Late blight in potatoesrequires a full protective programme, starting at the rosette stage and runningright through to harvest. UK growers have a wide choice of effective fungicidesand need to put together the right programme using the right products at theright time, according to Gowan Comrcio.
Technical Manager RobertPlaice says that applying fungicides in a proactive and flexible way is the keyto success, especially with the more virulent blight strains we have totackle. Unlike other Europeancountries, the UK blight population is dominated by two particularly aggressivestrains – 6_A1 and 13_A2. These strains are characterised by their ability tothrive at lower temperatures and to produce more spores through shorter lifecycles. At most stages in the blight life cycle, fungicides should be deployedin a protective manner in order to stop infection.
Studying the detailedactivity of fungicides, we know that both active ingredients in Electis, zoxiumand mancozeb, have specific properties on spores. Mancozeb prevents sporegermination on the leaf surface and zoxium acts on cell division of the fungus,preventing formation of the next nucleus and so stopping germ tube elongationof spores and preventing infection. It does this as the germ tube grows alongthe leaf surface or down through the waxy leaf cuticle into the leaf. Thisanti-sporulant activity is in addition to zoxiums unique effect on zoosporeproduction and motility, which is needed to prevent against tuber blight,explains Rob.
It is important to drilldown into the intricacies of how fungicides work so that they are positioncorrectly within the normal ten to twelve fungicide sprays programme. Eachfungicide is different in the way it protects the plant, its activity on sporesand zoospores and its effects on early and late blight. Looking at Electis, itis best positioned in the second half of the spray programme, after full canopygrowth and before the last two sprays which are usually Shirlan (fluazinam) orRanman (cyazofamid).
Considering tuber blight, notall blight fungicides have proven zoospore activity and those that do can alsowork in different ways. Zoxium in Electis stops zoospores being formed and released, resulting in non-viablespores, incapable of infecting tubers.Its use reduces zoospore loading, so optimizing the activity of otherfungicides that work on motile zoospores.
Heexplains that fluazinam and cyazofamid act on motile zoosporesonce they are released, preventing them from reaching tubers. So these products are more beneficial andcomplement Electis when they are applied at the end of the programme.
Rob goes on to say that Electis is a robust and effective fungicidecontaining two complementary and effective active ingredients. It is extremely rainfast and has a stronganti-resistance position. There has been no reported resistance to mancozebafter more than 40 years of commercial use. Zoxium also works on a site withinthe nucleus of the fungal cell where very few other fungicides work, so it addsanother element of resistance management to the mix.