Poor pod set is causing serious concerns for oilseed rape growers in some parts of the country this season, reports NIAB oilseeds specialist, Simon Kightley. Classic pod abortion is evident in some cases, while in others, the problem is more related to a failure of bud opening on the main raceme.

"Most of the reports we've received have been from East Anglia, but we've also had indications of problems from Kent and Bedfordshire," explains Mr Kightley. "They relate to a wide cross-section of varieties and appear to be associated with crops suffering delayed or patchy establishment last autumn.

"Certainly, crops in the north which got off to a good start have never looked better. And here in Cambridge where we irrigated to secure establishment, pod set is very good," he continues.

Although he admits there is, as yet, no clear explanation for the problem, Simon Kightley is convinced there are two main factors behind it - pollen beetle and physiological stress.
 
"Pollen beetles have been a real difficulty this year," he stresses, "especially where pigeon grazing has held crops back and reduced the effectiveness of spraying. Pollen beetles are invariably more of a threat in late-flowering seasons and where there's a big spread of flowering as you get continual re-infestation after spraying. And  delayed and variable flowering has certainly been one consequence of  the highly variable crop establishment and development seen in some areas."
 
Physiological stress has undoubtedly been at work too. Late-establishing crops with small plants coming out of the winter will have been particularly challenged by above average daytime temperatures and sunshine in late April, followed by below average sunshine and above average rainfall in early May. Crops well into stem extension will probably have been able to take this in their stride, but backward ones could easily have suffered some sort of apical meristem failure.
 
"Some agronomists have also suggested poor over-winter root development may have been a factor, but to my mind, it wouldn't really account for the level of in-field variation being reported," adds Mr Kightley.
 
In any event, he doesn't believe growers should be overly worried at this stage unless their crops are very backward, pointing out that side-branching will almost certainly make-up for early pod losses on the main stem.

"Last week, I visited the NIAB strip trials at Rockingham which suffered heavy pollen beetle infestations in parts that had been badly pigeon grazed," he says. "It was most encouraging to find the early problem in these areas had completely disappeared, with strong compensatory growth from side branches clearly taking place."