Warning new ways needed to deal with weeds in crops

If weeds and pests in arable crops are to be controlled successfully in the future a whole range of new strategies will have to be employed, speakers at an agronomy conference held yesterday warned.

The problem, an audience at Perth Racecourse heard, is two- fold. The range of active chemical ingredients available was reducing as EU approval regulations become more

“This problem has spread much more quickly”

stringent and weeds and fungal infections were building up resistance to the old chemistry at a sometimes alarming rate.

Conference organiser Hutchinsons has 25 agronomy and supply depots across England and Scotland, including a new one at Forfar, and they have noted real problems especially with weeds.

John Cussans, of agronomists Niab TAG, said that resistant black grass has now become an established problem on 16,000 farms right up the eastern side of England. He suspected there might be some as yet undetected resistant blackgrass in Scotland and warned of the need to make sure any equipment such as combines and balers brought north were very thoroughly cleaned to avoid contamination.

Scottish farmers should not be complacent either about the next threat. There were already 450 farms with an established population of pesticide resistant Italian ryegrass.

Mr Cussans said: “The numbers are smaller so far but this problem has spread muchmore quickly than resistant blackgrass. It has the potential to be a national problem and not just one for south of the border.”

Dubbing pesticide resistant chickweed as “the Scottish curse” he noted that two mutations of the weed had been identified, the most common being resistant to sulfonurea weedkillers. “The problem with resistance is the harder you look the more you find,” Mr Cussans added.

Bill Clarke, also of Niab TAG, pointed towards similar problems with fungicide resistance. Yellow rust – likely to be a problem in Scottish wheat this year thanks to early autumn sowings – was appearing in new races at an alarming rate.

The so-called “warrior race” was reckoned to have come from China and was proving to be especially aggressive. The SDHI group of chemicals was holding disease at bay especially when mixed with other active ingredients but resistance was eventually inevitable. New varieties with inbuilt defences against fungal attack had a place but generally the rate of development was too slow to keep up with natural disease mutation.

“There are a few things we can do to prolong the useful life of products including using more complex two and three-way mixes. But we will alsoneed to integrate new approaches such as biological control methods, host defence activators and plant health promoters. These may sound a bit wacky at the moment but I can assure you they will be part of the standard approach before long,” Mr Clarke said.

Roma Gwynn, of Rationale Biopesticides Strategists, is already well aware of the potential for using naturally occurring chemicals as an alternative to synthetic pesticides. There were already 100 biological products approved in the EU and manufacture was now carried out on an industrial scale. Approvals were much easier to gain but so far most of the work had been on high value fruit and vine crops. The challenge would be to apply the techniques to field scale arable crops.

PROBLEM: Weeds are building up resistance to the old chemistry at a sometimes alarming rate