A new easy-rinse formulation of commonly-used residual herbicide, pendimethalin has been launched by BASF.

Using advanced micro-encapsulation technology, Stomp Aqua also minimises staining to sprayers, and potentially has advantages in min-till situations.

Granted approval last week, the product’s key advantages over the EC and SC formulations already on the market will be to the user, says Sarah Mountford-Smith of BASF.

Unlike the current formulations, Stomp Aqua is formulated within a polymer coating that keeps the active ingredient trapped within a capsule suspended in an aqueous solution, free from organic solvents.

The advantage of encapsulation is it makes rinsing of mixing jugs and spray cans very easy, Mrs Mountford-Smith says. “Normally with pendimethalin you get staining of mixing jugs; with this it rinses completely.”

When diluted with water in the spray tank the capsules absorb more water causing the polymer wall to expand and swell. Some rupture in the spray tank and, during the course of spraying, release the active ingredient, while others require moisture or rain to do so, she explains.

In the USA, where the formulation is already on sale, the moisture requirement is seen as a real benefit in helping the active ingredient to be available when it is most needed as the weeds germinate, she notes. “In the UK we wouldn’t expect to see the same conditions, so normally all the capsules would open soon after spraying.”

But the capsule formulation might have an advantage for min-till users, she suggests. “One of the properties of pendimethalin is it does adhere to trash and other organic matter, which can reduce efficacy. Micro-encapsulation minimises binding – the capsules seem to roll off trash into the soil where the active ingredient needs to be.

“That could really help growers using min-till, who often experience performance issues using residual herbicides in trashy seed-beds.”

So far, the firm hasn’t conducted any trials with the new formulation to test that in the field, she admits. “We’re doing some this autumn exploring that in more detail.”

But other trials indicate that performance in non-trashy conditions is comparable with other pendimethalin formulations, she adds.