The poor state of many oilseed rape crops coming out of winter makes them particularly vulnerable to attack by pollen beetle in March, warns Jon Oakley, Principal Entomologist, ADAS. "With late or patchy crops you need every pod you can grow to get a worthwhile yield, so any damage done by pollen beetles can be important."
Beetle activity tends to start during the first warm day in March (15 °C), and they start to fly into crops on the second warm day of the month - often coinciding with the green bud stage.
"They go for pollen, so if the crop is still at the green bud stage they burrow into the bud to get it. A forward crop that flowers quickly will avoid too much damage because the beetles do far less harm on open flowers. But late or patchy crops just coming into bud can get hammered if beetle numbers build up quickly," he says.
Threshold levels at green bud stage remain unchanged at 15 per plant for a good crop, 5 in backward and pigeon-damaged crops and 3 in spring crops. Last year the number of pollen beetles was the highest on record, with every crop in the southern half of the country exceeding the threshold.
"Be aware of the weather conditions conducive to beetle activity, keep an eye on the threshold and respond quickly with the sprayer before too much damage is done," Mr Oakley’s advises.
Growers are advised to also be particularly alert to rape crops which are struggling due to late drilling, poor growing conditions and pigeon or slug damage. These crops are particularly vulnerable to pollen beetle attack.
"Crops should be monitored regularly in conditions where these pests are active, not during or after rain where the risk may be underestimated," says Dave Marris, insecticides product manager with BASF.
"Once threshold is reached, an application of Contest will give excellent control of this pest. It can be mixed with Filan for Sclerotinia control with minimal hazard to bees."
