It is important to check new sown leys for any signs of weeds, as any soil cultivation will disturb the weed seed bank and spark extensive germination, advises Ryan Came-Johnson, field technical manager for Corteva Agriscience.

"A wide range of perennial and annual weeds will take advantage of increasing temperatures and a moist seedbed to germinate, including docks, thistles, chickweed, shepherd's purse, red shank and fat hen," he says. 

 "Seedling perennial weeds such as docks and thistles are more susceptible to herbicides at this stage than treating them as mature plants, so early treatment is a good option."

 Many grassland herbicides have approvals that limit their use to established grassland only, ie grass that is over one year old at time of treatment. Corteva Agriscience now has three options for use on new sown leys.

 Leystar is a good choice where thistles are a particular problem. It will also control chickweed, buttercups, dandelions, daisies, docks, mayweed, charlock and cleavers. It can be applied from 1 February to 31 August, so is ideal for spring-sown reseeds. Legumes, including all types of clover will be killed.

 Envy has a higher use rate and is best where docks, both in their seedling form and where plants might be emerging from root fragments left over from the previous sward. It also controls both common and mouse-eared chickweed, dandelions, buttercups, daisies. Applications can be made from 1 February to 30 November – so is useful where leys are reseeded in late summer and autumn. Again, this product kills clover.

 Clover-safe product

ProClova XL is a new option for use on new sown leys where clover is a key component of the seed mix. It has good clover safety and controls a wide range of broad-leaved seedling weeds. 

 For optimum results spray when overnight temperatures are forecast to be more than 8^o centigrade for a period from three days before to three days after application date. Application is spring is recommended for quicker recovery of the clover. Applications can be made between 1 April and 31July. 

 "Establishing a new sward is a significant investment, so it pays to look closely at the weeds germinating alongside the grass," says Ryan. "Choosing the right product to treat the specific problem weeds and spraying at the right time, will always be worthwhile."