Carrot growers face an increased threat of Sclerotinia attack this season, following high levels of infection in oilseed rape last year – when surveys showed over 40% of crops were affected. The resulting legacy of soil-borne sclerotia, combined with the increase in min-till arable crop establishment that leaves sclerotia on the surface, will result in sustained spore release through key stages of carrot crop development this season.
Leading ADAS disease pathologist, Dr Peter Gladders, warns that, if Sclerotinia takes hold in carrot crops where the canopy has collapsed and lower leaves have started to senesce, the disease will thrive and spread in the humid conditions of decaying leaves.
"Carrot growers need to manage nitrogen inputs more effectively, to avoid too much leafy growth and keep crops standing," he advises. "And, since there is no curative option, fungicide protection need to be built up as each layer of new leaf growth emerges, starting before the canopy closes over."
Syngenta Technical Manager, Jon Ogborn, reports that trials last year demonstrated Amistar Top delivering the highest level of protection from Sclerotinia infection. A season-long programme of Amistar Top in the Dutch trials produced a 98% reduction in Sclerotinia in roots stored through to the spring, with 0.5 % of plants infected compared to 38% in untreated plots.
A conventional tebuconazole programme in the independent Innoventis trials achieved less than 40% control, whilst the boscalid+pyraclostrobin programme still resulted in nearly 10% of plants affected. "Amistar Top was the most effective treatment in the trials, which reinforces the strength of the pre-mixed azoxystrobin and difenoconazole formulation."
"With the increasing risk of infection growers can't afford to relax this year," advises Mr Ogborn. "Trials have demonstrated that the most critical timing for control of Sclerotinia is the first fungicide, which must be applied before the canopy closes over to coat the lower canopy. "Amistar Top provides growers with a very effective option for application at this critical timing. However, further applications of Amistar Top and other effective Sclerotinia active fungicides will also be needed through the season to maintain a high level of control."
While Sclerotinia is the primary target for most fungicide programmes, Alternaria remains a secondary threat that can be very damaging. UK trials in Norfolk last year confirmed the efficacy of Amistar Top on Alternaria, with a season long programme on Nairobi reducing infection by 81%. This compared favourably with the 70% and 54% control achieved with boscalid/pyraclostrobin and trifloxystrobin/tebuconazole respectively. "With additional action on Cercospora and Powdery Mildew, Amistar Top is an outstanding broad-spectrum fungicide for carrot growers," he adds.
