What's eating my marsh fern?

Marsh Fern (Thelypteris palustris) is a wetland native fern that is generally pest-free. Slugs may browse soft new growth in spring. The Marsh Fern Moth (Fagitana littera) is a notable host-specific caterpillar whose larvae feed on the fronds — it is the only known host of this uncommon moth. Overall foliar pests are rarely severe.

Irregular holes eaten in soft young fronds, most common in spring and in moist garden conditions that also suit this fern Apply iron phosphate pellets or Phasmarhabditis nematodes when soil is moist and above 5°C; clear debris around the colony; sharp grit mulch is less effective in wet bog garden conditions

Larvae chew ragged holes in frond pinnae through summer; Thelypteris palustris is the sole known larval host plant of this moth Hand-pick caterpillars; encourage birds to forage in the fern colony; apply Bt spray to fronds if populations are large enough to cause significant defoliation

Brown waxy bumps on stipes and rachis; heavy infestations weaken fronds and cause yellowing Scrub off manually with soapy water; apply horticultural oil spray; cut and dispose of heavily infested fronds to reduce the population