The risk of facial eczema is high throughout most of the North Island.
The rainfall which brought relief to dry parts of the North Island last week has caused a sharp spike in toxic spores in pasture which cause facial eczema.
The livestock disease can cause severe liver damage for animals who catch it.
Asure Quality's Facial Eczema Monitoring Co-ordinator Leo Cooney said most regions in the North Island have a moderate to high risk number of recorded toxic spores.
"Counts coming in from Northland vary between 15 to 140,000 spores per gram, Waikato 20,000, 480,000 in the Hamilton area.
"The East Coast, quite a jump there, 80,000 to 750,000 spore per gram and in the lower North Island we're getting counts between 30,000 and 240, 000 spores per gram, so farmers and lifestyle block owners in these areas, that have had a history of facial eczema should be taking full precautions."
Mr Cooney said spore counts in Rotorua are high, at 225,000, but levels in the Bay of Plenty and Whakatane regions are not as high risk.
And he said the high levels were not likely to drop significantly any time soon.
"It could be a big programme for quite a while because we're into an unusual weather pattern and we're back into what almost seems like equinoctial sort of weather, very changeable, very windy and very unsettled, there will be a little bit of respite from all the wind we're getting but it's fairly short lived and I think that the spore counts are telling us that it's dangerous so we shouldn't relax and think that."