After the second Tongariro eruption, farmers and rural residents have been advised to prepare in case an even larger eruption spreads high levels of ash.
Federated Farmers' warning has gone to members in Hawke's Bay, Waikato, Bay of Plenty, Rotorua-Taupo, Taranaki, Ruapehu, Tararua, Wanganui, Gisborne, Manawatu-Rangitikei, and Wairarapa.
"While the scale of the August 6 eruption had no practicable effect upon farm pasture, analysis of the ash produced showed moderate levels of soluble fluorine (F)," its notice to members said. "Should eruptions similar to 1995 and 1996 take place, the main effect on grazed pastoral systems is ash cover. Some livestock will be put-off grazing due to high levels of acidic and abrasive ash while others will continue to graze. If supplementary feed is unavailable, this may lead to starvation and if significant ash is ingested along with pasture, livestock are at risk from the disease, fluorosis.
"Experience from the 1995/1996 eruptions has shown that ash coverings of 2mm, low-grazed pastures and low rainfall following ash deposition are critical factors increasing hazard. Deaths of stock normally begin four-10 days after ashfall if no supplementary feed is available. Noting it is mid-spring, heavy or persistent rainfall quickly disperses such levels of ash and also rapidly leaches F; reducing the hazard considerably.
"In general, deer are likely to be the most susceptible to fluorosis, followed by cattle, with sheep being the most resistant. Fluoride is absorbed rapidly by grazing animals from ingested ash or contaminated water. In moderate levels of excess, it does not pass into milk."
Farmers are advised to maintain pasture length by regular rotation rather than close cropping - longer pastures are less likely to be completely covered.
If ashfall exceeds 2mm or coats more than 50 per cent of pasture/crops, they should move stock to less affected areas of the farm or supply supplementary feed. They should refill stock drinking troughs from bore or river supplies. If ash has not washed off pastures after two to three days, farmers should raise the quantity of supplementary feed and monitor stock condition closely.
Rural residents with roof-fed tank water supplies were advised to remove the roof connection to protect stored water.