Metaldehyde remains a problem in groundwater

The molluscicide Metaldehyde is frequently found in water courses above legal limits, SPUD Agronomy director John Sarup told the Syngenta seminar, but added: "There are big peaks in September, which are not necessarily due to potatoes."

Potato growers "are happy with" the slug treatment ferric phosphate, he said, but also warned: "Cover crops can increase your slug numbers."

The rising problem of potato cysts nematode (PCN) "is pushing growers to grow potatoes where they shouldn't". With continued problems over the supply of the chemical control Vydate, Sarup suggested "wider rotations and bio-fumigants", with the use of sticky nightshade roving effective "as long as it gets established".

He added that one Lincolnshire grower who failed to test for PCN had faced "disaster" last season, and urged: "It's all about finding it, so do that straight after harvest."

On PCN, recently appointed Syngenta technical manager for potatoes Douglas Dyas, said: "You need all kinds of pest control strategies for it - you can't just rely on nematicides."

However, trials last year of Syngenta's Nemathorin embedded to depths of 10, 20 and 30cm in a Maris Peer crop on PCN-infested soil in Norfolk had shown at least a threefold increase on yield over untreated crop, and twice that of plots treated with the granular nematicide oxamyl, he added.

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