Stress factors add to Alternaria risk


14 June 2022
'Stress factors set to hit potato crops over the coming weeks could increase the risk of Alternaria (early blight) outbreaks.'

MANY crops are still suffering the adverse effects of exceptionally low rainfall this spring, while the hugely inflated cost of fertiliser has seen potato growers cut back nutritional inputs to the bare minimum, according to Syngenta Technical Manager, Andy Cunningham. 

“Any agronomic factor that increases stress on the crop can act as a precursor for Alternaria infection, as well as the severity of the outbreak,” he said. “Early season infection and subsequent loss of leaf area inevitably has a greater impact on yield.” 

With the onset of stress effects, Andy believes growers should look to consider Alternaria protection earlier in their blight programme, as fungicide control of the pathogen must be applied preventatively.

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“Alternaria treatments have historically been focussed to start around the end of June or beginning of July,” he said. “Where growers have identified an increased risk of stress, or have historically suffered from Alternaria losses, however, that may need to be brought forward this season.”

Recent Alternaria research in Denmark, has suggested that while all cultivars in the trials were susceptible to Alternaria, the rate at which the infection developed in the foliage could indicate some varietal resistance. Later maturing varieties were typically, but not exclusively, more resistant to disease spread.

Successive seasons reporting of UK Alternaria monitoring by NIAB, sponsored by Syngenta, has highlighted no significant varietal trends. It has, however, repeatedly shown that A. alternata has been the first early blight pathogen to hit potato crops, followed by later infections of A. solani.

More details are included in the July issue of Potato Review. If you would like to subscribe, click here.

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