After trifluralin, what have we learnt?
Agronomists across the UK are successfully coping with the loss of the residual herbicide trifluralin and have adjusted their weed control programmes in winter oilseed rape to give good weed control of difficult weeds such as poppies and cleavers.
A survey of 15 leading agronomists covering over 30,000 hectares of oilseed rape in 18 different counties indicated that the most common response to the loss of trifluralin was to increase the use of residual coformulations (53% of responses), with a further 47% indicating an increased dose rates of residual herbicides. All agronomists reported that the approach that they took was successful.
Simon Pretty, an agronomist for Agrovista, has found the weed control strategy he adopted in oilseed rape last year was very successful. "The loss of trifluralin was potentially a real blow, particularly with regard to poppy control. But a pre-emergence application of Oryx (metazachlor and quinmerac) plus clomazone plus the specialist adjuvant Grounded gave excellent results on this weed, as well as many other important weeds including cleavers and hedge mustard. This mix had all the angles covered as far as I was concerned."
He points out however that for residuals to work well you need good establishment, good soil moisture and some crop competition. "Last year in East Anglia it was dry in the autumn, but this didn’t appear to impact on the broad-leaved weed control, although control of volunteer cereals was more difficult. This year I am hoping it will be more straightforward. We have good moisture and reasonably warm soils and the rape is emerging very rapidly. My weed control plans this year will be no different to last year."
Simon says that the newly introduced restriction of a maximum of 1000 gms a.i./hectare over three years for metazachlor will have no negative impact on his herbicide plans. "In East Anglia the inclusion of sugar beet in the rotation means that oilseed rape is not grown in a close rotation. Usually rape is grown in a 1 in 4 rotation. So the approach I take allows for this."
Full rate Oryx (3 l/ha) delivers 999 gms /ha of metazachlor and 249 gms/ha of quinmerac. The metazachlor element contributes to the control of Chickweed, Dead-nettle, Groundsel, Mayweed, Shepherd’s-purse, Speedwell, Sow-thistle as well as some activity Annual Meadow-grass and Black-grass. The addition of quinmerac adds Cleavers, Common Poppy, Fool’s Parsley as well as additional effect on Red Dead-nettle and Speedwell.
According to the agronomist survey, the most frequent weeds found in winter oilseed was Black-grass (selected by 66% of respondents), poppy (40% of respondents), cleavers (40% of respondents), cereal volunteers (40%), Crane’s-bill (30%), Charlock (27%) with other weeds also being mentioned chickweed, Runch, Hedge Mustard and Thistles.
Commenting on these findings, Will Reyer, Oilseed rape Product Manager for BASF says that black-grass is expected to be even more of a problem in 2010 and remains the number one concern. "That’s not surprising considering the poor control in cereals last season. But for broad-leaved weeds the ranking of weeds according to heir importance is similar to last year, with Cleavers, Poppy and Crane’s-bill all being seen as major threats this autumn."
Will Reyer concludes that growers will always want get their oilseed rape off to a good start. "Using one of the BASF herbicides early on will help ensure a weed-free start to this important crop. Metazachlor remains central to the weed control programme, but its weed spectrum is incomplete. So other active ingredients such as quinmerac or dimethenamid-p in a coformulation will need to be added in to control the wider range of weeds that growers are facing across more variable conditions."
