Keep your foot on the pedal in the race against potato blight

UK - July 08, 2005

As blight pressure mounts across the country, Dow AgroSciences is advising potato growers to keep their foot on the pedal with regard to potato blight protection and to keep their crop well protected through the use of an effective blight fungicides, such as Electis, applied at tight spray intervals.

"A few weeks ago we were concerned about dry conditions, one week later it was wet conditions.  A typical British summer!  But growers need to be aware that the weather that we experience should have only minor impact on the strategy for effective potato blight prevention when the crop is at full canopy.  This is because the potato blight organism (Phytophthora infestans) produces sporangia on infected leaves and stems in great numbers when the conditions are warm, at around 25°C and humid.  These spores move either in free water or in the air and spread the disease long distances.  In practical terms, it is the condition within the canopy or the microclimate, rather than macroclimate, that will be pertinent.  Also with irrigation, the humidity within the canopy that is closed will be high.  A strong protectant such as Electis, based on zoxium and mancozeb, is an appropriate product to use from now on.  It is also important that whatever fungicide regime you are using, that the protectant pressure is kept up and that the spray intervals are kept tight.  Electis can be used at seven-day intervals. You have too much to lose to take your foot off the pedal now," comments Andy Leader, Principal Biologist for Dow AgroSciences.

"As the season progresses and temperatures lower, these cooler conditions are sub-optimal for the spread of foliar blight, but are optimal for tuber blight.  This is because tuber infections are caused by another type of spore, a zoospore that is produced at lower temperatures of between 10-15°C.  They fall or are washed down into the soil by rainsplash from foliar and stem infections.  These twin-tailed motile zoospores swim in the soil water towards the tubers and infect them by germinating near to and entering at buds, lenticels and wounds, which provide easy access points.  The choice of blight fungicide at this point in the programme can make a critical difference to the successful prevention of tuber blight.  You need to choose a product that has good activity on zoospores.  Electis has been shown to adversely affect zoospore release, resulting in the production of non-motile spores, which are incapable of infecting tubers.  When used repeatedly in a suitable programme prior to the initial production of zoospores, Electis protects against both foliar and tuber blight," says Mr Leader.

Electis contains 8.3% w/w zoxium and 66.7% w/w mancozeb, formulated as a WDG.  It is recommended on all varieties of potatoes at spray intervals of 7 to 14 days.  It has a dose rate of 1.8 kg/ha in 200-600 litres of water per hectare.  It has a maximum number of treatments of 10 per crop and a harvest interval of 7 days.  It is packed in a 3-hectare pack (5.4 kg).