Dow AgroSciences is advising potato growers to start incorporating strong protectant foliar fungicides with known zoospore, and tuber blight activity, into their bight programmes.
Andy Leader, principal biologist for Dow AgroSciences, said: “From mid-season onwards as soon as tubers are being formed, blight sprays need to provide protection against foliar blight, as well as tuber blight.
“Zoospores are the casual agents of tuber blight and these motile spores can be produced from now on, usually when the temperatures get below 15C.”
But not all fungicides have proven activity on zoospores.
“Electis should be targeted in order to reduce the zoospore population early on before the other products are used,” said Leader. “Electis is therefore recommended from stable canopy onwards to stop zoospore formation, and then applied in sequence or blocks with other zoospore killers right up until senescence.
“The use of Electis with complementary products in a programme provides a ‘belt and braces’ approach against foliar and tuber blight.”
The approach has been upheld in trials by the British Potato Council, when, in a year where blight pressure was high, a programme consisting of two treatments of Epok, followed by Electis applied from stable canopy onwards and then alternating with Ranman TP gave the best blight control.
The choice of blight fungicide at this point in the programme makes a crucial difference to the prevention of foliar and tuber blight, and the production of a high yielding and quality crop, says Leader.
“Another important consideration of a blight spray at this point in the programme is resistance management,” he added.
“Zoxium has a different mode of action, distinct from all existing and new potato blight products. Mancozeb is a highly effective protectant fungicide with multi-site activity. Both actives in Electis complement each other in terms of the way they work.
Because the Electis label allows up to 10 sprays in any one crop, it also means that growers have the ultimate flexibility as to where, when and how they integrate this fungicide in their programmes from mid-season onwards, not the case for other fungicides.
“To prevent tuber blight, growers must protect the foliage from an early stage, use as a regular and robust blight fungicide programme with planned, early zoospore activity, and maintain this protection at and beyond desiccation.
“However, it must be appreciated that where there were low levels of foliar blight at the end of the season, there can be a high risk of tuber blight.
“You only need a few zoospores to be formed and released to the soil for tubers to suffer significant and damaging blight infections.
“The best spray programmes are those that include products with proven zoospore activity from stable canopy to senescence.”
