Late blight in potatoes requires a full protective programme, starting at the rosette stage and running right through to harvest. UK growers have a wide choice of effective fungicides and need to put together the right programme using the right products at the right time, according to Gowan Comércio. Technical Manager Robert Plaice says that applying fungicides in a proactive and flexible way is the key to success, especially with the more virulent blight strains we have to tackle.
“Unlike other European countries, the UK blight population is dominated by two particularly aggressive strains – 6_A1 and 13_A2. These strains are characterised by their ability to thrive at lower temperatures and to produce more spores through shorter life cycles. At most stages in the blight life cycle, fungicides should be deployed in a protective manner in order to stop infection.”
“Studying the detailed activity of fungicides, we know that both active ingredients in Electis, zoxium and mancozeb, have specific properties on spores. Mancozeb prevents spore germination on the leaf surface and zoxium acts on cell division of the fungus, preventing formation of the next nucleus and so stopping germ tube elongation of spores and preventing infection. It does this as the germ tube grows along the leaf surface or down through the waxy leaf cuticle into the leaf. This anti-sporulant activity is in addition to zoxium’s unique effect on zoospore production and motility, which is needed to prevent against tuber blight,” explains Rob.
“It is important to drill down into the intricacies of how fungicides work so that they are positioned correctly within the normal ten to twelve fungicide sprays programme. Each fungicide is different in the way it protects the plant, its activity on spores and zoospores and its effects on early and late blight. Looking at Electis, it is best positioned in the second half of the spray programme, after full canopy growth and before the last two sprays which are usually Shirlan (fluazinam) or Ranman (cyazofamid).”
“Considering tuber blight, not all blight fungicides have proven zoospore activity and those that do can also work in different ways. Zoxium in Electis stops zoospores being formed and released, resulting in non-viable spores, incapable of infecting tubers. Its use reduces zoospore loading, so optimizing the activity of other fungicides that work on motile zoospores.”
He explains that fluazinam and cyazofamid act on motile zoospores once they are released, preventing them from reaching tubers. “So these products are more beneficial and complement Electis when they are applied at the end of the programme.”
Rob goes on to say that Electis is a robust and effective fungicide containing two complementary and effective active ingredients. “It is extremely rainfast and has a strong anti-resistance position. There has been no reported resistance to mancozeb after more than 40 years of commercial use. Zoxium also works on a site within the nucleus of the fungal cell where very few other fungicides work, so it adds another element of resistance management to the mix.”
Electis contains 8.3% w/w zoxium (zoxamide) and 66.7% w/w mancozeb, formulated as a WDG. It is recommended on all varieties of potatoes at spray intervals of 7 to 10 days. It has a dose rate of 1.8 kg/ha in 150-600 litres of water per hectare. It has a maximum number of treatments of 8 per crop and a harvest interval of 7 days. It is packed in a 3-ha pack (5.4 kg).
For further information, please contact Robert Plaice, UK and Ireland Technical Manager for Gowan on 07747 567227.