Cereal growers looking to control blackgrass need to use a range of cultural control methods to take the pressure off herbicides and prevent weed resistance building up.
Cultural methods such as rotational ploughing, delayed drilling and going for high seed rates and competitive varieties can be used to give weedkillers a better chance of success.
“Stacking cultural control methods can get blackgrass levels down and then there is less pressure on herbicides,” said research scientist Sarah Cook at crop consultants ADAS.
Weed control is getting more difficult with fewer herbicides available, no new modes of action being seen, products being found in drinking water and weed resistance building up, she added.
Those herbicides still available need to be “protected” as the growers’ armoury against weeds is already under threat from tighter regulations, Dr Cook said.
Starting with a blackgrass seed population of 500/sq metre, Dr Cook said ploughing, delayed drilling, high seed rates and using competitive varieties cut the population to 57, giving 89% control.
“It is difficult to kill all the blackgrass with herbicides so we need to start with lower populations,” she told a Dow AgroScience cereal herbicides briefing.
Once growers have reduced weed population by cultural methods, they need to know their blackgrass resistance status and then use a robust herbicide programme, she added
Growers have the best chance in seven years to control blackgrass because of low dormancy in the weed seed, so it can be allowed to germinate and then killed off by chemical or cultural methods.
Dow says low dormancy and recent rainfall means there is good opportunity to control blackgrass by using stale seedbeds to prompt germination and then killing the weeds off before drilling.
“Those that have drilled need a pre-emergence herbicide and for those who have not drilled there is an excellent chance of stale seedbed control,” said Dow’s cereal herbicide specialist Stuart Jackson.
He says pre-emergence herbicides should be based on 240g/ha of flufenacet, and growers should consider additional residual products and use those with alternative modes of action.
Those residual partners for flufenacet could include pendimethalin, tri-allate or prosulfocarb, he added.
For post-emergence control, he suggests Dow’s Unite (pyroxsulam +flupyrsulfuron) which he says gives comparable results to rival Atlantis but gives more flexibility, such as there is no cultivation need ahead of a following crop.
Unite should be applied in a mix or sequence with a further residual product such as pendimethalin, flufenacet or prosulfocarb for best results, Mr Jackson said.
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Best chance for blackgrass control in seven years