POTATO growers should now be on the look out for potential stress factors on crops caused by alternaria, before the increasingly prevalent pathogen hits.

With blight pressure running high this season as a result of wet, mild weather, growers should aim to combine the best foliar blight control active, with the highest possible level of alternaria protection.

That means applying Amphore Plus, according to Syngenta's field technical manager, Douglas Dyas, who warned that there is a high proportion of commonly-grown varieties susceptible to the disease. However, he pointed out, NIAB leaf testing last season highlighted that all varieties could be infected, especially when under stress.

NIAB tests last year revealed 20 of the 57 samples collected contained the aggressive a solani, a specific pathogen of potatoes and solanaceae plants, along with 30 infected with an earlier hitting, but less damaging sub species.

Agronomists agree that alternaria is increasing in the UK for a number of reasons – more susceptible varieties; changeable weather; a reduction in the use of mancozeb in blight programmes; and shorter rotations.

Mr Dyas added: “Anything that puts stress on the potato plant will increase the risk of Alternaria attack. The earlier that it hits the greater the potential loss of yield, and the greater the chance of a solani affecting tuber quality for storage.

“Alternaria leaf spots typically appear from the end of June, into July,” reported Mr Dyas. “It is usually followed by the highly pathogenetic a solani from mid-July onwards – which can decimate whole fields within days of initial infection.

“An early start to the Amphore Plus programme has proven to be most effective in preventing infection and stopping early crop loss,” he said.

It contains the full dose of the industry-leading single-active blight fungicide, Revus, in combination with a key alternaria active, difenoconazole. “Crucially, the pre-mixed formulation contains 20% more active per ha than the maximum permitted for growers to tank-mix as straights," he said.

“The one-can solution is quick and easy to use when spray operators are under immense pressure to maintain blight application intervals during the catchy weather conditions,” he added.