Slow development from green bud to flowering could leave oilseed rape crops exposed to pollen beetle damage for a prolonged period this season.
The warning comes from Pete Saunders, of Syngenta, who says a fortnight of cold weather and wet soils has turned what looked like being an incredibly early and forward OSR season, into something more average.
Furthermore, cabbage stem flea beetle larvae damage has been prevalent this season, says Mr Saunders, which could reduce the ability of plants to recover from pollen beetle damage.
See also: Pollen beetle on the move across the UK
He says: “This could restrict side branching, and hence plants’ ability to compensate for bud loss from pollen beetle damage.
“Pollen beetle have been on the move during warmer day temperatures, but the cold nights have kept the crop development in check.
“As temperatures warm up, oilseed rape plants are at risk of increased pollen beetle feeding activity throughout the green bud stage, as the adults burrow into flower buds in search of pollen food sources.”
According to Syngenta, OSR crops at low plant populations can withstand greater levels of pollen beetle damage, by producing side branches and secondary flowers to compensate for earlier losses.
However, this could still have implications on the evenness of pods and seed maturity at harvest, says Mr Saunders.
“The current pollen beetle treatment thresholds indicate it is the thick crops and higher plant counts which are most susceptible to damage, since they have less capability to compensate with side branches.
“Growers are advised to monitor and target these crops as a priority. Many crops were established at significantly higher seed rates this season in an attempt to mitigate flea beetle losses in autumn, and have established with high plant counts at greater risk,” he says.
Since Syngenta has identified resistance to pyrethroids across key arable areas in the UK, Mr Saunders advises growers to use a different mode of action where resistance is suspected, in order to control pollen beetle populations.
Where the pest pressure is high, he recommends applying Plenum (pymetrozine) at the green bud stage, which stops the beetles from feeding and causing further plant damage.