28 August 1998

Speedy test gives enough time

to take necessary action

WHEN a Suffolk cereal grower experienced difficulties controlling blackgrass in wheat last autumn he feared it had developed herbicide resistance. So he was pleased to be asked to help with the field evaluation of a yet-to-be-launched test to give a rapid confirmation of trouble.

"Blackgrass is far more of a threat on this heavyland farm than wild oats," says David Driver who grows 24ha (60 acres) of wheat and 12ha (30 acres) of winter barley on chalky boulder clay at Stedmans Farm, Rede near Bury St Edmunds. "With a severe infestation we can easily loose 10 cwts/acre so any lack of control is a major concern."

"Normally we achieve a 99% kill of black-grass so keep on top of this aggressive weed. But when we came up against difficulties with its control in a 16-acre field earlier this year we suspected resistance. Across the rest of the farm our herbicides worked normally."

It was not the first time there had been trouble. Three years ago a high organic matter level in 2ha (5 acres) of old meadowland was blamed for poor control. Some plants were killed by herbicide when others survived and grew away as if they had not been sprayed. Seed was collected from surviving blackgrass plants and growing on tests confirmed resistance three months later.

Mr Drivers control strategy had to be reworked. But he is almost totally dependent on chemical herbicides as stale seedbeds are little help in a dry autumn.

Until five years ago the policy was to use isoproturon in a tank mix with pendimethalin (Stomp). Then the more sophisticated IPU-based mixtures such as isoproturon + simazine (Harlequin) or isoproturon + pendemethlin (Trump) were used in mixtures with contact-acting fenoxaprop-P-ethyl (Wildcat).

"As soon as we knew we had blackgrass on the farm which could survive some of the herbicides used we went back to using Avadex as a pre-emergence treatment."

Tri-allate-based Avadex sensitises blackgrass seedlings so they are more vulnerable to follow-up sprays which go on when they have 2-3 leaves. "I also use Hawk plus oil instead of the Harlequin/Wildcat combination on some of the farm. It goes on about three weeks after Avadex."

Last spring Mr Driver was aware of lack of control where Avadex and Harlequin had been used and where fop and dim herbicides had been sprayed previously. When his distributor, ProCam, offered the Novartis Quicktest he jumped at the chance of finding out quickly whether the resistant population had spread. Samples of blackgrass plants were collected and sent away for analysis.

The results, which were back within four weeks, confirmed resistance to the fops and dims. That was surprising as IPU had been used for far longer on the farm. To confirm the result part of the field was sprayed again in the spring with clodinafop-propargyl (Topik). It only killed about half of the surviving weed plants, proving the accuracy of the test.

"If I could have had the results back in January or February there would have been sufficient time to do a more effective follow-up job in the spring," Mr Driver says. "It seems the new test will prove to be valuable where it is used as soon as trouble is first suspected."

Fears of resistance spreading and the inability to use cultural control in a continuous cereals system, means he may introduce a spring crop to allow time to hit blackgrass with cultivations.

The whole farm is ploughed and by delaying the start of drilling until early October there is some time to hit grass weeds. A power harrow then prepares a stale seed and after about three weeks the land is reworked with the same tool, or spring tine harrow. Avadex is applied immediately after drilling. Because of the need for a thick and competitive crop the seedrate used for the farms Riband and Consort is 198kg/ha (180 lbs/acre).

"I was pleased to try out the new test before its commercial launch. If it provides a rapid and accurate idea of why there is poor control of grass weeds there would be time to take the necessary action in the same season to prevent yield loss," Mr Driver says.

BOX

The problem field at Stedmans Farm was one of 30 from which samples of hard-to-control grass weeds were taken between March and May for checking to evaluate the Quicktest. Until now growing on collected seed has been the only reliable way to identify resistant grass weeds. But results are not available until several months after harvest so is too slow to allow control strategies to be modified in the same season. The Quicktest results are available in just four weeks, allowing ample time for inputs to be targeted for maximum efficiency and yield protection, says Novartis.

Faster results

The problem field at Stedmans Farm was one of 30 from which samples of hard-to-control grass weeds were taken between March and May for checking to evaluate the Quicktest. Until now growing on collected seed has been the only reliable way to identify resistant grass weeds. But results are not available until several months after harvest so is too slow to allow control strategies to be modified in the same season. The Quicktest results are available in just four weeks, allowing ample time for inputs to be targeted for maximum efficiency and yield protection, says Novartis.