"The debate is not about whether we should go pesticide free but about the risks, costs and benefits," he told the Cucumber Growers' Association conference in Peterborough. "The risk is you could lose your crop. Are the benefits worth it? If you are not getting any more money for your crop, why do it?"
He said pesticide-free cucumbers marketed by Stubbins were identified at point of retail as a premium product, but the danger was that UK growers would be pushed into pesticide-free production while the Dutch and Spanish were not. "The multiples are not going to sell the product separately so it will just fall in with the rest, hence no price difference," he explained.
Hargreaves observed that when the issue was first debated, the question was how crops could be residue-free. But as chemical analysis methods have become so much more sensitive, the level of detection has dropped.
He argued that controlling pests without residues was achievable. "The easiest way of dealing with flying pests is to trap them," he said. Whitefly is effectively controlled by Encarsia and western flower thrips by Amblyseius.
Aphis gossypii is the most difficult aphid to control because populations can quickly build up and may demand the use of pyrethrum. Spider mite can be controlled by Phytoseiulus with good monitoring, and timely sprays of Eradicote T.
Disease control is more difficult, particularly for Pythium, mildew and Mycosphaerella. "The risk to the crop of not using fungicides is considerable and few are willing to take it," said Hargreaves.
Hygiene on the grower's nursery as well as the propagator's is key to avoiding Pythium. "You need to keep plants in tip-top condition root-wise right through the crop," he added. Plant stimulants also have a role in preventing infection by both Pythium and mildew.
"I see beating Mycosphaerella as the biggest problem to being residue-free while maintaining a decent crop without recourse to conventional spraying," he said.
A Horticultural Development Company project that may improve researchers' understanding of the disease is about to start, he noted.