Control beetles to conserve rape pods
OILSEED rape could go through a relatively short, but very intense, flowering period after the recent cold snap checked crops, say experts.
This will make pollen beetle control especially important to conserve all available buds through to pod formation, according to Chris Charnock, oilseed rape technical manager for Syngenta. A short flowering period will give the crop less opportunity to compensate for bud damage caused by foraging beetles, he said.
“Growers need to be alert for the first signs of pollen beetle activity, and be ready to treat as soon as thresholds are reached at the green bud stage. The cold weather in February could have also hit beneficial predator numbers this season, which would enable pollen beetle numbers to develop quickly.”
Increasing levels of pyrethroid resistance will mean more growers using Plenum as a first option at the green bud stage, advised Mr Charnock.
Latest monitoring results from the Insecticide Resistance Action Committee (IRAC) indicate the situation has continued to deteriorate – with 75% of sampled pollen beetle populations now showing signs of resistance that will result in reduced control by pyrethroids, compared to 60% in 2010 and less than 50% the previous year.
Growers need to be targeting pollen beetle at the green bud stage, to prevent flower buds being damaged. Research suggests that beetles are actively attracted to yellow petals, so once crops are in flower remaining buds can develop relatively unscathed.
“This highlights the need to firmly focus pollen beetle control at the pre-flowering bud stage, with Plenum proving especially valuable to control any populations that may appear resistant to pyrethroid treatments.”
A further advantage of using Plenum for early pollen beetle treatment will be that growers can still retain Hallmark Zeon applications for the control of seed weevil, and reducing the effects of subsequent pod midge damage.
“While direct losses from seed weevil may be minimal, the damage it causes to pods facilitates pod midge activity that can result in far more serious losses. Targeting adult weevils with Hallmark Zeon before egg laying can thus reduce the impacts of midge.
Sprays should not be applied while bees are actively foraging in the crop.