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Residual herbicides should be applied early to potato crops at high rates for a strong start to programmes this spring, growers are being told. Good strategy key for effective weed control in potatoes

Residual herbicides should be applied early to potato crops at high rates for a strong start to programmes this spring, growers are being told.

Despite several high profile product withdrawals in recent years, excellent levels of early season weed control in potatoes can still be achieved by choosing the right mix of chemicals, says Agrovista agronomist Ross Barton.

Mr Barton advises on over 500ha of potatoes across Shropshire, Staffordshire, Cheshire and north Wales. He still sees Soleto (metobromuron) and metribuzin as key residual herbicides with newcomer Aclonifen an effective partner for mixes for fields with high weed burdens.

No single solution

“After analysis of weed spectrum, soil type and the variety being grown, there is rarely a standard programme to cover all situations,” he says. “The key is to utilise all the actives at your disposal and put crop safety and flexibility at the forefront of programmes.”

In Soleto and Aclonifen, there are now two pre-emergence options that offer effective solutions, says Mr Barton. Both have no soil type or varietal restrictions so building programmes around them is a good starting point.

“Soleto, with its active ingredient metobromuron, is very active in soil and is an excellent partner alongside other actives such as metribuzin and prosulfocarb. Aclonifen is also an effective tank-mix partner offering additional control of polygonum weeds in tough situations.”

Looking back to last year’s dry spring, Mr Barton believes it is important to apply residual herbicides early at high dose rates – before a contact herbicide – when dealing with some of the unusual weather patterns the UK has experienced in recent years.

Extreme weather

“With the potential for sudden and extreme weather fluctuations I advise getting residuals on as early as possible – normally 7-10 days after planting. With the contact herbicide I would then advise waiting as late as possible, just before the ridges crack, applying it as a separate spray.”

Separating the two sprays enables better overall risk management, says Mr Barton.

“The combination of Soleto and metribuzin worked extremely well in last year’s dry conditions but the varietal restrictions that come with metribuzin can be an issue and I would not advise use of metribuzin on coarse, sandy soils to avoid potential crop damage” he adds.

When it comes to contact herbicides, Mr Barton sees Gozai (pyraflufen-ethyl) as a solid choice. To optimise results, he says it should be applied on its own, at 0.4 litres/ha in a mix of no less than 200 litres/ha of water with methylated seed oil (MSO).

“If Gozai is applied at the right coverage levels with an MSO then there should be no requirement for a follow up such as rimsulfuron in over 80% of cases based on the extensive work I did with Gozai during 2019 and 2020.”

Dessication

Top of last season’s industry agenda was desiccation without diquat. Most of Mr Barton’s growers opted for a flail and spray strategy. Aided by a timely, warm dry summer, he successfully trialled several knockdown strategies and was pleased with the overall results.