Early trial results with the only remaining soil fumigant highlight the importance of a good tilth and soil temperature when treating potato cyst nematode hot spot areas this autumn.

Potato cyst nematode (PCN) is considered the most economically damaging pest to potato crops in the UK. And, as eradication isn’t possible, experts advise that effective disease management is crucial.

“It is vital to manage PCN levels, as we will never eradicate the pest entirely,” says John Keer from independent trials firm Richard Austin Agriculture.

He says that sampling fields to monitor levels of PCN is an essential part of a strategy to effectively gain control. “Intensive field sampling enables hot spots to be identified and assists a better understanding of the PCN pressures present in fields.”

Where PCN hot spots are revealed, Metam (metam sodium) is an ideal treatment choice to bring these areas in line with PCN levels in the rest of the field, and occasionally whole fields will require treatment where PCN numbers have risen dramatically.

However, Dr Keer advises that application conditions are critical for metam. “The soil temperature must be as high as possible and the tilth should be similar to that of a fine seed-bed; this is to maximise the volatility of the methyl isothiocyanate gas within the soil.”

“The moisture goes hand in hand with the tilth; if you get one right the other will follow,” he says.

He comments that when it is possible to satisfy the correct soil conditions, then this is the time to be applying metam. But he reminds growers that it should not be seen as a “routine” application and generally only used to get PCN back into control.


Following the loss of Telone (1,3-dichloropropene), Dr Keer believes there is a greater need for research on getting the most out of metam. “Metam 510 is the only remaining soil fumigant in the industry capable of controlling PCN.

Trials are ongoing, but early results now looking promising. Metam was applied at a rate of 400 litres/ha and early indications are showing that visually, the differences in vigour are spectacular, says Dr Keer,

The treatment programme started with soil sampling identifying several hot spots with very high PCN counts.

“As a result of the PCN pressure, we treated with Metam 510 and a granular nematicide – it was a programmed approach which was necessary due to the initial high infestation levels.”

He remarks that at the levels found, it would not have been economically viable for a commercial grower to grow a crop of potatoes, but he is encouraged at the initial indications from the trial which suggest that the yield potential will be met.”

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