Possible common scab defender outlined at Potato Council event

A promising new seed treatment was among technical topics covered at last week’s West Midlands Potato Day. Andrew Blake reports

A liquid potato seed treatment, which seems to offer useful control of common scab and help guard against seed-borne diseases, was highlighted by Syngenta’s John Ogborn at the Potato Council day sponsored by Greenvale AP, McCain and the NFU.

Coded product A8348G, based on fludioxonil as in cereal seed treatment Beret Gold, was active against seed-borne rhizoctonia, silver scurf and, uniquely for a potato seed treatment, black dot, Mr Ogborn explained.

“But the interesting thing is its activity against common scab.” The treatment was already approved in Australia for reducing that disease in the crop, and he hoped it might become UK-approved in time for next season’s plantings.

In an SAC trial last season against Amistar (azoxystrobin) and RhiNo (flutolanil), neither of which had significant effect on common scab, A8348 had usefully suppressed it, he noted.

As a liquid it would clearly involve a change of practice for growers used to applying dusts, and the company was working closely with Team Sprayers to develop a table applicator as part of an overall package.

“We’ll launch the machinery alongside it, and we won’t allow it to be used unless that’s been through an MOT and the guys applying it have had proper training.”

There was growing interest in biocontrol products to replace the dwindling numbers of agrochemical options for controlling potato diseases lurking in seed and soil, noted independent consultant Andy Barker.

Although many were once viewed by many growers as “snake oil”, the more modern materials had plenty of first-class science behind them and were well worth a try in preparation for even tighter chemical restrictions, he believed.

They included bacteria-based products such as Biomex and Fence, mycorrhizal types, and activators intended to stimulate the crop’s natural defences.

“The easiest to use are the seed treatments as they can just be tipped into the hopper. Buy an acre’s worth and give it a go.”

He foresaw a good future for biofumigation by sowing “hot” mustard crops. “Done properly it can give very good suppression of rhizoctonia, though we’ve yet to see any effect on black dot. But a lot of people have jumped on this bandwagon, and you must use specific mustard species,” warned Mr Barker.

Reduced can tillage can work for some

Potatoes can be produced satisfactorily without ploughing, and increasing fuel costs meant there was much more interest among growers in doing so, noted independent consultant Fraser Milne. But they had to understand their soils and should think carefully about what they were trying to achieve, he cautioned.

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A reduced cultivation system at Chasepool Farm has helped reduce a compaction layer that had previously built up under repeated ploughing, Fraser Milne said.

For event host, Chasepool Farm near Dudley where the soil was sandy, the main reason for switching to a Shakaerator-based system was not fuel saving. “It gives a better entry for the separator,” Mr Milne explained. “The plough leaves straw in a layer and the separator then just bulldozes.”

The farm’s reduced cultivation system, with the Shakaerator legs set relatively shallow, had also partially helped reduce a compaction layer that had built up under repeated ploughing. Deeper subsoiling, though, was clearly required to eliminate it.

However some growers were still doing far too much cultivation, using separators and bed-tillers unnecessarily, he believed. “Destoning? If you don’t have a lot of stones or clods, why do it?

Soil analysis essential

Despite recent slips in fertiliser prices soil analysis to guide nutrient inputs remained “crucial” and was highly cost-effective, according to ADAS’s Ken Smith.

“When you could be spending £800/ha it really does make sense,” he said.

Outlining trials confirming that potatoes do not respond to applying phosphate fertiliser when grown in soils at index 3 or above, Mr Smith acknowledged that some growers were unhappy unless they did so.

“OK, go ahead and do it; but then you can afford to take a holiday on the following cereals and oilseed rape.”

Livestock manures were increasingly valuable and using typical analysis figures was fine for potash and phosphorus, but their nitrogen content had to be individually assessed, he stressed. “You could be 300% out if you use standard figures.”

Testing for the N content of slurry was relatively straightforward, but assessing farmyard manures was trickier.

However, recent LINK work using the NIR technique developed from that used to analyse silage and grain was proving promising, perhaps slightly under-estimating the actual N content.

“But it’s all very well analysing it – you’ve also got to spread it evenly.” A recent tray calibration exercise showed how a faulty spread pattern could be easily corrected by adjusting the bout width, he explained.

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