Trap-cropping as an alternative to using nematicides to control potato cyst nematodes continues to show promise, according to Andy Barker of Branston, one of the two firms promoting the concept.

Zero set-aside and higher cereal prices have inevitably made it harder to justify sowing a crop specifically to induce PCN hatches ahead of potato cropping, admits Dr Barker. But ongoing research into Solanum sisymbriifolium, sold as Foil-sis (and as DeCyst by Greenvale), is encouraging and he anticipates increased uptake this season. “More than 250ha were planted in 2007 – 50% up on 2006.”

Driving the development of the idea is the threat that approval for key PCN control chemical Telone (1,3-dichloropropene) might be withdrawn, he explains. “Approval is suspended for this year and it’s no longer being supplied.”

However, manufacturer Dow has been allowed to re-submit data to back its inclusion on the EU’s Annex 1 list and is confident that it will achieve that, he adds. Contractors also have enough in stock for this season’s needs. “There’s been quite a bit of stockpiling going on.”

Meanwhile work on improving the reliability of trap cropping proceeds. Results last season, the third commercial year of Foil-sis, though satisfactory, were not as good as in 2006, Dr Barker acknowledges.

“We got really good PCN control in 2006 because the crop grew so well. We had some 6ft tall in Yorkshire.” Last year’s growing conditions were very much against the May-sown species, he points out. “It was never really warm enough.”

Although PCN trapping has proved highly successful, with potatoes as the sacrificial crop it is costly and clearly risks of multiplying the pests if not managed carefully. S sisymbriifolium, developed at Rothamsted Research in a LINK programme with Branston, Greenvale and Dutch breeder Van Dijke, is a big advance as an alternative trap crop in that its root exudates cause the nematodes to hatch, but it is fully resistant to them, he explains.

“The derogation to grow the crop on set-aside was ideal but, with the removal of compulsory set-aside and the greatly improved prices for cereals, growers are finding it difficult to include the crop in a conventional rotation.”

It is also less effective on highly organic soils, he notes. “We don’t really know why yet, but Branston doesn’t recommend it on that type of land.”

Soils must be at least 12C before sowing, and a new pre-germination seed treatment introduced last year has greatly improved the chance of the crop making enough growth to be effective from May sowings.

“It gives it a head start,” he explains. “The crop has its peak effect on nematodes six to eight weeks from sowing, though the longer it’s in the ground the better.”

New, more effective varieties from Van Dijke are also coming on stream, says Dr Barker. “They are selecting from a fairly big pool of genetic types.”

Some cold-tolerant ones may eventually permit the crop to be sown in late summer after peas or early harvested cereals, so avoiding the loss of otherwise productive land to the trap.

“At least the soils are warm then, and those varieties can take a bit of frost damage. But so far we’ve only had 60% PCN control from August sowings, which compares with up to 75% from May ones.”

The main problem is that the nematodes themselves become less active as the land cools in the autumn, he explains.

TRICKY ESTABLISHMENT IN LINCOLNSHIRE

Chris Bayliss used Foil-sis two seasons ago on some PCN “hot-spots” on the medium loam soils at Revesby Farms, near Horncastle, Lincolnshire, where he grows about 100ha (250 acres) of potatoes.

“We grew about 4ha on rotational set-aside. We GPS soil-sample all the ground and it showed we got about 70% PCN control.”

Sown at the end of April, the crop was hard to establish, but once it got going was fine and thickened up well after topping, says Mr Bayliss.

It required irrigating, which clashed with the potatoes’ need at tuber initiation, he notes.

“The question now, with set-aside gone, is where do we fit it? We really want varieties that we can sow after wheat – that’s what we’re waiting for.”