JUST a handful of grapes, onions or macadamia nuts can make dogs very sick, even kill them, says the author of a new 976-page guide to Australia's poisonous plants.

A few lily petals can have the same effect on a cat, and caged birds such as parrots can be felled by a few pecks of avocado flesh.

And don't even get Dr Ross McKenzie, the veterinarian toxicologist who wrote the guide and uncovered many of the surprising poisons, started on the dogs (and one cat) poisoned by eating marijuana and the cocker spaniel killed after eating a 250-gram box of cocoa.

''Some people regard pets as little humans. And they're not … They think, 'If it is good for me, it must be good for my pet', and that's not necessarily true,'' he said.

While these plants made pets sick, Dr McKenzie said the bigger issue was poisonous plants that cost farmers millions in lost livestock and veterinary treatment each year.

One of the most poisonous was the Cooktown ironwood, a native tree that grows in tropical areas. Even a small handful was quite capable of ''rolling over a large animal like a bull in half an hour'', Dr McKenzie said.

Another, he said, was lantana. Most Australians knew it was a weed but not many knew it poisoned and killed cattle, at huge cost.

In southern Australia, weeds such as Paterson's curse and common heliotrope caused cattle to suffer liver failure, the damage building up over several years until they eventually died.

''Toxic Ross'', as his students affectionately call Dr McKenzie, said new poisons were still being discovered, although the pace was slowing.

When it came to the average suburban family, Dr McKenzie said families with toddlers (who tended to put things in their mouths) should keep children away from flowering oleanders (poisonous to humans and cattle), foxgloves and the berries on the fragrant Lily of the Valley.

Australia's Poisonous Plants, Fungi and Cyanobacteria, published by CSIRO, is available at www.publish.csiro.au/pid/6507.htm