Any idea what could be effective? from a Google search all I am finding is "wide spectrum pesticide" which I wouldn't want to use.

Ferns are tasty. Many foods will make you sick if you eat enough of them. At a meeting of the Texas Gulf Coast Fern Society we had a program that included Fiddlehead casserole, Steamed fiddleheads, and fiddlehead salad. It was good fun. They are available on line, most commonly Bracken Fern Pteris aquilina. Vegetable fern, Diplazium esculentum, is very easy to grow and can take over your garden in no time. It makes a little tree fern and is great in salad.

Hi and Welcome Yes there is..... plant lots of native flowering trees, they will bring the birds who will in turn eat the caterpillars. Your Canna will come up again next season. If you cannot get rid of the caterpillars without chemical sprays pull them up and plants the rhizomes in pots for now.

That’s interesting .. I already have some spinosad but didn’t realise, it is marketed here as a fruit fly control, see the blurb below. Nature’s Way Fruit Fly Control has been included in this range because it’s based on spinosad, the naturally-derived insecticide found in Yates Success. Yates Nature’s Way Fruit Fly Control works by tricking the insect into absorbing the spinosad that’s been combined with an irresistible bait. After she emerges from her pupal case in the soil, the female fly looks to feed on a source of protein before she lays her eggs. When she eats the protein and sugar bait in Nature’s Way Fruit Fly Control, she also ingests a dose of the insecticide, which means she never makes it to the egg-laying stage. Fruit fly baits are nothing new but many have used a hormone that only attracts male flies (they’re the ones that don’t lay the eggs!) or have been based on a nasty chemical. Now Yates Nature’s Way Fruit Fly Control has a low toxic formulation that really works. also found this because spinosad is highly effective against diamondback moth, but because it also controls several other important lepidopteran pests such as heliothis (Helicoverpa spp.), cabbage white butterfly (Pieris rapae), cabbage centre grub (Hellula hydralis) and cabbage cluster caterpillar (Crocidolomia pavonana) at rates which provide growers with excellent value for money. Spinosad is highly active against loopers (Chrysodeixis spp.) and affords some control of cluster caterpillar (Spodoptera litura) and onion thrips (Thrips tabaci). So so if my rose slugs ever start on my buds I’ll use this. Might even do it on the climbing nahema as I can only squish so high! And they do shred the leaves to pieces ...