Think ahead when planning spring herbicide programmes

Consider your spring herbicide programme carefully to avoid carry-over of any residual activity from spring applied sulphonyl urea (SU) herbicides, particularly if it remains dry and then turns wet later on in the season, is the advice from Dick Neale, of crop production specialist Hutchinsons.

“This is particularly the case for those growers who are thinking about increasing the areas of cover crops they will grow next summer, or for those thinking of coming back into or extending their oilseed rape acreage. The value of both crops is high so it’s best to avoid compromising their establishment if avoidable,” says technical manager Dick Neale (pictured).

“This puts more signi cance on how weed control is built up in the spring to avoid residual herbicide activity carrying over,” he says. “It doesn’t mean holding o controlling the di cult weeds, but look at how ‘softer’ sulphonyl ureas (SUs) could work whilst still controlling the weeds without the long tail of residuality. It’s the ne details that will matter.”

Mr Neale points out that grassweed contacts such as SU’s Hatra (mesosulfuron-methyl + 2g/ litre iodosulfuron-methyl-sodium) and Paci ca

Plus (30g/kg mesosulfuron-methyl + 10g/ kg iodosulfuron-methyl-sodium + 50g/ kg amidosulfuron) can have long-lasting e ects in the soil, so consider this if planning to incorporate them in spring herbicide programmes where cover crops or oilseed rape is following. He explains: “We used to apply these products in the autumn and issues rarely occurred, but as their e cacy on black-grass has declined, they are now increasingly used to tackle wild oats, bromes and ryegrass with a spring application.

“Wild oats can emerge anytime from February to April, and it is when herbicides are applied later to these crops that issues can be seen in following covers and oilseed rape. “Also, broad leaved weed SU Ally Max (metsulfuron methyl + tribenuron methyl), covers a whole range of weeds and has an extended growth stage on its label so is a popular option – but it is also very persistent in the soil.” He suggests an alternative to this would be to use tribenuron methyl and thifensulfuron as a mix with no metsulfuron. “Although there is a reduced weed spectrum – there is nowhere near the same levels of persistence. “Other options would be products with actives containing orasulam and uroxpyr or orasulam and hauloxyfen-methyl.” Mr Neale notes it is also important to avoid stacking herbicides with the same active as it is easy to reach damaging levels this way without realising it. “You want to avoid levels of DFF building up as it is very residual and can form a pencil thin line in the top of the soil. When a new crop meets this, it can really knock the vigour out of it. “It’s not di cult for this to happen without realising it,” continues Mr Neale. “For example, if a pre-emergence application of Liberator ( ufenacet + di ufenican) goes on at 0.6-litres/ha, this contains 60g of DFF. “If using a split label rate then it is possible to go back on post-emergence six weeks later, which is perfectly legal and safe to do, with 0.3-litres/ha (30g DFF) making that a total of 90g DFF. “However, if Crystal ( ufenacet + pendimethalin) is also being used in the programme, DFF is often added to this – so thinking of coming back into or extending that adds in another 50g of DFF which, if then their oilseed rape acreage. The value of followed up with 0.6-litres/ha of Liberator, takes the amount of DFF up to 110g. “As it’s been dry, it’s possible that one of the applications hasn’t worked, so black-grass might be starting to come through, which means another 0.3-litres/ha Liberator (30g DFF) is added to the mix, which would bring the total amount of DFF up to a total of 140g! “This shows how important it is to scrutinise the partner contents of all products and actively utilise product sequences that reduce the overall loading of persistent actives. For example, ufenacet can be sourced with picolinafen or pendimethalin and, of course, as a straight active.” FG

litre iodosulfuron-methyl-sodium) and Paci ca

Plus (30g/kg mesosulfuron-methyl + 10g/ kg iodosulfuron-methyl-sodium + 50g/ kg amidosulfuron) can have long-lasting e ects in the soil, so consider this if planning to incorporate them in spring herbicide programmes where cover crops or oilseed rape is following. products in the autumn and issues rarely