Effective weapons

17 March 2001

Effective weapons

New grassweed herbicides have come under the spotlight in trials conducted by Banks.

THERES a myriad of brilliant new chemicals on the horizon to aid growers in the fight against blackgrass. But good management will always remain the most effective weapon growers have, and this could become increasingly important.

This is the view from Banks Bob Mills who delivered the results of some field-scale blackgrass trials at a series of conferences recently. Chemistry was not the only criteria on trial; establishment technique also came under the spotlight at the three 10ha trial sites at St Neots in Cambridgeshire, Sudbury in Suffolk and Newbury in Berkshire. Following the current trend, the sites were all second wheats as well.

"More growers are planting successive cereal crops and min till systems seem to be the way to go, so we thought wed have a look at some criteria growers are going to have get right," recounts Mr Mills.

Half of each plot was ploughed and half disced and pressed soon after harvest and left to green up. And the St Neots site hardly needed much encouragement. "It has a very bad grassweed problem, with both sterile and soft brome, and enhanced metabolism resistant blackgrass. By the time we sprayed off just before drilling, it was a turf."

This was lesson number one: "If youre using stale seedbeds, you need to spray the green cover at three to four leaves. Dont leave it until the last minute, even if that means spraying it twice. We had a lot of trash which hampered the establishment." Eighty percent establishment was achieved on the ploughed plots, but this dropped to just 60% for the min till plots.

"Funnily enough, however, when it came to yield, there wasnt a lot of difference," Mr Mills adds. The min till plots yielded 10.4t/ha, while the ploughed plots achieved 10.5t/ha.

Best for blackgrass

The main differences were found in the herbicide trials, that criss-crossed the establishment plots. A matrix of four chemicals were used pre-emergence: Avadex (tri-allate), trifluralin, AC210 – the new herbicide from BASF – while a Lexus/Stomp mix (flupyrsulfuron-methyl and pendimethalin) was used at emergence.

Post-emergence, old chemistry was stacked up against the new: Hawk, Lexus/Stomp and isoproturon were used, along with Monitor (sulfosulfuron), the new grassweed herbicide from Monsanto, and some coded material from Bayer, not due for release for at least a year.

Avadex turned out to be the best pre-em material for blackgrass. When followed by Hawk and Lexus, the combination gave the 98% minimum control required to keep on top of a resistant blackgrass problem. The new Bayer material was the best of the new bunch, however, giving an impressive 100% control after Avadex. The best brome control was achieved by following AC210 with either Monitor or the Bayer material. Mr Mills advises growers to consider a split application of Monitor, if the target is sterile brome but a single application for soft/meadow brome.

So thumbs up for the new chemistry? "Some of the new materials coming on to the market for wheat are looking outstandingly good in all stages of resistant blackgrass. The problem is that they are all sulfonylureas. If we get resistance to these as we have to fops and dims, theres nothing else coming through. So we must look after this chemistry if were to get the best out of it – use it in mixtures and keep the emphasis on cultural control."

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