Syngenta has signed up an anti-pest treatment developed by agrichemicals minnow Plant Health Care to fight back in generalist weedkillers, whose falling sales were at the heart of a profits downgrade last week.

The world's biggest farm chemicals group is to develop and market Plant Health's harpin protein for inclusion in its glyphosate weedkillers, for which prices have plunged thanks to competition from generic alternatives being produced in large quantities by Chinese rivals.

Mixing in harpin, could "improve crop yield and plant performance", said Ken Fister, who is in charge of Syngenta's herbicide brand management. He added that the company was looking forward to "sharing those benefits… with growers".

Last week, Syngenta noted prices of its non-selective weedkillers, which include the Touchdown glyphosate brand, "coming down sharply" in the US market as the Swiss-based group ditched hopes of a rise in full-year profits.

The warning prompted a string of downgrades which continued on Monday, when Nomura analysts cut their price target on Syngenta stock to SFr265 from SFr320, giving the shares a "neutral" rating.

'Landmark deal' 

However, the deal lifted hopes for Plant Health Care shares, which soared 11% in London.

Chief executive John Brady said that the Syngenta sign-up represented a "second landmark agreement" for harpin, which helps plants fend off nematode worms, including the cyst nematodes that are a major threat to soybean crops.

At Evolution, analyst Philip Sparks lifted his price target on Plant Health shares to 185p, and restated a "buy" rating on the stock.

The deal "bolster the company's valuation", he said, even though it was "unlikely" to have any impact on its profits for three-to-four years, with approval from US authorities likely to take three years.

"It will be some years before we can tell how popular Harpin is with farmers," Mr Sparks added.

Shares rebound

Harpin has already been licensed to Monsanto, which is using it as a seed coating.

Indeed, Plant Health Care shares tumbled by nearly one-half in two days last month to their lowest since September 2006 after it revealed hiccups in Monsanto's seed sales were lowering harpin take-up.

Monday's 14p rise to 139p means the stock has recovered more than 50% of that lost ground.

Syngenta shares closed 0.1% higher at SFr228.80.