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Arable

A GUIDE TO SPRING WEED CONTROL

Growers must focus on target weeds and application timings With agronomists and growers turning their thoughts towards spring weed control programmes, Dominic Kilburn gets the opinion of specialists from around the country on their early season plans. West In planning ahead for the first herbicide applications of the year, growers must focus on what their main weed target is and the ideal timing for the application, rather than bundling applications together to save time and money. That’s according to Herefordshire-based Hillhampton Technical Services independent agronomist Antony Wade (right) who will be targeting both brome and ryegrass in wheat at the next opportunity (likely to be in mid-February), and ahead of the T0 fungicide sprays. “If grass weeds are the target then my advice is to get on early when they are small, rather than waiting to combine the application to control a flush of broad-leaved weeds or apply in a tank mix with the first fungicides,” he explained. Antony said there was just enough moisture in the west of the country last autumn and all crops, including wheat, barley, oats and oilseed rape established well. Maize came off early too in the autumn and so wheat after that crop also went in the ground well, he added. “Most crops got sprayed up in time before Christmas although some of the residuals applied to brome and ryegrass in wheat will have had limited activity and, as some of these weeds are starting to come through now, Broadway Star (florasulam + pyroxsulam) will be the favoured product choice with activity on both.” Black-grass is an issue in the west, pointed out Antony, although at nothing like the level seen in the east of the country. “I tend to find that we can control black-grass with contact products such as Atlantis (mesosulfuron + iodosulfuron) but we now have a ‘zero tolerance’ campaign of deploying more residuals in the autumn to reduce the challenge on the contact chemistry in removing black-grass, and to try to delay the resistance build up.

“Five or six years ago meadow grass and broad-leaved weeds were the main targets in the autumn but now we are spending much more on residuals early on for the increasing grass weed problems,” he said. Broad-leaved weeds this spring will be tidied up with new chemistry in the shape of Pixxaro EC – containing the new active Arylex + fluroxypyr. It will be evaluated as it offers a different mode of action in a market where SUs traditionally dominate. “We use a lot of SUs for broad-leaved weed control and, although in the past they did a good job for us, in recent seasons we have noticed a drop off in performance. “It could of course be resistance creeping in but more likely just that they have been applied in less than ideal conditions which have predominated in the last couple of springs,” Antony suggested. A two-spray strategy is in place for charlock and runch in oilseed rape and 1-litre/ha of Fox (bifenox) will go on at the first opportunity when charlock actively grows coming out of winter, he noted. This follows on from a 0.5-litre/ha application back in mid-November that has done a reasonable initial job in most cases.

East Midlands Indigro Ltd and AICC agronomist Damian McAuley (right) said that although he is quite hopeful of low pressure from weeds this spring following successful later drilling and residual herbicide campaigns by his growers, he admits that, looking back over the past few seasons, things can be very hard to predict. “Black-grass is our number one weed and two years ago I saw lots of it over winter but it was a good spring and the residuals kept working. Last year it was a similar picture but things got a lot worse come the spring,” he explained. “We seem to be getting relatively mild winters with similar amounts of rainfall but the success, or otherwise, of weed control can be based on

so many variables such as seedbed condition at the time of drilling, soil moisture and slight changes in temperature, that it’s very hard to know what we might be facing after winter.” As in other parts of the country it was a relatively “kind” autumn for Damian with a better performance from residual chemistry later on when there was more moisture available, however with contact herbicides like Atlantis struggling to control resistant plants, he said his work on black-grass for the season was done, leaving the rest down to residual persistence and competition when cereal regrowth begins in the spring. Monitoring for broad-leaved weeds in cereals will get underway shortly although with little sign of resistance on his farms, and less use of Atlantis in the programme, SUs like Ally Max (metsulfuron + tribenuron) will be applied where appropriate, in addition to Spitfire (florasulam + fluroxypyr) and new active Arylex. Likewise, in oilseed rape, Damian is hopeful that his programmes in the autumn have put the crop on a good footing for this spring. “Blackgrass variability is down to whether there were cobbly seedbeds or not, but metazachlor based pre-ems did a god job on broad-leaved weeds and I was impressed with Centurion Max (clethodim) on black-grass when applied in early October. “In some high pressure situations we went for Crawler (carbetamide) followed by Kerb (propyzamide) but, generally speaking, Centurion Max followed by Kerb was the main treatment.” Damian highlighted that cleavers could be an issue in oilseed rape this spring as a new label for Galera (clopyralid + picloram) means it can only be used after 1st March and prior to flower buds being visible above the crop canopy. “This makes it a difficult product to use in the window available and there are also following crop restrictions limiting growers to cereals, OSR or maize for three years after application. “Quinmerac at pre-em in the autumn is a more flexible option for controlling cleavers in oilseed rape,” he added, pointing out that pre-Christmas control of thistles

with Astro Kerb (aminopyralid + propyzamide) is also his preference rather than waiting for a spring application of Dow Shield (clopyralid) that has a similarly tight application window to Galera and can miss weeds that are shaded by the crop canopy. In terms of spring crops, Damian said that most sugar beet, pea and spring bean land will receive a robust pre-emergence herbicide, depending on conditions at the time, and he noted the new approval of 0.3-litres/ ha of Liberator (flufenacet + DFF) for use on spring wheat (before 4-true leaf) would be useful as the crop is usually being grown on land notorious for black-grass as part of a rotational control strategy.

North Crops are also looking good in the north, according to Northumberland based AICC agronomist Jim Callighan (left). “We’ve been lucky,” said Jim speaking in mid-January. “In a typical season we wouldn’t have got sprayed up by now as it’s such a tight weather window up here, but this season we have managed it bar the odd late-sown field,” he commented. He said that there were a few issues back in the autumn as some of the pre-em treatments were less effective in the dry conditions and this led to brome coming through. When conditions warm a little (in March or April) then Broadway Star will be applied for brome, cleavers and wild oats. “Where we don’t have brome then Starane-type treatments will go on and new product Arylex will be a broad-spectrum option for cleaning up other spring germinating weeds.” Where black-grass is a known problem, wheat crops had a pre-em of flufenacet in the autumn and Jim will consider Hamlet (iodosulfuron + mesosulfuron + DFF) or Pacifica (iodosulfuron + mesosulfuron) in the spring. “We don’t have resistance to those products as yet and so they are our standard spring treatment for black-grass,” he said. “Where we have grass weed problems in spring barley a pre-em of pendimethalin is likely, followed up with an SU later in April,” he added. Like the wheats, oilseed rape is well established but there may be a little tidying up of the headlands with Dow Shield or Galera. ■

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