New strains of potato blight could be pushing farmers' €4m annual spray bill even higher.
A new paper says that at least 27 species of blight, or 'Phytophthora' are now found across the country, with invasions on the rise in line with increasing globalisation and international trade in plants.
The increased threat to potatoes and other crops has resulted in higher bills for farmers, agricultural consultant Richard Hackett said.
"Potato blight now would be a more difficult beast to control than 15 years ago because there's more strains of it, and some are more difficult to eradicate," he said.
"Farmers have been using more fungicide. They're spending more than they did a few years ago because the strains are more difficult to control, and older, cheaper products are being withdrawn, often for good reason.
"As we've seen with potato blight, there's a number of strains of it. They can disappear and come back again another year. These strains can be very difficult to handle."
Potatoes are currently planted on some 8,000 hectares of land, mostly across Dublin, Meath and Louth. The cost of spraying with fungicides is some €500/ha, meaning the annual bill is €4m. Failure to spray can result in the loss of the entire crop.
The paper, Diversity and econoloy of Phytophthora species on the island of Ireland by Richard O'Hanlon, Alistair R McCracken and Louise R Cooke, was published in the Royal Irish Academy journal Biology and Environment. It says that the various strains can affect not just potatoes, but apples, raspberry plants, strawberries and trees.
It notes that at least 19 of the 27 species found here are not native in Europe.
"Several of the species have been detected in plants being traded internationally, highlighting the dangers of the trade in live plants for spreading invasive plant pathogens," the study says, adding there is "strong evidence" that international trade is contributing to the spread of Phytophthora.