Bonfire night is the time to think about blackgrass. Experts say early November is the best month to start tackling this emerging troublesome grassweed.
For winter wheat drilled early in September, dry seed-beds may have impaired the performance of pre-emergence herbicides and led to a flush of blackgrass.
Agronomists say early treatment of this emerging blackgrass is key, as it will then be easier to kill.
“There is a need to get on early at the one- to three-leaf stage when there is active growth of the blackgrass,” says weed expert Sarah Cook at crop consultants ADAS.
She point out that autumn is the best time to control the weed, as by the spring it will be larger and also tillering and so more difficult to control.
Most post-emergence blackgrass treatments in wheat will be based around Atlantis or Unite, and most agronomists suggest using either of these two with a residual herbicide partner.
As these two main herbicides are largely contact in action, a residual such as pendimethalin, flufenacet or diflufenican should be added to control late-emerging weeds, says Dr Cook.
This also helps in protecting against herbicide resistance, as both Atlantis and Unite show the same type of ALS blackgrass resistance, while these residuals have a different mode of action.
Chris Cooksley, head of marketing at Bayer CropScience which makes Atlantis, agrees growers should be looking at treatments now and also use a residual partner.
“With blackgrass coming up, growers should start to first think about spraying around bonfire night,” he says.
He suggests using Atlantis with a residual such as Bayer’s Liberator at full rate, or at half rate if this product has been used earlier as a pre-emergence treatment.
- Atlantis: Iodosulfuron + mesosulfuron
- Unite: Pyroxsulam + flupyrsulfuron.
- Auxiliary: Clodinafop + prosulfocarb
- Liberator: Diflufenican + flufenacet
Mr Cooksley points that most blackgrass germinates in September and October, but still 5-10% will germinate in November and so a residual partner is important.
“It is key to apply a treatment when there is active growth, the blackgrass is small and there are good spraying conditions,” he says.
Some independent agronomists say applying Atlantis in the autumn can give a 1t/ha yield advantage over using the same herbicide in the spring.
Tom Chillcott, agronomist at Dow AgroSciences, advises that his group’s product Unite should be used at the one- to three-leaf stage and in conjunction with a residual product.
“The smaller the plant, the better the control will be, especially when applied in a period of active growth,” he adds.
He suggests using Unite in a tank mix with a residual partner such as flufenacet, pendimethalin or prosulfocarb.
Where there is a high population of blackgrass and it is growing quickly, then Dow advises adding Auxiliary to the tank mix to boost overall control.
It advises growers to walk their fields regularly and look for sign that blackgrass is actively growing before treating with a post-emergence herbicide.
In addition, Mr Chillcott says Unite has good activity on some broadleaved weeds, offers a wide range of tank mix options and has no restrictions for following crops.
Herbicide resistance to blackgrass is increasing and ADAS’s Dr Cook says if growers have serious triple-R ALS resistance then herbicide performance will be hit.
Blackgrass resistance has been confirmed in more than 2,000 farms in 32 English counties, and the situation is getting worse.
She says ADAS trials have only shown 20% control of blackgrass where triple-R resistance has been reported, and this is hardly significant in terms of long-term control of this weed.
“In these situations, growers should seriously consider ripping the crop up and starting again,“ she adds.
Dr Cook argues that with no new herbicide active ingredients on the horizon, growers need to use cultivation practices, such as delayed drilling, alongside herbicide programmes.
“The answer used to be in a can, put it on and it works. Now it does not work so well,” she adds.
Launch an early post-em herbicide attack on grassweeds