17 May 2002

Hybrid resister restores OSRs rotation future

Club root has been

devastating yields of

oilseed rape in north-east

Scotland and could be

taking a growing toll

further south. But a new

hybrid variety seems set to

stop the soil-borne

disease in its tracks.

Andrew Swallow reports

CLUB root can ruin oilseed rape yields as Aberdeenshire grower Bob Black knows to his cost.

But a new resistant variety has revitalised the crops future on his and many other farms in the area.

"Club root has hit us very hard in the pocket," says Mr Black who farms at Mains of Auchreddie near Ellon. "When we first noticed it, in quite a big field, a third of the crop was gone and it knocked at least 10cwt/acre off the yield."

What is more, bare patches in the field increased growing costs. "We had to go in with extra weed controls to tidy up mayweeds and chickweed growing in the gaps."

That experience prompted him to sow a trial strip of Mendel last year. The difference the club root resistant Recommended List candidate made was remarkable.

"We drilled it down a tram-line in a crop of Pronto and you could see the difference in vigour quite clearly. When we started pulling plants up, 80% of the Pronto had galls on the roots but on the Mendel there were none."

At harvest Mr Black estimates the Mendel had at least a 0.5t/ha (4cwt/acre) yield advantage over the Pronto, and this year he has sown all his 32ha (80 acres) of oilseed rape with the variety.

"The thing that is striking is how even the crop is – weve been seeing patches in our oilseed rape for years."

Compaction, waterlogging and winter-losses were thought to be to blame but now he reckons club root infection has been creeping up in the oilseed rape and winter barley based rotation.

A gas pipeline laid across the farm last summer confirmed his suspicions, soil-tests commissioned by pipeline contractors Transco showing all the fields crossed to contain club root spores. And it is not just Mr Blacks farm that is affected.

"The pipeline runs from St Fergus, north of Peterhead, to west of Aberdeen and apparently there is hardly a farm without club root in the soil." (see panel)

Scottish Agronomys Huw Phillips, who advises Mr Blacks grower group, confirms the extent of the problem in the region.

"It is not uncommon even in good fields of oilseed rape to pull up plants and find club root galls. Plants do recover sometimes, putting down another shoot, but you end up with a motley crop at harvest a bit like one that has been hammered by pigeons."

SACs Elaine Booth echoes that. "It is a problem we are seeing more and more, especially here in north-east Scotland where oilseed rape and swedes or turnips are grown," she says.

Two SAC variety trials, one near Inverness and one at Tillie Carthie, just north of Aberdeen have been hit this year.

"It wasnt our objective to get club root but it is allowing us to look at variety performance in a club root situation," she says.

At Tillie Carthie the distribution of the disease is typical, one side of the field being far worse affected than the rest. "It is perhaps where the farm has grown a strip of turnips in the past or simply fed turnips to sheep on grass down that side of the field."

All varieties bar Mendel have walnut-sized club root galls on their roots and are markedly less vigorous. But some varieties not noted as being club root resisters are showing signs of some tolerance, she notes.

"Escort looks better, but that is only on a visual assessment." Varieties susceptible to light leaf spot such as Shannon seem worst hit due to an apparent interaction between club root and the foliar disease, she adds.

Once infected, the disease survives in the soil for up to 20 years but it only thrives in acidic soils so liming may limit infection.

Recent mild, wet, autumns and earlier sowing of oilseed rape after set-aside may have added to the recent rise in incidence. Also, less vigorous control of club root carrying weeds such as shepherds purse, charlock or runch could account for some of the build up, she says.

Whatever the cause, Mr Black warns fellow growers to beware. "It is very slow to happen but when it does it hits you in the face. If it wasnt for Mendel we would have had to stop growing oilseed rape altogether." &#42

A gas pipeline across much of Aberdeenshires arable land has confirmed how widespread club root has become in the area.

Resistance revealed – the plant on the right comes from the same club root riddled soil as that on the left but theres not a gall to be seen, says SACs Elaine Booth. With no chemical control, a break from non-resistant brassicas of at least five years is essential.

&#8226 Favoured by acidic soils.

&#8226 Tight brassica rotations at risk.

&#8226 Devastates OSR yields.

&#8226 Resistant variety now available.

Pipeline figures

Of 267 fields tested along the 70km pipeline route before construction started, 36% were infected with club root, says Transco. Measures to prevent the spread of spores from infected to non-infected areas are being implemented according to DEFRA guidelines.