Important to maintain protection against tuber blight right through until harvest

UK - August 02, 2007

This year has been a very difficult season so far for potato growers, with very high blight pressure in the UK and across Europe, difficult weather conditions, limited spray opportunities and some blight products in tight supply.  Consequently good quality potatoes will be hard to achieve and growers must keep their spray intervals tight and continue to use fungicide treatments with tuber blight protection right through to harvest, according to Dow AgroSciences.

"With the many difficulties facing potato growers this year, they are looking for blight fungicides that can be used to protect the crop from now on right through until harvest and products that are flexible to use.  Electis has approval for up to ten applications per season, one hour rainfastness, excellent blight protection, proven zoospore activity, compatibility with desiccants and a 7 day harvest interval, offering this important flexibility.  If kickback is needed, some cymoxanil should be added to Electis," says Andy Leader, Principal Biologist for Dow AgroSciences.

"Potato foliage and stems can act as important sources of zoospores, which drop off or are washed off into the soil through which the tubers are lifted.  An effective blight programme must prevent foliar blight and additionally prevent zoospores from being produced throughout stable canopy and senescence phases, so that the risk of blight is covered."

"Whilst the optimum timing to maximize the effect of Electis on zoospores is early stable canopy, it is a useful component in any programme used in conjunction with other zoospore-active fungicides," advises Andy.

"It is not always the crop with most obvious foliar blight that has the highest tuber blight.  Past experience shows that fields with seemingly low foliar blight can produce sufficient spores to cause significant levels of tuber blight.  Very little inoculum on the foliage is needed for spores to be washed down into the soil and infect tubers.  So every effort must be made to keep disease out of the crop.  The choice of fungicides from mid season programmes onwards makes a significant difference in reducing tuber blight and improving the quality of the end sample.  Growers should use products with known, proven zoospore activity which can be mixed with desiccants so that the crop is kept clean to the end and tuber quality and yields are protected," adds Andy.

"Zoxium in Electis stops the formation and release of zoospores.  When used in a suitable programme designed to keep out blight, it can be tank mixed with diquat, glufosinate-ammonium and carfentrazone-based desiccants, protecting the crop through to lifting.  The only desiccant that does not need to be mixed with a fungicide is acid, as it has the ability to kill blight spores itself."

Desiccating potatoes whilst maintaining tuber blight protection right through to the end of the harvest has become more complicated with the trend towards split dose desiccation treatments.

"This means using the first desiccant to open up the canopy and the second one to desiccate the crop more thoroughly.  Using split treatments can mean that the crop is exposed to blight infection for a longer period of time and could increase the risk of tuber blight overall.  Whatever haulm destruction method is preferred, it is essential to maintain effective protection against tuber blight right up to the time the haulm has died and lifting has started, especially this year when the risk of tuber blight is so high," says Andy.

Maintaining quality this year will be more important than ever with crops under water in some parts of the UK and blight outbreaks across Europe reducing supply to the market, concludes Andy.