, principal biologist for Corteva agriscience.

“Deep-rooted weeds can reach water supplies that grass plants cannot and this is the reason they have carried on growing in the drought conditions,” says Mr. Bailey.

“However, even the weeds are adapting to moisture stress by making physiological changes, closing the pores on the underside of their leaves and creating more wax across the leaf surface. This makes it harder for any sprays to enter the plant and work effectively, so there is no point in doing it.”

Mr. Bailey recommends farmers make a note of what, and where, the worst weed infestations are, so that targeted herbicide applications can be made later in the year, when rainfall comes back.

“A lot of the weeds, like docks and thistles have now run to seed so will need topping before spraying. After this, and once we have had some rain, new leaves will emerge, enabling much better levels of control from products such as DoxstarPro or Thistlex.

“Where ragwort is the issue, farmers should bear in mind that chopped and wilted ragwort becomes more attractive and palatable to livestock, but is poisonous and can cause liver problems. Keep all animals out of the field until any plant residues have decayed or been removed.”

Pictured: Deeper-rooted perennial weeds stay greener for longer than shallower-rooted grass