Look out for new threat to carrots

Carrot growers need to be vigilant for signs of a new disease that can cause premature green top loss and complete collapse of the leaf canopy, experts have warned.

Cercospora carotae causes major losses in root crops in the US and the first case was confirmed in the UK last year, explained ADAS vegetable disease specialist, Kim Green at an ADAS Syngenta Vegetable Conference today (8 February).

“This was the UK’s first confirmed case, although it is possible that growers have misdiagnosed the disease as Alternaria in the past since symptoms are easily confused.”

Cercospora generally attacks developing young leaves earlier in the season, while Alternaria comes in later and usually takes hold in already dead or dying foliage, she said.

Growers are urged to keep a close eye on crops for early signs of leaf or stem spotting, particularly in hot weather, and get any suspicious samples checked. The disease has a fast (three to five day) life cycle, so can spread quickly if left untreated, she warned.

“Alternaria fungicide programmes should help to minimise the effects of Cercospora.”

Dr Green said that a mix of azoxystrobin + difenoconazole (which is currently seeking registration for the coming season) gave high levels of control in field trials in eastern counties last season.

The mix reduced Cercospora infection to less than 5% of the leaf area, compared to an untreated control with 20% of the leaf area infected, she noted.