The poisonous death cap is flourishing across Victoria ahead of the mushroom season this year.

Victorians are being warned not to pick wild mushrooms this autumn and winter because an abundance of toxic death caps are flourishing across the state.

Botanic Gardens Victoria scientist Dr Tom May says thunderstorms in December brought a "flush and a burst" of death caps ahead of the mushroom season in autumn and winter.

"This year we had good rain through summer so the soil's already charged up," Dr May told reporters on Thursday.

Death caps have a greenish-brown tinge on top but the toxic fungi can be distinguished from field mushrooms by their white underside.

"(Death caps) causes more fatalities worldwide than any other mushroom" Dr May told reporters on Thursday.

The abundance of death caps growing across Victoria prompted health authorities to issue a warning earlier than usual this year.

Victoria's Chief Health Officer Charles Guest said symptoms of death cap poisoning start with an upset stomach before the toxin attacks the liver, and death usually occurs within 48 hours.

"One mushroom can be fatal," Professor Guest said.

"Anyone who becomes ill after eating mushrooms should seek urgent medical advice and, if possible, take samples of the whole mushroom for identification."

The last recorded fatality from a death cap mushroom in Victoria was in 2012 when a woman visiting from China ate the fungi with relatives in Melbourne's east.

The poison in toxic mushrooms can't be cook out.

Health authorities also warned of the yellow staining mushroom, which is often mistaken for the field mushroom but is toxic and causes nausea, diarrhoea, vomiting and stomach cramps.

People are urged to buy their mushrooms from the supermarket rather than picking wild varieties.