Broad-leaved unknowns


01 February 2022
Agronomist: 'Clean land is vital for land management'

NEW fields rented by growers as clean potato land bring new weed management challenges and agronomist Rob Ramsay has stressed the importance of starting out with clean land.

Rob, who provides agronomy on around 160ha of fresh and processing potato crops as part of 1,600ha he crop-walks in north Lincolnshire, said: "We're often up against unknowns when dealing with management of new land, in terms of weed burdens among other factors, so beginning with clean land is important. 

Rob recommends using Shark (carfentrazone-ethyl) for broadleaved weed control plans but stressed that, as with diquat, timing is key.

"While it doesn't have any grassweed activity as such, it picks up on those weeds that residual chemistry is a bit weaker on, and gives us a good, clean start to the crop, helping it to get away strongly. And if the weed burden is low, there is scope to tweak the rate a little, perhaps reducing it to 0.3 or even 0.25 litres/ha if dealing with only small weeds, which is often the case.

"Potato land rents aren't cheap, so it's important to invest what's necessary to get maximum yields. Add a residual such as Artist (flufenacet + metribuzin) or Praxim (metobromuron), plus perhaps Defy (prosulfocarb), for the addition of grassweed and further broadleaved weed control, and we have a good belt-and-braces approach for a clean start to the crop."

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Manufactured by FMC, Shark can be used alone or in in a mix with other residual herbicides when applied just prior to crop emergence and recommended application is 5-10% emergence (5% emergence on early varieties and 10% emergence on maincrop varieties) but operators should be cautious with timings, warned Jeff Fieldsend, Commercial Technical Manager at FMC.

“While application at 5-10% emergence is attractive in terms of timing flexibility, it is best to use the product as soon as the weed flush has developed and not risk applying too late, crops are moving very quickly around this time and late applications can knock them.”Jeff Fieldsend, Commercial Technical Manager at FMC

Rob said many of his customers using the same product as a diquat replacement had seen good results from well-timed applications, with the crop coming back strongly even when 5-10% has emerged. He said: "There is a fair window of application, much like there was with diquat.” 

Trials conducted by FMC and AHDB have revealed that where application is delayed onto emerged potato plants greater than 5-10%, necrotic spotting will occur, which will be quickly outgrown, leading to no long-term effects on vigour or yield.

"Mixing Shark with glyphosate allows growers to get on top of difficult weeds that glyphosate does not control when used alone,” Jeff said. “There is real improvement in the control of annual nettle, cranesbill and willowherbs with the mix and it can allow for lower rates of glyphosate to be used. A one-month interval following application exists when using this mix prior to planting a crop but this is not an issue in most situations.”

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