Damaged oilseed rape crops demand extra protection

Oilseed rape crops ravaged by the huge flocks of pigeons over the winter will be more susceptible to Pollen Beetle damage this spring, and should be treated as a priority, according to Syngenta Technical Manager, Iain Hamilton. Crops held back with delayed nitrogen, to avoid canopies getting too large, have been more vulnerable to continued pigeon attacks, he adds.

HGCA research has set Pollen Beetle treatment thresholds at just five Beetles per plant for crops that have been subjected to pigeon feeding damage, or are otherwise backward or stressed, compared to 15 beetles per plant on strong crops, advises Mr Hamilton.

"The lower plant populations with hybrid oilseed rape varieties will also prove more susceptible to Pollen Beetle damage, with treatment for all these crops justified when there are five Beetles per plant, along with lower thresholds for spring sown crops," he adds. "With oilseed rape values in excess of £300 per tonne, the cost of a Hallmark Zeon treatment for Pollen Beetle control is a very worthwhile investment."

Mr Hamilton reports Hallmark Zeon remains the most cost effective low-dose option for the vast majority of UK growers. "There have been incidences of reduced efficacy from pyrethroid insecticides recorded in some localised areas of the south east and the Eastern Anglian coastal region; where growers suspect their pollen beetle control was poor in 2007 a non-pyrethroid solution should be considered from the outset this season.

"But for most of the UK, where resistance has not been found, Hallmark Zeon remains the more cost effective choice and can provide high levels of control."

In light of the potential spread of resistance, Mr Hamilton advocates growers continue to monitor crops for signs of Pollen Beetle activity after treatment; if a follow-up treatment is required, then switch to an alternative non pyrethroid option such as thiacloprid.

"Once crops pass beyond yellow bud stage the damage form Pollen Beetle feeding passes, which negates the need for follow-up treatments, although growers should remain vigilant for seed weevil and pod midge threat whilst the oilseed rape pods being set," he adds.

To achieve the best results with Hallmark Zeon, Mr Hamilton advocates application using angled nozzles, alternated to face forwards and backwards along the spray boom to deliver better all round coverage of the extended green-bud flower heads.

"The Syngenta Hawk nozzle has proven ideal with water volumes of 100 l/ha, with the Syngenta Potato nozzles better suited for higher water volumes of 150 to 200 l/ha," he reports. "The Amistar nozzle gives the best option for reducing drift that may enable more timely control of Pollen Beetle attacks this spring."