Alternating mancozeb and the strobilurin fungicide Signum is providing the strongest alternaria control in a Frontier Agriculture trial.

But although this option added good alternaria activity, it would double the cost of a basic blight programme, said Reuben Morris, technical support manager from Frontier Agriculture.

Adding mancozeb to a base treatment of Revus (mandipropamid) and Ranman (cyazofamid) helped “considerably increase” alternaria control, he said.

But visual observations in the field showed this option was less effective against alternaria than when Signum (pyraclostrobin + boscalid) and mancozeb were alternated on top of the base blight programme.

Mr Morris said there had been little activity against alternaria from Revus and Ranman. “Those products are very good phytophthora blight products, but they’re not giving us any alternaria activity.”

Three blocks of Markies, a variety susceptible to alternaria, were planted in field trials at QV Foods. Blocks have been sprayed weekly since late May with the different treatments and observations recorded.