New molecules, new standards

16 December 2000

New molecules, new standards

The annual Brighton Crop Protection Conference is where new chemistry makes its public debut. The Crops team catches up with what the scientists have in the pipeline.

Strob action

BACK in 1992, there was much excitement at Brighton when BASF and Zeneca proudly announ-ced the first two strobilurin molecules, which eventually arrived on farm as Landmark and Amistar.

History repeated itself at the crop protection conference this year. Neck and neck, two follow-up strobs have arrived from the same companies. And the same two scientists took the platform to launch their new molecules: Dr Eberhard Ammermann from BASF, and Dr Jeremy Godwin from Syngenta, the new Zeneca/Novartis business.

Picoxystrobin is Syngentas sister molecule to azoxystrobin (Amistar). Is it better? Certainly, picoxystrobin is taken up much more quickly and its curative and protectant properties look enhanced, showing excellent control of septoria tritici, the key disease in wheat, at early timings. Uniquely, its mode of action combines the much-publicised vapour-movement benefit of trifloxystrobin (Twist) with rapid xylem systemic activity.

In terms of marketing, this would seem to put the product into a T1 or T2 slot, leaving the T3 ear position clear for Amistar. However, a triazole mix partner is likely to be needed against high risk early yellow rust, albeit at a low rate.

On barley, picoxystrobin has a stronger claim still. Its activity against rhyncho, net blotch and ramularia would appear to rival Twist, the strob which set new standards for disease control in barley this season.

The strob yield boost is just as good on wheat, and better on barley, than with the strobs currently available, according to initial company trials. Improvements in quality – notably, larger, bolder grains – are at the heart of the yield boost.

Last but not least, picoxystrobin has an excellent environmental profile, probably escaping buffer zone restrictions, similar to Amistar. Subject to PSD approval timetables, picoxystrobin could be available commercially by 2002.

BASFs new strob was launched with less fanfare, and less information, but word around the conference is that the molecule, provisionally named pyraclostrobin, is likely to have a big impact. Some distributors have already seen this strob in trials as BAS 500F, and performance is reported to be impressive.

Long lasting preventative, and powerful curative, activity against septoria tritici is ahead of BASFs best triazole, epoxiconazole, and could set a new standard in early disease control. And signs are that the strob yield boost effect could be taken to new heights, with a 6-7% yield increase over current strobs.

The difficulty for BASF will be positioning this product in the strob market place, which is currently dominated by its kresoxim-methyl/epoxiconazole mix, Landmark. Pyraclostrobin would appear to fit in as a replacement, rather than a partner product. PSD procedures permitting, pyraclostrobin should be available commercially in 2002, at the same time as picoxystrobin.

The new strains of strob-resistant mildew will not be controlled by either of these two new molecules, so guidelines on resistance management are likely to apply.

Beet nuggets

INSECTICIDAL seed treatments in sugar beet have become the norm; about 70% of pelleted seed is now sold with Gaucho (imidacloprid) seed dressing to protect against pests including virus-carrying aphids.

But could control be improved by combining two, or more, seed treatments in one pellet? Research at IACR Brooms Barn suggests it could – at least with the soil pests. Mixtures of tefluthrin (the active in Force) and imidacloprid, at lower rates than are used in the separate seed treatments, gave better control of soil pests including wireworm, symphylids, millipedes and springtails, says Dr Alan Dewar.

"Gaucho has done an excellent job – but there are some gaps with soil pests," he says. "Wireworm and springtails are cases where efficacy is limited – particularly when they are at high populations."

Mixtures of two actives in one pellet are used elsewhere in Europe. However, any reduction in rate of Gaucho would have to be weighed against a possible reduction in persistence of aphid protection.

Two new insecticides – fipronil and thiamethoxam – were also put through their paces as seed treatments. Fipronil gave problems with crop phytotoxicity and is unlikely to be developed as a sugar beet product. "Thiamethoxam was not particularly good on its own, but as with imidacloprid, did better when mixed with tefluthrin," says Dr Dewar. So might it be a useful mix partner in a seed treatment cocktail?

As yet thiamethoxam is not approved in the UK and will not be available until 2003 at the earliest, according to manufacturer Syngenta. However, the molecule is being developed elsewhere – for example, on oilseed rape as a flea beetle seed treatment in Canada, and as a cereal seed treatment in the US.

The bad news is that none of the seed treatment combinations was effective against leatherjackets. "Susceptible crops will be vulnerable to attack if gamma-HCH is withdrawn," says Dr Dewar. "At present it is still possible to use remaining stocks as a pre-drilling treatment, but post-emergence application is now banned. Its long term future for use in agriculture remains in doubt."

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