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Arable

A GUIDE TO SPRING WEED CONTROL

Promising start for weed control but no room for complacency Weed control in cereals from preemergence chemistry is so far, so good.

Last year provided one of the kinder autumns in recent seasons which most farmers took advantage of to put grass weed control programmes in a strong position at the start of 2017. The main feature of the autumn was the protracted period of dry and settled weather throughout October that allowed delayed wheat drilling on any land with grass weed problems – particularly black-grass. Data from the Met Office shows that quantity of rain and days of rainfall were both lower than the average by a significant amount so farmers who held their nerve were rewarded with good drilling conditions until the end of the month. Leicestershire farmer Ben Stroud is one who decided to delay even longer than planned on problematic land to get rid of more black-grass. “I had initially planned to drill on the 15th of October but following a thorough inspection of the farm, I decided to delay longer because I didn’t think the main flush of black-grass was out of the way,” he says. Drilling started on the 20th of October with the most problematic land only being drilled in the final week of October. “Delaying further was the right decision – I kept an eye on germination in a block of land that will get spring barley and it seemed that the main flush of black-grass was around the 15th–20th of October.” All crops received a pre-em of Liberator (flufenacet + diflufenican) at 0.6-litres/ha, with some also getting 4-litres/ha of prosulfocarb at the same timing. This was followed up with a peri-emergence application of Crystal (flufenacet + pendimethalin) just as the tramlines became visible on land with a history of stubborn black-grass.

“Generally speaking, I’m very pleased with the cultivation and herbicide programme so far but spring black-grass emergence can make things problematic.” Mr Stroud expects to use a contact herbicide such as Hamlet (mesosulfuron + iodosulfuron + diflufenican) or Atlantis (mesosulfuron + iodosulfuron) on the worst areas, and in specific spots such as headlands, but the bulk of his effort has been focused on autumn residual applications and prioritising fields rather than a blanket programme across the whole farm.

So far, so good Lincolnshire AICC Agronomist Peter Brumpton (left) shares the view that it has been a good season so far: “The wider window for drilling in autumn and the good conditions meant that crops got away well with fewer problems than usual. At this stage, we can consider ourselves fortunate that crops have established well and that ground conditions are good for the time of year. “Like October, December was quite a dry month so land is not waterlogged with big areas of standing water, so people may be able to carry on with field work if conditions hold – but it is a big if and one proper spell of rain will change things completely.” According to Mr Brumpton weed control in cereals from pre-emergence chemistry is so far, so good – he doesn’t think it is the best he’s seen but the combination of late drilling,

good establishment and solid pre-em performance puts farmers in a strong position. In his area, many black-grass plants are in quite weak condition so there have been a number of post-em recommendations of Atlantis or Hamlet to take advantage of sick plants and finish them off. “Contact herbicides went on at the tail end of 2016 so we are still awaiting results. There are still some outstanding recommendations and further good weather is needed so applications can be made before small, weakened black-grass has an opportunity to recover,” he says. “In my opinion, the post-em needs to be targeted on places where it is going to deliver results – mainly where the target is weak and small. The bigger picture with black-grass control is that we are winning some battles but not the war. The situation has progressed in recent years in that we understand the problem better but lack all the tools needed to achieve total success,” he concludes.

Trials results Provisional results from Bayer herbicide trials also point to good levels of weed control so far – with more potentially still to come as the company’s Dr Gordon Anderson-Taylor (right) explains:

“At our Chishill weed screen, we drilled on the 13th of October and applied pre-emergence herbicides on the 21st of the same month. The screen is backward relative to previous seasons but it still reflects the typically late drilled situation in many regions this season. “At present, in the first week of January, black-grass is at the 1–3 leaf stage with cereals at early tillering (GS21–22). It is too early to tell the final control from any of the herbicide programmes but I would say that control from Liberator alone is at the high-end of its control range at 70–80 per cent. What’s more, it is still working so there is potential for more efficacy to come.” According to Dr Anderson-Taylor, the benefit of mix or sequence partners is less this season due to the high initial control from Liberator. However, pendimethalin and prosulfocarb gave around a 5 per cent boost and tri-allate around 10 per cent additional control. There are no results for post-emergence products yet, although the plants in these plots are looking very sick after Atlantis or Hamlet was applied on the 27th of November. Even though things look good at the moment, Dr Anderson-Taylor is keen to stress that black-grass has the capacity to fight back. “Last year, there was a highly-effective pre-em treatment but conditions allowed a small number of plants to produce a large number of heads and seeds by the time June came around. “Black-grass is still small and weakened after the pre-em programme so a follow up treatment of a Hamlet or Atlantis type product and a residual partner should give the firepower needed to get really good control of black-grass.”

Spring weed control FACTS • • •

Late drilling, good establishment and solid pre-em performance puts farmers in a strong position Spring black-grass emergence can be problematic Post-em herbicides need to be targeted on places where they are going to deliver results – mainly where the weed target is weak and small

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Farmers Guide Magazine February 2017 Issue

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Farmers Guide Magazine February 2017 Issue