Better soil sampling holds key to PCN control

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Earlier and more intensive soil sampling to accurately determine Potato Cyst Nematode (PCN) risk ahead of planting is vital if growers are to beat this increasing problem, says leading agronomy group Hutchinsons.

Although many growers are routinely testing soils for PCN, John Keer of Richard Austin Agriculture says there is still considerable scope to improve procedures.

Soil sampling as early as possible can potentially make the biggest difference to managing the problem as this allows greater flexibility to alter crop rotation and grow something other than potatoes on fields where high populations are detected, says Dr Keer.

“Many people will typically be sampling from now through the winter, but quite often this means it is too late to change the rotation next spring.

“We are increasingly conducting more sampling in the preceding spring, up until the end of March or mid-April, with a view to altering cropping for the following year if the PCN population warrants it.”

Even where land is believed to be PCN-free it is still worth testing fields well ahead of planting to confirm there are no hidden issues, he adds. “This is often a problem on rented areas thought to be virgin potato land, but may have had crops or potato waste on them in the past.”

Build a long-term picture

Sampling should be more intensive to build a better picture of the overall situation and reduce the risk of missing PCN hotspots within a field. That means ensuring samples do not represent any more than 1ha, Dr Keer continues.

He also advises growers to GPS map the locations of soil samples, so that repeat future tests can be carried out on the same area to better gauge the success of changes to management practices in reducing PCN counts.

“PCN management is not about managing it over just one crop. It has got to be a rotational plan based on an accurate measure of the problem in the first place and integrates a range of control options that include nematicides, resistant varieties, cover crops and longer rotations. By using an integrated management plan it should be possible to keep levels below 5 eggs per gram.”

A similar view is shared by Hutchinsons agronomist Andrew Goodinson, who advises across 1,000ha of potatoes in Herefordshire.

“Although we’re not seeing the really high egg counts that some other regions experience – early-20s per gram is typical - PCN is an increasing problem in this area that is being spread on machinery, such as harvesters, cultivation equipment and sprayers.

andrew goodinson hutchinsons optim
“Once hotspots develop they can spread very quickly, so we have to be much more proactive in soil testing fields we suspect could be at risk. Tests are more intensive than in the past, with one sample per hectare or even one per half-hectare where we think there’s a problem.”

Mr Goodinson says even very low egg counts will warrant treatment with an integrated programme as this can prevent a more significant problem spreading. “If you have a high population, you’re better off avoiding growing potatoes on that land altogether.”

He also believes in the benefit of early soil testing for PCN, but acknowledges that in some cases – especially where land is rented - growers may not know exactly which land potatoes will be grown on until relatively late in February or early March.

PCN control key points

•    Take soil samples early to allow cropping changes
•    Aim for one sample per 0.5-1ha max
•    Map sample locations
•    Avoid spreading PCN by cleaning machinery if possible, removing volunteer potatoes, disposing of potato waste carefully
•    Use integrated control measures, including:

o    Resistant varieties
o    Longer rotations
o    Nematicides
o    Cover crops (e.g. mustard)

Alternaria has been more prolific than usual this season, especially in crops that have been under moisture stress, according to Mr Goodinson.

“There’s been hardly any blight, but lots of Alternaria. We know from previous experience that varieties such as Markies, Vivaldi, Kind Edward and Melody are susceptible, but this year we have seen it across more varieties.

“It seems to be areas of fields affected rather than whole fields and is season-related. Affected crops tend to senesce early, which means they’re losing potential yield, but it’s too early to tell the scale of any impact.”

While Mr Goodinson has achieved good results from fungicide programmes targeted at Alternaria, based on actives such as difenoconazole, mandipropamid, mancozeb and fluazinam, he is aware of others who have found the disease harder to control.

He suspects this difference may be down to variances between the two species of Alternaria; the predominant A. solani and A. alternate, although suggests more industry research is needed to better understand these differences and their impact in the field.

“We’ve sent leaf samples for analysis to try and help determine exactly what is there and plan how to control it in the future.”