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ective pre-em weed control in potatoes

Potato growers should tailor herbicide choice to weed burden and plan application strategy in advance this year for best control, advises Certis Belchim technical manager James Cheesman (pictured).

He says there are two ways to apply potato herbicides. The rst is a single application of residual products to tackle emerging weeds, mixed with a contact herbicide to take out established ones. Bene ts are that it gives time to regroup after planting, and only one pass is required with the sprayer.

However, it is carried out just a week or so before emergence, which means there is a risk of soil being drier, which can reduce the e cacy of some residual actives.

“There’s also a greater chance of emerging potatoes coming into contact with residual and contact products, particularly if weather delays application, which can knock the crop,” explains Mr Cheesman.

If time permits, a split approach is the second option. This sees a lower rate of residuals applied early as soon as the ridges have settled. Growers can then follow up closer to emergence with a top-up dose, combined with a contact product, to burn o anything that has snuck past the rst application. It also increases duration of residual control.

This is the route preferred by Mr Cheesman, who has advocated split dose weed control for a long time. Alongside the advantages outlined, it also provides an opportunity to add a greater diversity of actives into the programme without risking crop safety.

An example is pendimethalin, which must be applied at least seven days before emergence, and is strong against polygonum weeds like knotgrass, and fumitory. Used as a holding spray, it is well within this label timing restriction and helps shore up control of problem weeds ahead of the second residual-plus-contact hit.

“For a second spray, Praxim (metobromuron) is a good choice, as it can be used up to cracking of ridges. However, every e ort should be made to apply pre-emergence if using it with a partner,” he explains.

Where opting for a single application strategy, an e ective recommendation is Praxim (metobromuron) alongside a metribuzin-based product.

This combination should be teamed with a contact PPO-inhibitor product such as Gozai (pyra ufenethyl), which is ideally suited to the early season window.

“It’s much stronger on key targets such as mayweed, groundsel, chickweed, common poppy, and eld pansy compared to the other PPOinhibitor option, carfentrazone-ethyl.”

Mr Cheesman adds that the combination of soil-acting products in the Praxim-metribuzin mix gives good control of broad-leaved weeds and some grasses up to canopy closure.

Trials show Praxim is most e ective when used at rates of 2.5–3-litres/ha, with 2-litres/ha the minimum advised rate for short season crops like salads.

“Although metribuzin is a useful piece of chemistry, some varieties are sensitive to it, but Praxim has the bene t of being compatible with all soil types and varieties. So where applying to metribuzin-sensitive varieties, use Praxim alongside alternative residuals like aclonifen, prosulfocarb or pendimethalin, depending on the weed pro le being targeted,” concludes Mr Cheesman. FG