As early planted crops reach the stable canopy stage and blight pressure mounts, Dow AgroSciences is advising potato growers to start incorporating strong protectant foliar fungicides with known zoospore and hence tuber blight activity into their blight programmes.
"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 causal agents of tuber blight and these motile spores can be produced from now on, usually when the temperatures get below 15ºC. But not all fungicides have proven activity on zoospores. Zoxium in Electis stops their formation and release. Other fungicides act on zoospores once they are released. For instance fluazinam in Shirlan paralyses zoospore flagella, cyazofamid in Ranman inhibits zoospore respiration and fluopicolide in Infinito disrupts membrane proteins in zoospores. So Electis should be targeted in order to reduce the zoospore population early on before the other products are used. 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," comments Andy Leader, Principal Biologist for Dow AgroSciences.
"The use of Electis with complementary products in a programme provides a "belt and braces" approach against foliar and tuber blight. This approach has been confirmed in British Potato Council trials. In a year where blight pressure was high, these trials showed that a programme consisting of two treatments of Epok (mefenoxam plus fluazinam), followed by Electis applied from stable canopy onwards and then alternating with Ranman TP (cyazofamid plus adjuvant) up until desiccation gave the best control of both foliar and tuber blight," explains Mr. Leader.
According to Andy, the choice of blight fungicide at this point in the programme makes a crucial difference to the successful prevention of foliar and tuber blight and the production of a high yielding and quality crop. "Another important consideration of a blight spray at this point in the programme is resistance management. 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 ten sprays in any one crop, it also means that growers have 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 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 low levels of foliar blight do not necessarily mean that there is a reduced risk of tuber blight. Trials have shown that where there were low levels of foliar blight at the end of the season, there can be a risk of high levels of tuber blight. (BPC trials 2003-2005). 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," concludes Andy.
