Plenum approval beats Pollen Beetle resistance
A new approval for the Syngenta insecticide, Plenum, gives oilseed rape growers the crucial opportunity to break the increasing threat of pyrethroid resistant Pollen Beetle next spring (below). The unique activity of Plenum, used extensively for aphid control in potatoes and vegetable crops, has proven extremely effective in controlling all Pollen Beetle populations.
Results of Pollen Beetle monitoring have revealed a dramatic increase in the incidence of pyrethroid resistance in 2010, with resistant beetles now found throughout the south, East Anglia, northern England and into Scotland - increasing teh risk of damage to flower buds (below). In tests, over half of beetle populations showed some resistance to pyrethroids, with up to a third showing complete resistance.
Dr Steve Ellis of ADAS and currently leading an HGCA project to address Pollen Beetle risk, acknowledges that pyrethroid resistance levels have risen significantly over the past season, and spread far more extensively across the UK. "Any new option that can help growers to manage the risk of resistance more effectively is very welcome," he adds.
Syngenta Oilseed Rape Manager, Gary Jobling (above), reports the situation has escalated over the past two seasons, following a similar scenario faced by growers in Germany and Austria. "It’s no longer a case to wait and see if pyrethroid treatments have been effective. Growers need to be tackling the issue from the outset with Plenum, to protect their crops and help to minimise further resistance developing."
Mr Jobling adds that the good news for growers is that Plenum is so effective in controlling Pollen Beetle that just 0.15 kg/ha is required – which makes it far more cost-effective than treatments containing thiacloprid. Furthermore, the active ingredient in Plenum, pymetrozine, is not a neonicotinoid, making it a good option for resistance management.
He highlights that, in oilseed rape, Plenum acts as a contact insecticide, therefore growers will have to ensure application techniques can achieve good coverage of beetles within the flower buds. The Plenum approval is for one application per crop, at the green to yellow bud stage.
"We anticipate that most growers will use Plenum as the first option when the crop is at its most vulnerable green to yellow bud stage. Providing growers can stop the damage at this time, once the crop comes into flower any further losses to feeding damage will be minimal," he says.
ADAS trials in Kent this year have shown Plenum achieved faster control of Pollen Beetle, compared to either thiacloprid or the most effective pyrethroid, lambda-cyhalothrin, with over 80% control after three days and more than 90% after seven days, compared to untreated; thiacloprid achieved 20 to 30% control over the same period.
Flower attraction
New research into insect activity in oilseed rape has shown that, once the crop starts to flower, Pollen Beetles are instinctively attracted to bright yellow open petals - where the pollen is readily accessible. Providing it is warm enough for the beetles to fly, they will be drawn to the flowering plants to feed, according to insect behavioural ecologist, Dr Sam Cook, of Rothamsted Research. In fields with uneven development, flower buds on the later-developing plants may escape relatively unscathed, as the Pollen Beetle move on to plants with open flowers. Any subsequent damage from egg-laying by female Pollen Beetle is less significant at yellow bud stage, she adds.
"Providing you can protect crops through the green bud stage and into first flowering, the losses from Pollen Beetle damage can be limited," advises Dr Cook. "Any treatments must be focussed on the green to yellow bud and aimed to protect the main stem from damage."
