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CAUTION IS REQUIRED WHEN CONSIDERING POLLEN BEETLE TREATMENTS
Date added: 09/05/08 |
Despite a direct correlation between insecticide inputs and yield response in oilseed rape, growers must exercise absolute caution and only treat for pollen beetle if thresholds are reached, says ProCam Group Technical Director, Dr. David Ellerton.
Caution is necessary because of the threat of widespread pyrethroid resistance, he says.
“Resistance to the pyrethroids has been confirmed in pollen beetle populations at several locations in the UK and indeed more so across Europe.
“Although these highly resistant individuals are only found in low numbers so far, they can withstand up to 5 times the normal pyrethroid dose. There is therefore a high risk of resistance building up if further selection pressure is exerted.”
Growers should keep a close eye on their rape crops and consider treating them only when thresholds are reached, he advises.
“Pollen beetles can cause significant damage to both winter and spring oilseed rape. They do so by biting into and killing buds in order to feed on pollen. Crops that are already flowering with pollen that can be easily accessed will incur minimal damage and need no treatment.”
The pollen beetle thresholds in winter oilseed rape are 15 adults per plant for a normal crop and 5 adults per plant for backward or stressed crops.
“There are some backward crops around, particularly those that have suffered pigeon damage or have low plant populations. But you must only go on once thresholds have been reached and that it is absolutely necessary to do so. Spring rape is also vulnerable and has a threshold of just 3 pollen beetles per plant,” warns Dr. Ellerton.
ProCam Group agronomist Nick Myers has analysed the financial impact of insecticide usage in oilseed rape and reports that up until last year the average number of insecticides, both autumn and spring, applied by the top 25% of farms was 2.5 applications compared to just under 2 applications for the bottom 25%.
“ProCam 4cast data also showed that a crop that received no insecticide yielded 2.8 t/ha but those that received between one and three insecticide treatments yielded around 3.5 t/ha, a 0.7 t/ha extra, valued at over £250/ha with rape at £360/tonne.
“The picture will be clouded however by the resistance issue which needs special attention this year and in the future,” Nick says.
PRM183
9th May 2008
For further information please contact David Ellerton, ProCam Ltd., Royston, Herts. Telephone: 01763 261592
Issued by Philip Hainey, Proterra Ltd., Stamford, Lincs. Telephone: 01780 756299
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