Complying with the new 10 parts per million maximum residue limit for CIPC on potatoes shouldn’t prove too difficult for growers and store managers, according to an independent potato crop consultant.

Provided growers work within label instructions, it is incredibly rare to get MRLs into double figures, David Hudson of David Hudson Potato Services says.

While the government’s Pesticide Residues Committee often finds CIPC residues on potatoes, it is usually below 5ppm, he explains.

Applying CIPC before obvious sprouting occurs will help keep residues to a minimum. “Leaving applications until there is obvious sprouting usually means higher doses and more applications will be required. Applying before sprouting means you can get away with one to three doses fewer.”

Green or damaged tubers are likely to sprout first. “If you see sprouts on those, and the crop is cured, apply CIPC as soon as possible.”

Make sure air can move easily through all parts of the stores. Wet or hot spots in stores can signify poor air movement, he explains. “There is good evidence that uneven store temperatures equals uneven distribution of CIPC.”

That can cause problems when it comes to repeat applications, with areas receiving low doses needing a further dose sooner, while there is a risk of overdosing in the high spots.

When it comes to deciding whether, and when to retreat, it is important to look for any signs of uncontrolled regrowth. “A magnifying glass can be helpful to spot fresh sprouts – look for a brown stain on sprouts that indicates CIPC is still working.”

 Low doses – good for MRLs, bad for processing crops?

Certis‘s low dose GroStop 100 CIPC product only applies 6g of active ingredient with each application, equating to 6ppm, according to the firm’s Peter Boyne.

It means any time you withdraw potatoes from store – which can be just from two days after application – you should be below the 10ppm MRL, he says.

Trials, where nine applications were made on monthly intervals to test the MRL to the limit, failed to push residues over the limit. “We didn’t see any accumulation effect.”

The firm says the product can be used either in more frequent low dose programmes or in higher doses.

British Potato Council research suggests more frequent applications of CIPC are detrimental to best processing quality. That’s not because of the CIPC, but the ethylene introduced into stores during fogging, explains BPC’s Adrian Briddon. “The more often a potato is exposed, the less good the processing quality.”

But Certis believe there should be no detrimental effects from more frequent applications, particularly if stores are vented after 6-8 hours. “Our research shows there are no adverse effects,” Mr Boyne says.