Throughout the North Island, regions are being hit hard by animal facial eczema at the moment, and while the problem is not too bad in Central Hawke's Bay as a whole, there are hot spots where spore counts are soaring.
Vet Services Hawke's Bay conducts weekly monitoring at selected properties across the district, and in some cases spore levels are at extremely toxic levels.
Vet Services managing director Richard Hilson said warm weather in March, including overnight temperatures of at least 12C, which preceded some rainfall created good conditions for the fungus to grow.
Over the last week phone calls have been coming in from concerned farmers.
"One day last week between two of us we fielded 14 calls by lunchtime. By the time it's a problem though, it's too late."
At least one farmer they had spoken to recently had 10 per cent of their mixed age ewes affected and another had the disease among half of their lambs.
Facial eczema affects sheep, cattle and deer, but lambs and sheep are usually the canary in the coalmine, falling victim first if it's around.
"Lots of people ring us but they could be monitoring it themselves - it's easy and cheap at $22 a sample. If you have even got half a concern start monitoring before it's too late," Mr Hilson said.
Vet Services monitors about 11 farms throughout CHB with some properties recording paddocks with more than 300,000 spores per gram of pasture in the last week of March. Others, however, were as low as 20,000.
Farmers who monitor stock themselves will often check paddock by paddock to see where to move animals to next, said Mr Hilson.
As well as this preventative measure, treating stock with zinc oxide is an option - a weekly drench for sheep or daily treatment for dairy cows.
"It helps the animals avoid the issues, but is not a total preventative."
Once the animals have the disease, symptoms start with their ears becoming inflamed and droopy, and then, in the case of sheep, they begin losing their wool, their skin gets scabby, and liver damage can ensue. The symptoms are similar in other animals, and can also affect productivity.
If caught before it gets too bad the symptoms can be eased by keeping the animals in shade for a few days after which they tend to come right.
"A couple of people are treating their animals by keeping them in the woolshed during the day - no matter what the liver damage is, the most important thing is that they get no sunshine on them," Mr Hilson said.
Liver damage is not such an issue if the animals are young, but if they are pregnant the stress can cause them to lose condition.
Another prevention alternative was to buy rams from farmers using the long-term Ramguard programme, where sires were innoculated with the sporedesmin toxin.