The Department of Conservation plans to spend $12 million this year on rodent control with 1080 poison as it fights a "mega'' beech mast fruiting season.

Doc Western South Island director Mark Davies said priority sites included Abbey Rocks, near Paringa, Arawhata-Waipara, Haast kiwi sanctuary, Landsborough Valley, New Creek (between the Buller and Mokihinui rivers), Okarito, Punakaiki, Te Maruia and the western part of Kahurangi National Park.

Planning was advanced but operations would proceed only if rodent threshold levels were reached, Davies said.

The total area proposed for predator control was 500,000ha, including aerial and ground control operations.

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"We can't yet give an overall cost for the West Coast programme for 2019 but if all operations go ahead it's likely to be about $12 million,'' he said.

"This includes monitoring of pests before and after control, as well as the outcomes from this work for the native species we are protecting.''

Aerial operations are being planned over the coming winter and spring and the first non-toxic prefeed is likely to occur in May, subject to results of rodent monitoring.

"We are expecting a large scale or 'mega' beech mast [seeding] this year, as predicted by climate models and evidenced by widespread flowering in beech forests last spring.''

Doc was assessing the size of the beech and rimu mast through its seed sampling programme.

Forest seeding results in rapid increases in rodent populations, which in turn fuels a spike in stoat numbers.

Ospri has one 1080 poison drop advertised on its website for this winter, covering about 40,390ha starting near Reefton and reaching almost to Lyell.