image expired

Fusarium inoculum is already developing at several CropMonitor (www.cropmonitor.co.uk) sites across the country and the forecasted mix of showers and warm weather will provide ideal conditions for levels to build as the critical infection period at flowering approaches, says Fera plant pathologist Dr Phil Jennings.

“We have seen low levels of Fusarium culmorum at all five sites (York, Caythorpe, Morley, Andover and Cirencester) and a reasonable amount of the Microdochium species (nivale and majus) at Caythorpe and Andover, on both stem bases and the leaf layers.

“Oilseed rape debris from another site in Devon was covered in F. graminearum perithecia (fruiting bodies), so disease will be moving into the leaf layer here too,” says Dr Jennings.

“It’s unusual to see this so early – normally you’d expect it towards the end of May. The mild winter is likely to have helped the disease to persist and develop.”

Many areas could face above-average levels of ear blight if warm, showery conditions continue, says Dr Jennings. “However, soil type and locality are likely to be important as the Microdochium species and to a lesser extent F. graminearum don’t thrive in wet, heavy soils.”

A robust dose (at least half rate) of triazole spray timed at mid-flower, such as tebuconazole, prothioconazole or metconazole, has good activity against all Fusarium species.

Work carried out by Fera in the field has shown most triazoles struggle to control Microdochium species apart from prothioconazole, says Dr Jennings.

However, further laboratory tests carried out by Fera last year showed Agate (prochloraz + tebuconazole) was the most active of thirteen products tested on the Microdochium species, almost 10 times more active than prothioconazole.

Although laboratory results are not directly related to field activity this does give an idea of likely performance, says Dr Jennings. “Agate contains a robust concentration of tebuconazole to tackle fusarium and the prochloraz inclusion appears to be very effective against the two Microdochium species as well.”

Unless it remains dry throughout flowering, an ear blight spray should be applied at mid flowering (GS 63) Dr Jennings advises. “The chemistry gives about three days’ kickback activity and three days’ protection, which is normally enough to see the crop through. If the weather turns cold and flowering is extended beyond a week, as in 2012, then a repeat application may be needed.”

Further laboratory screening work carried out at NIAB TAG last year suggests Agate is at least as effective as prothioconazole in controlling F graminearum, says MAUK technical lead Dr Paul Fogg.

“Early indications from field work in the Netherlands and elsewhere in Europe appear to back these findings. That is very good news for farmers who may be struggling to obtain prothioconazole, which has been in short supply for much of the season,” he adds.

“The T3 spray reduces infection during flowering and is all about trying to ensure yield and quality if harvest is delayed. Once infection has occurred symptoms of the disease can increase very quickly and, if rainfall continues, so can levels of toxin in the grain.

“Applied at 1 litre/ha at mid flower these results suggest that Agate should be a good alternative to prothioconazole in controlling Fusarium species and better against microdochium. And, provided a robust T2 has been applied, it will top up foliar disease control very effectively as well.”