What's eating my cystopteris fragilis?

Cystopteris fragilis (brittle bladder fern) is generally low-maintenance outdoors, but slugs and snails are the primary threat, rasping tender new fronds in spring. Vine weevil grubs can damage roots, and caterpillars occasionally notch frond edges. Deer and rabbits may browse young growth in woodland gardens.

Ragged, irregular holes in young fronds and croziers; slime trails visible in the morning Apply iron phosphate pellets around crowns at night; use copper tape on containers; encourage ground beetles by reducing mulch depth

Notched leaf margins from adult beetles; sudden wilting and plant collapse from grubs eating roots Apply nematodes (Steinernema kraussei) to moist soil in late summer or early autumn; use imidacloprid drench in severe cases

Clean notches or holes chewed from frond margins and tips Hand-pick caterpillars; apply Bacillus thuringiensis (Bt) spray to foliage if infestations are heavy