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08/02/2006
Tops for carrot disease control
Carrot growers face a new threat from Cercospora leaf blight, confirmed in the UK crop for the first time last year, reports ADAS vegetable disease specialist, Dr Kim Green. The early-hitting disease causes premature green top loss and complete collapse of the leaf canopy.
Speaking at the ADAS Syngenta Vegetable Conference this week (Wed, 8 February), Dr Green highlighted Cercospora carotae, which causes major losses in root crops in the US, was effectively controlled in field trials by a new Syngenta carrot fungicide – azoxystrobin + difenoconazole – which is currently seeking registration for the coming season.
"This was the UK's first confirmed case of Cercospora carotae, although it is possible that growers have misdiagnosed the disease as Alternaria in the past, since the symptoms are easily confused," she said. "The key difference is that Cercospora generally attacks earlier in the season and it hits developing young leaves, whilst Alternaria usually takes hold later in already dead or dying foliage."
As a result of the early attack and rapid loss of green leaf, the yield effects could be more severe. Dr Green advises growers to keep a close eye on crops for early signs of leaf or stem spotting, particularly in periods of hot weather, and have suspicious samples checked. The disease has a very fast - three to five day – cycle, which could make it difficult to stop spreading across the field if it gets established in the crop. "Alternaria fungicide programmes should help to minimise the effects of Cercospora," she added.
Carrot trials by ADAS in the eastern counties last year, initially set up to study Alternaria, showed the new azoxystrobin + difenoconazole fungicide mix achieved high levels of control against the disease; 10 to 15% greater than Amistar alone or a boscalid + tebuconazole programme; Cercospora infection in untreated plots reached nearly 20% of leaf area affected, reduced to less than 5% with the azoxystrobin + difenoconazole mixture.
The mixture has also performed very strongly against Alternaria, with ADAS trials showing infection cut from over 40% leaf area of untreated plants, to 10% using a four-spray azoxystrobin + difenoconazole programme through August and September; the best result in the trial.
Syngenta Vegetable Manager, Bruce McKenzie, warns an early collapse of the leaf canopy - whether Cercospora or Alternaria - not only limits yield, but will cause serious problems for growers looking to top lift; damage from share lifting will further reduce marketable yield. Maintaining the green leaf is crucial for maximum yield and root quality. "Starting the Alternaria programme with an azoxystrobin (Az) based fungicide can provide the best results for disease control and green leaf retention.
"This will be further strengthened by the pre-mix formulation with difenoconazole, which will also provide additional activity on Sclerotinia and control of mildew," he advised. "This introduction of difenoconazole provides carrot growers with a welcome new fungicide for disease control.
"Independent trials have shown that Az mixtures give the best results on Alternaria and also gave excellent Sclerotinia control in an SAC trial in 2005," added Mr McKenzie.
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Speaking at the ADAS Syngenta Vegetable Conference this week (Wed, 8 February), Dr Green highlighted Cercospora carotae, which causes major losses in root crops in the US, was effectively controlled in field trials by a new Syngenta carrot fungicide – azoxystrobin + difenoconazole – which is currently seeking registration for the coming season.
"This was the UK's first confirmed case of Cercospora carotae, although it is possible that growers have misdiagnosed the disease as Alternaria in the past, since the symptoms are easily confused," she said. "The key difference is that Cercospora generally attacks earlier in the season and it hits developing young leaves, whilst Alternaria usually takes hold later in already dead or dying foliage."
As a result of the early attack and rapid loss of green leaf, the yield effects could be more severe. Dr Green advises growers to keep a close eye on crops for early signs of leaf or stem spotting, particularly in periods of hot weather, and have suspicious samples checked. The disease has a very fast - three to five day – cycle, which could make it difficult to stop spreading across the field if it gets established in the crop. "Alternaria fungicide programmes should help to minimise the effects of Cercospora," she added.
Carrot trials by ADAS in the eastern counties last year, initially set up to study Alternaria, showed the new azoxystrobin + difenoconazole fungicide mix achieved high levels of control against the disease; 10 to 15% greater than Amistar alone or a boscalid + tebuconazole programme; Cercospora infection in untreated plots reached nearly 20% of leaf area affected, reduced to less than 5% with the azoxystrobin + difenoconazole mixture.
The mixture has also performed very strongly against Alternaria, with ADAS trials showing infection cut from over 40% leaf area of untreated plants, to 10% using a four-spray azoxystrobin + difenoconazole programme through August and September; the best result in the trial.
Syngenta Vegetable Manager, Bruce McKenzie, warns an early collapse of the leaf canopy - whether Cercospora or Alternaria - not only limits yield, but will cause serious problems for growers looking to top lift; damage from share lifting will further reduce marketable yield. Maintaining the green leaf is crucial for maximum yield and root quality. "Starting the Alternaria programme with an azoxystrobin (Az) based fungicide can provide the best results for disease control and green leaf retention.
"This will be further strengthened by the pre-mix formulation with difenoconazole, which will also provide additional activity on Sclerotinia and control of mildew," he advised. "This introduction of difenoconazole provides carrot growers with a welcome new fungicide for disease control.
"Independent trials have shown that Az mixtures give the best results on Alternaria and also gave excellent Sclerotinia control in an SAC trial in 2005," added Mr McKenzie.
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