DIAMOND BACK AGAIN
Diamond-back moths, the scourge of brassicas, seem to like the milder UK climate, with last year’s summer influx surviving colder weather, and pesticides, to emerge again
It was a Monday in August when Steve Foster took a call from a worried grower in Somerset. The grower was struggling to control an invasion of what looked like diamond-back moths that had laid eggs through the nets designed to protect his swede crop.
“Diamond-backs are quite an exotic moth, originally from Asia,” says Foster, an entomologist at Rothamsted Research who works on insecticide resistance in crop pests, including aphids, beetles, weevils, thrips and moths. “For our studies, I rear them at around 25 degrees [Celsius].”
But the moths are far from unknown in the UK; last year, there was an unprecedented invasion of the pests. Though poor flyers as adults, the wind can carry them long distances from the warmer climate of continental Europe; they then lay eggs and, as caterpillar larvae, can wipe out the foliage of cabbage, cauliflower, swede and other brassicas.
From samples sent by the Somerset grower, Foster confirmed that the pests were indeed diamond-back moths and set about assessing their resistance to several insecticides, as he’d done last year with three samples from Lincolnshire, Suffolk and Scotland.
Foster raised a colony through two generations, and then fed sets of the caterpillar larvae on Chinese cabbage leaves soaked in three types of pesticides: “Two compounds worked but the pyrethroid insecticide, which can work well against Lepidoptera, was again no good,” he says.
“The sample showed the same resistance profile as those of 2016, and the moths were also lighter coloured, as last year’s,” says Foster. “The indications are that last year’s moths reproduced and survived over our UK winter. And under the [swede] nets, they probably benefited from the closeted environment.”
Foster sent the findings to the Agriculture and Horticulture Development Board, a levy board funded by farmers and growers, which released them this week.
The moths’ resistance to pyrethroids and their ability to overwinter present an increasing problem. Growers need to remain alert for the presence of this pest in their crops, says Foster, particularly if the coming winter is mild.
Growers and agronomists can contact Steve Foster at Rothamsted for advice. The institute funded the diamond-back moth work in 2016; this year, a large consortium of organisations, including AHDB, is funding the operation.
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About Rothamsted Research
Rothamsted Research is the oldest agricultural research institute in the world. We work from gene to field with a proud history of ground-breaking discoveries. Our founders, in 1843, were the pioneers of modern agriculture, and we are known for our imaginative science and our collaborative influence on fresh thinking and farming practices.
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