How to cope without trifluralin in oilseed rape

A survey of leading UK agronomists from both the distribution and independent sectors has indicated that the loss of trifluralin in oilseed rape this autumn will have a significant impact on their weed control strategies and that growers will have to re-adjust their weed control programmes to include herbicides containing active ingredients such as dimethenamid-p with the more traditional metazachlor.

Will Reyer, Oilseed Rape Product Manager for BASF, explained that 23 of the leading agronomists in the UK were interviewed from 22 different counties and covering at least 50,000 hectares of winter oilseed rape. "Nearly 40% of these advisors said that the loss of trifluralin in oilseed rape would be extremely significant, with a further 35% saying it would be quite significant. Only one agronomist thought it would be of no significance."

"Over a quarter of them (26%) had used trifluralin in every herbicide treatment that they had recommended. The most common approach (39% of respondents) was to include trifluralin in around half of all the recommendations these agronomists were writing up for weed control in winter rape."

When asked what impact the loss of trifluralin would have, the survey concluded that the major impact would be increased costs of weed control, cited by 83% of those interviewed. One agronomist said that "trifluralin was used to be on the safe side and because it was cheap." Another commented that "trifluralin was cheap and cheerful."

The next most important factor arising from the loss of trifluralin was a reduction in Poppy control, reported by 16 of the agronomists interviewed (70%). Reduction in black-grass control and the loss of an alternative herbicide group was cited by a further 13 agronomists each, accounting for 57% of the sample.

This reflected in the answers given to the question on the top weeds in winter oilseed rape. The top weeds were reported to be Black-grass (74% of the sample), Poppy (61%), Cleavers (57%) and Charlock (48%). Other weeds were Sow-thistle (39%), Hedge Mustard (13%), Mayweeds (9%), Runch (9%) and Rye-grass (9%).

When asked what weeds are becoming more of a problem, Crane’s-bill was top of the list with 48% of agronomists choosing this weed, followed by Black-grass (39%), Poppy (39%) and Charlock (35%).

Another key outcome of the agronomists survey was to gauge how trifluralin would be replaced in the oilseed rape programme. The most frequent answer given was to use higher dose rates of residual herbicides (18 out of the 23 interviewed or 78% of the sample.) Nearly half said that they would be using more advanced metazachlor co-formulations (48%). Anecdotal comments included "I will be beefing up my herbicide choice and using broader-spectrum herbicides such as Shadow or Nimbus" and "I will be upgrading my herbicide choice and move towards Katamaran Turbo from Novall plus trifluralin."

Will Reyer concludes that the loss of trifluralin will undoubtedly have an impact on this year’s weed control programmes. "With weed competition being so critical to the early establishment of the crop, we can still turn to a range of highly effective options from which to choose."

He points out that metazachlor is still central to the weed control programme, but its weed spectrum is incomplete. "Products such as Novall and Springbok include additional active ingredients which allow them to control a wider range of weeds across more variable conditions. Novall draws on the benefits of quinmerac, adding Cleavers and Poppy activity, while Springbok includes dimethenamid-p which helps especially on Crane’s-bill and Shepherd’s purse. Shadow contains three actives, metazachlor, quinmerac and dimethenamid-p and is the most complete solution available."

Will Reyer concludes that last year being the last autumn for applications of trifluralin as well as being one of the worst with regard to establishment for a number of years, growers will want to return to winter oilseed rape and make sure that they get their crops in early and off to a good start. "Using one of the BASF herbicides early on will help ensure a weed-free start to this important crop."