SIDE-STEP

24 April 1999




SIDE-STEP

SCLEROTINIA

Is sclerotinia a risk this year? Debbie Beaton asks the oilseed rape specialists.

TAKE no chances say the experts. Having seen sclerotinia devastate crops in the past, independent crop consultant Johan Zethraeus will be using routine protectants against the disease in crops this season.

And with many crops flowering earlier than normal, that first spray at petal fall is approaching quickly. The end price of oilseed rape occupies Mr Zethraeuss mind when it comes to choosing product: "With oilseed rape at only £120/t we cannot afford to spend much – but Carbendazim at first petal fall does a very good job," he says. Where the crop has extended flowering a second treatment may be necessary.

Sclerotinia treatment is not necessary where the disease has never been found in fields and where the rotation is such that the disease cannot take hold because of lack of host crops. He points out that oilseed rape that has been grown for a long time, in a one-in-three year rotation for instance, is at high risk.

Sclerotinia specialist Dr John Davies at ADAS Terrington endorses his concerns adding that crops infected with sclerotinia in the last really bad year of 1991/92 will be at high risk. "Crops in those fields – and neighbouring ones – should be protected," he warns .

Growers should judge the decision to use sprays on previous history and current cropping, suggests Dr Davies. Unfortunately a Canadian-developed petal test, in which the disease on the petals is grown in a medium, has not been successful in helping to forecast sclerotinia risk. "The test takes at least 10 days in the UK because botrytis has to be ruled out in the culture," explains Dr Davies. In Canada botrytis is not an issue, so any infection can be put down to sclerotinia and allows them to provide the grower with a quicker forecast service.

However, HGCA-funded work is helping MAFF to produce a rapid petal test which can quantify inoculum on each petal. Problems in producing an antibody that does not cross react with botrytis are now being overcome, reports the CSLs Dr Judith Turner. The ELIZA technique will assess the amount of fungus present on the petal – and within one day.

Breeders are hoping to have the final answer to sclerotinia by producing a a variety without petals. Dr Eddie Arthur at John Innes explains the theory: "The main reason behind the research is that petals reflect 50-60% of light. This light is prevented from penetrating to lower pods of canopy. Take petals away and more light can reach the lower canopy, and improve yields."

Three genes responsible for suppressing petal production have been isolated and transferred into commercial lines. But the resulting crosses do not always yield a variety without petals, explains Dr Arthur. "The apetal genetic background is more complicated than just these three genes, but we are optimistic about identifying the key components."


Carbendazim

Ronilan (vinclozolin)

Konker (vinclozolin + carbendazim)

Folicur (tebuconazole)

Bayer UK413 (tebuconazole + carbendazim)

Sportak 45 EW (prochloraz)

Sportak Alpha HF, Novak (prochloraz + carbendazim)

Rovral (iprodione)

Compass (iprodione + thiophanate-methyl)


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