A recent survey of 401 British oilseed rape farmers, conducted by the Kleffmann Group, reports that infestations of cabbage stem flea beetle have been observed on 57% of the total rape crop in the UK. In Germany where 1144 oilseed rape growers were interviewed, a significantly higher percentage of the oilseed rape area was infested with this damaging pest. In Germany 90% of the crop was reported to be infested.
Roger Pratchett of Independent Business Resource Limited, the UK agent for Kleffmann, says that the ban of the neonicotinoid seed treatments for a two year period starting in December 2013 in the UK (because of fears of their effects on bees) combined with increasing resistance to pyrethroid insecticides has led to a higher incidence of this pest in the UK this year. “In fact agronomists are seeing larvae in high numbers inside rape stems right now. The neonicotinoid seed treatments controlled the early pest infestations effectively and were used widely before the ban. High levels of cabbage stem flea beetles could also be a function of early drilling and a warm dry autumn, particularly September which was the driest on record, as these conditions favour egg laying. In this scenario, early hatching of larvae coincides with more vulnerable plants.”
The grower survey in the UK indicated that the area of oilseed rape in the ground this year was 649,000 hectares. “Growers were asked if they had seen any cabbage stem flea beetles and 43% of UK farmers said that they hadn’t noticed any infestation at all. However infestations were observed on the remaining 57% of the total rape area. Heavy pest infestations were apparent on 87,000 hectares (13% of the total), with a further 280,000 hectares (43%) showing slight to moderate infestations,” reports Roger.
Unsurprisingly insecticide application had increased to deal with the problem and in the UK their use (mainly pyrethroids) doubled. The damage in some areas was so heavy that an emergency Approval for acetamiprid (Insyst) and an EAMU for thiacloprid (Biscaya) was granted.
“But UK growers can count themselves lucky, as in Germany 90% of rape growers had a problem with cabbage stem flea beetle. Pest pressure has been increasing according to trapping information since 2012 and this year the Union for the Promotion of Oil and Protein Plants (UFOP) observed a huge presence of cabbage stem flea beetles just two weeks after sowing, causing shot hole damage to cotyledons and leaves of the rape plants.”
“In Germany the area of rape is double that of the UK and stands at 1.309 million hectares. Just 10% of rape growers in Germany said that they had not noticed any cabbage stem flea beetle infestation in their crop. Drilling down into the survey data, 388,000 hectares of rape in Germany were said to be severely affected by flea beetle. This is 30% of the total area, much higher than the 13% reported in the UK. A further 60% or 780,000 hectares were said to have a light to moderate infestation. This has led to more than four times the usual insecticide being applied,” says Mr. Pratchett.
