22 August 2001

A super Stomp

A new active ingredient – to partner pendimethalin – promises a synergistic boost to autumn weed control. Tom Allen-Stevens reports

YOU cant beat a good partnership. Diflufenican has proven to be tremendously successful when mixed with isoproturon in products such as Panther.

Now theres a new duo looking to muscle in on Panthers patch. BASF has launched PicoPro, which contains the new active ingredient picolinafen. Its from a whole new family of actives called the aryloxypicolinamides. Action is contact. It works by inhibiting carotenoids which transfer energy in the plant to chlorophyll. Unable to use up the excess energy, the plant cell self-destructs.

This has a quick and visible effect in the field, says Adam Burnhams, BASFs European crop manager for cereal herbicides. "Pendimethalin usually takes 22 days to give 80% control of cleavers. With the addition of picolinafen, this is speeded up to just six days, with complete kill achieved in 22 days."

Pendimethalin, now reaching middle age, has been given a new twist and a higher profile now that it is twinned with picolinafen. "Its an extremely effective mixing partner for broad-spectrum weed control," adds Mr Burnhams, who also claims that glasshouse studies have shown that the mixture has synergy.

This is something of a holy grail for chemists: a pair of herbicides that when mixed together are more effective at combating weeds than the sum of the two on their own. It is not a new concept: references to synergies in formulations date back to 1967 and there have been plenty since.

But whether a product is synergistic or not has been hotly disputed. "There have been many occasions when the definition of a synergistic product has been publicly debated. Scientists agree to disagree on the matter," says Peter Sutton, team leader on weed science at Jealotts Hill.

PicoPro may be the first cereal herbicide in the UK to be promoted as synergistic, however. Synergies noticed in the glasshouse are difficult to prove and even more difficult to quantify in the field, so manufacturers have tended to shy away from relying on a quality that could be challenged. "Weve certainly noticed the clodinafop in Hawk boosts the efficacy of trifluralin, but Im always a bit sceptical when I hear claims about synergy. It could have more to do with wetters, additives or other formulation factors," says Syngenta technical manager Pat Ryan.

BASF says the synergy claim was not made lightly, however. There is a mathematical formula that is generally accepted to define whether a pair of actives is truly synergistic or just complementary (the strengths of one active matches the weaknesses of the other). A lot of time, effort and money went into verifying that picolinafen has synergy with a number of potential partners, says the company.

Synergies aside, this new duo does look as though it is going to give DFF a run for its money: "PicoPro has a very similar efficacy and effect on a broad spectrum of weeds for a similar-priced dose rate. The two are virtually interchangeable," says Masstocks technical manager Clare Bend, who has carried out trials on the new product.

"It does bring a nice flexibility on weed size, too. This means you can bring the product on to farm with the confidence of knowing that if you miss the ideal spray timing, it will still be effective. This is becoming an increasingly important requirement."

It is also broad spectrum, with cleaver control claimed to be its major forte and fumitory a welcome target for northern growers. It is not going to be your first line of defence against blackgrass, but Ms Bend has noticed it is a very compatible product in the spray tank and benefits from the addition of other autumn herbicides. "It has a weakness on groundsel and annual meadowgrass. I would suggest adding flupyrsulfuron (Lexus) or Quantum (tribenuron-methyl) for better groundsel control. IPU gives it a boost for bigger annual meadowgrass control."

Another major advantage is that picolinafen is less residual than DFF. "There are no following crop restrictions, which is a big benefit in beet rotations and means you dont have to plough before a non-cereal crop," says Ms Bend.

Approval for PicoPro has already been granted by the Pesticide Safety Directorate, which means it will be available to growers this autumn. And BASF promises there are new partnerships in the pipeline. "Weve published or filed the results of 33 different mixtures with picolinafen and this is just the start of a family of new products," says Mr Burnhams.