At this year’s Blight Forum, experts revealed new research that suggests blight populations appear to be more aggressive, having a shorter latent period. They may also produce more spores and appear to be active at more extreme temperature.

Andy Leader, principal biologist for Dow AgroSciences, stressed that effective control combined with resistance management was the right way forward.

Leader pointed out that it is important to apply each blight fungicide at its most appropriate time. “When the haulm is growing rapidly, many growers use a systemic fungicide so that the new growth is protected. But from stable canopy onwards, they need a strong protectant fungicide with proven foliar and tuber blight activity, such as Electis,” he said.

He added that throughout the programme consideration must also be given to resistance management. “And multi-site fungicides such as mancozeb (as in Dithane and Electis) should be planned into the programme.”

According to the labels, Electis can be sprayed up to 10 times, dimethomorph + mancozeb (Invader) eight times with a maximum dose of 16 kg/ha per crop, and cyazofamid (Ranman) and benthiavalicarb-isopropyl + mancozeb (Valbon) up to six times.

Fluopicolide + propamocarb (Infinito) can be applied up to 6.4 l/ha per crop, so at 1.6 l/ha has a maximum of 4 sprays. Mandipropamid (Revus) can be used just four times.

“Fungicide resistance is an increasing concern for growers and advisors, and measures to minimise the problem should be implemented as part of an effective disease control programme,” Leader concluded. “General advice is to alternate fungicide groups within a programme, to use multi-site products more frequently and to integrate products with more than one active ingredient.”