Technique may fight Sclerotinia

A cultural technique developed in Canada could help UK growers reduce Sclerotinia infection in carrot crops, results of trials conducted last year on a Nottinghamshire farm by crop consultant Howard Hinds have suggested.

Clipping canopy foliage between the rows allows more air movement, which is unfavourable to disease spread. Because of the planting configuration Canadian growers use, they are able to clip between individual sets of rows.

Hinds said: "In the UK, our flat-bed system of growing carrots means that just the outside of the beds can be clipped. However, in trials last year, this was still shown to reduce infection by 50 per cent."

He said the technique could be particularly important for the carrot variety Nairobi.

Hinds also reminded growers that disease risk could be reduced by managing nitrogen use to avoid crops developing a lush canopy. "Irrigation is another factor, especially from hose reels where large droplet sizes can cause canopies to fall over," he said.

BASF field vegetable product manager Robert Storer said Sclerotinia was difficult to keep out of rotation because of its wide host range that included potatoes, spring beans, peas and cabbage.

The resting bodies produced by the pathogen as an overwintering mechanism can remain viable in soil for up to 10 years, acting as a source of new infections with every cultivation.

BASF - manufacturer of the fungicide Signum, which has on-label approval for carrots - sponsors a Sclerotinia monitoring scheme for carrots, based on the germination pattern of spores in the soil.

Hinds said: "It helps growers assess disease risk and predicts when to apply their first fungicide treatments. It is vital that the first fungicide spray is applied early before the foliage has a chance to close over and starts to senesce. Once the disease is in the crop, it is impossible to get rid of it."

- Monitoring starts in May, with reports available from from June.

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