Farmers in the North Island and top of the South Island have been warned to be on look out for the livestock disease facial eczema, as hot weather dries off pasture.
At the start of its annual summer monitoring the AsureQuality agency has found high spore counts in the Rodney district, north of Auckland, in southern Waikato and Wairarapa .
Moderate spore counts have also been found at Wairoa and in the Horowhenua district.
The disease is spread by fungal spores in the litter of dead pasture.
Infected livestock suffer liver and skin damage which in severe cases can kill the animals.
Preventive measures include treating livestock with zinc oxide, and spraying pasture with fungicide.
AsureQuality manager Wayne Baxter said conditions are ripe for an explosion of spore levels.
Mr Baxter says facial eczema costs New Zealand farmers up to $100 million annually in production losses.
Farmers can check the AsureQuality, Meat and Wool and RD1 websites for updated regional spore counts.