Pest identification
What's eating my watercress fern?
Spider mites
Signs: Tiny pale dots and fine webbing on the upper surface of narrow fronds; fronds bronze and shrivel.
Control: Increase humidity with a pebble tray or humidifier, wash fronds under lukewarm water, and spray insecticidal soap every 5 days for three cycles.
Fungus gnats
Signs: Larvae chew fine roots, causing wilting and slow growth; adults are tiny black flies around the soil surface.
Control: Allow the top inch of compost to dry between waterings; use yellow sticky traps for adults and a Bacillus thuringiensis var. israelensis (Bti) drench for larvae.
Scale insects
Signs: Small waxy bumps on frond stalks and midribs; fronds yellow and shed early.
Control: Scrape off with a soft brush and treat with neem oil or insecticidal soap; repeat weekly for a month.
Keep watercress fern pest-free
Healthy plants resist pests best. Get the basics right:
Watercress Fern pests — FAQ
What is eating my watercress fern?
Watercress Fern (Blechnum penna-marina) is a compact ground fern prone to spider mites in low humidity, and to fungus gnats when the substrate stays waterlogged. Scale and mealybugs are occasional visitors. Good air circulation and careful watering prevent most indoor pest problems.
How do I get rid of spider mites on watercress fern?
Tiny pale dots and fine webbing on the upper surface of narrow fronds; fronds bronze and shrivel. Increase humidity with a pebble tray or humidifier, wash fronds under lukewarm water, and spray insecticidal soap every 5 days for three cycles.
How do I get rid of fungus gnats on watercress fern?
Larvae chew fine roots, causing wilting and slow growth; adults are tiny black flies around the soil surface. Allow the top inch of compost to dry between waterings; use yellow sticky traps for adults and a Bacillus thuringiensis var. israelensis (Bti) drench for larvae.
How do I get rid of scale insects on watercress fern?
Small waxy bumps on frond stalks and midribs; fronds yellow and shed early. Scrape off with a soft brush and treat with neem oil or insecticidal soap; repeat weekly for a month.