Growers to treat all types of blight

Potato growers should keep spray intervals tight and use robust fungicide treatments with both foliar and tuber blight protection, experts at Dow AgroSciences have said.

They added that, although blight pressure is not as severe as it was last year, it remains consistently high - as indicated by a run of Smith Periods (when temperature and humidity values are conducive to blight) throughout the early and mid-season.

Dow AgroSciences principal biologist Andy Leader said that both tuber and foliar applications are needed as the two are linked.

"Zoospores - produced on foliage and stems - are the causal agents of tuber blight and these motile spores are produced when temperatures get below 15 degsC. These zoospores then drop off or are washed off into the soil through which tubers are lifted.

"But it is not always the crop with the most obvious foliar blight that has the highest 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 from tuber initiation onwards."

He pointed out that an effective blight programme aims to protect against foliar blight and prevent zoospores from being produced. "Not all fungicides have proven activity on zoospores. Zoxium in the protectant fungicide Electis stops their formation and release. Other fungicides act on zoospores once they are released.

"Considering the different modes of action on zoospores, it is advisable to use Electis early on in the programme from stable canopy or tuber initiation onwards, so reducing the initial zoospore population. By reducing the zoospore loading as early as possible after tuber initiation, this will optimise the activity of fungicides with direct zoospore activity," he said.

Leader said that fungicide choice from mid-season programmes onwards "makes a significant difference in reducing tuber blight and improving the quality of the end sample".

He added: "Growers should use products with 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.

"The protectant fungicide Electis has approval for up to 10 applications per season, no restrictions on applications in blocks or sequences, one hour rainfastness, proven zoospore activity, compatibility with desiccants and a seven-day harvest interval.

"If kickback is needed, as was the case in the majority of situations last year, cymoxanil should be added to Electis."


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