U.K. growers try to lower residues
In a standard disease control program, many fungicide applications are made.
Jerry Cross is in charge of entomology and plant pathology at East Malling Research, where trials to minimize residues on fruit were successful.
A “name and shame” policy by the British government several years ago prompted apple growers to make efforts to reduce the residues on their fruit.
The government does routine surveillance of residues on both British and imported produce, explained Dr. Jerry Cross, who is in charge of entomology and plant pathology at East Malling Research in Kent, England. Samples are taken from supermarket shelves and analyzed for 150 pesticide active ingredients at a government laboratory. The results are published on the Internet once a quarter.
The government has been doing this for a long time, Cross said, and until about 2002, no names were published, so that when apples with high residues were found, no one knew who produced them or where they were sold.
More recently, though, the government decided to make the results more transparent and “name and shame” the culprits by giving full details of where the samples were taken and where the apples were produced, he said. “This changed the politics of it all quite dramatically.”
One set of results was published on the front page of a national newspaper with a headline asserting that the Marks and Spencer sold fruit with the highest residues in Britain. The article ranked supermarkets in terms of incidence of residues.
This caused a change in attitudes towards pesticide residues, Cross recalled, and supermarkets began asking growers to reduce residues to below reporting limits. Reporting limits, which generally ranged from 0.02 to 0.05 milligrams per kilogram, were lower than the maximum residue limits set by law.
Most English apple growers are producing varieties that are susceptible to scab and mildew, such as Gala, Braeburn, and Kanzi. The standard control strategy is to apply fungicides every seven to ten days, often with several products in the tank, Cross said. Sprays for scab are applied from bud burst until midsummer. Mildew sprays continue until August. When sprays are applied 15 times or more a season, there’s a strong possibility of residues on the fruit at harvest.
In the 1990s, East Malling researchers had already decided to explore the possibility of growing apples with no or minimal residues. In trials, no conventional pesticides were applied during fruit development. Only sulfur was applied for scab and mildew control. Mating disruption and granulosis virus were used to control codling moth. Cross said sulfur, because it occurs naturally, has a high reporting limit and can be used liberally. Scab sprays were applied after harvest, when conventional growers would normally have given up for the year. Researchers found that scab was developing on the undersides of leaves after harvest and by applying postharvest treatments, scab pressure was reduced the following year. As a result, scab control was as good or better than with conventional treatments applied every ten days during the growing season.
Growers tend to be reluctant to respond to market demand if there is no financial reward, Cross said, but about half a dozen growers around the country followed the low-residue strategy on a commercial scale for several years and it worked out well.
Then the recession came and supermarkets lost interest in low residues. Meanwhile, analytical chemists have more sensitive equipment that can detect pesticides at very low levels, and the European Union has lowered reporting levels to 0.01 milligrams per kilogram (except for sulfur).
“The industry has put a huge effort into reducing incidence of residues but had the goal posts moved, and it’s been a demotivating factor,” Cross said. “I’m sure supermarkets would like to have apples without reportable pesticides on them, and it can be done, but it requires a serious, concerted effort.