Herbicide active chlorotoluron makes a comeback

Chlorotoluron has been reapproved for use in cereals for early control of annual meadowgrass and a range of broad-leaved weeds.

The key herbicide was believed to be lost for good after its withdrawal as a straight product in 2010 and three years later as a co-formulation with other herbicide active ingredients.

Chlorotoluron had been used at rates of up to 3,500g/ha to control annual meadowgrass, broad-leaved weeds and other grassweeds in cereal crops.

The active being found in raw water on a regular basis triggered its withdrawal and there was a lack of data to support its continued use at lower application rates.

These lower rates would have reduced the risk the product posed to water and allowed the product to pass the aquatic risk assessment that is part of the regulatory process.

See also: Spring cropping and fallow could cut blackgrass

Makhteshim-Agan (MAUK) has invested in extensive research with the active, and revised rates and timings have enabled the active to be resurrected in the new product Tower, containing 250g/litre of chlorotoluron plus 300g/litre of pendimethalin and 40g/litre of diflufenican.

The company’s senior crop team lead, Paul Fogg, says that at the recommended rate of two litres/ha, Tower delivers 500g/ha of chlorotoluron that, with the partner actives, provides good control of annual meadowgrass and a range of broad-leaved weeds when used early in the season.

“Tower offers a simple, standalone solution to growers across 60% of UK cereal area for which meadowgrass, rather than blackgrass, is the main grassweed target.

“Its proven residual activity also controls key broad-leaved weeds, notably poppy, chickweed and mayweed affected by increasing resistance to ALS chemistry.”

Other weeds controlled include shepherd’s purse, red dead nettle, speedwell, pansies and cleavers.

Tower can be used on winter wheat, winter barley, winter rye and winter triticale. For this first season of use, it can be used early post-emergence at growth stage 10-13.

The product may not be used after the end of October and also carries an aquatic buffer restriction of 9m, although this is reduced to 1m at the top of a ditch that is dry at the time of application.

“A revised assessment will be submitted using drift reduction technology, such as 3-star Lerap nozzles, to mitigate the aquatic buffer.

“Further label developments will be introduced to make the product as flexible as possible for farmers,” says Dr Fogg.

MAUK is aware of the legacy issues surrounding chlorotoluron and surface water and the product label states early application timings away from the high-risk period that coincides with heavy late autumn and winter rainfall.

Dr Fogg also notes that the earlier timing also means growers will be tackling meadowgrass pre-tillering when plants are small.

Chlorotoluron has historically been used on varieties that are tolerant of the active ingredient, and although there are still variety restrictions in place for Tower, trials so far indicate no adverse effects on winter barley pre- or post-emergence, and no significant effects pre-emergence on wheat.

“Further work is needed to assess performance post-emergence on lighter soils, but the same product is marketed in Germany, where it has been possible to remove variety restrictions.

“We are hoping that we will be able to get to a similar position in the UK,” he explains.

MAUK says all major distributors of its products have ordered and received a limited supply of Tower, but there will not be enough quantity to satisfy the whole UK market.

However, it adds there will be enough for growers and agronomists to try to establish how best to use the product ahead of increased volumes next season.