New higher rate for Shirlan increases blight control options

Potato growers now have more flexibility and greater power to control foliar and tuber blight, with a new approved rate of 0.4 l/ha for Shirlan applications - a 33% increase over the original 0.3 l/ha rate.

Independent Agrisearch trials with the new 0.4 l/ha rate have shown a 20% improvement in foliar blight control under high disease pressure at the canopy complete stage, compared to the original 0.3 l/ha Shirlan rate, and 33% better control than standard cymoxanil + mancozeb (Curzate) fungicide treatments. These results have been confirmed by trials at SAC in Scotland and Growscience (Agrochemex) in the eastern counties.

Syngenta Technical Manager, Jon Ogborn, reports the new 0.4 l/ha rate is recommended for situations of high or severe blight risk. "In high risk situations, where humid weather conditions have been experienced for two days, trials have shown growers operating at 10 day intervals can achieve excellent blight control with the new 0.4 l/ha Shirlan rate.

"In continued high humidity conditions and where localised blight risk is severe from dumps, volunteers, organic crops or gardens, growers can opt for 0.4 l/ha at seven day intervals, or the original 0.3 l/ha every five days," he advises.

Where there is a higher risk of tuber blight, especially with more susceptible varieties, the higher 0.4 l/ha rate may be judicious from tuber initiation onwards, according to Mr Ogborn. "Growers have incredible flexibility to use any computation of Shirlan rates, up to a total dose of 3 l/ha a season," he advises.

SAC trials last year demonstrated the value of the new higher application rate mid-season, totally eliminating any incidence of tuber blight, compared to 15 per cent in the untreated crop. Blight free yields totaled over 60 tonnes per hectare, compared to just 30 t/ha in the untreated crop.

Research in the UK and Europe has also shown Shirlan at the new 0.4 l/ha rate can achieve blight control as good as new introductions, including benthiavalicarb + mancozeb (Valbon), as well as established mid-season fungicides, such as cyazofamid (Ranman), but at lower cost. In an average of five trials, where infection hit 95% of the untreated crop, Shirlan achieved 87% blight control, compared to 80% with benthiavalicarb + mancozeb.

Independent trials in Lincolnshire by Growscience (now part of Agrochemex), demonstrated under high blight pressure that Shirlan programmes at the 0.4 l/ha rate achieved foliar blight control as good as the best available products and where Shirlan alone was used, was the only option to totally eliminate tuber blight.

Commenting on the results of his trials John Keer of Agrochemex said: "At the 0.4 rate Shirlan was extremely impressive at controlling foliar blight and is an excellent material for higher blight pressure situations. My advice to growers when blight pressure is higher is to switch to the higher rate, but not to reduce the spray interval."