How to Identify Fungus Gnats on Plumeria (Adults, Larvae & Root Damage)

Fungus gnats are small flying pests that often appear around potted plumeria or propagation trays. While the adults are mostly harmless, their larvae feed on organic matter and delicate roots in the soil, posing a real threat to seedlings and newly rooted cuttings. If you’re seeing tiny black flies hovering near the soil or if your cuttings are wilting unexpectedly, fungus gnats could be the cause.

This guide will help you recognize the early signs of fungus gnat activity, understand where to look, and take the first steps to protect your plumeria’s root health.

What Are Fungus Gnats?

Fungus gnats (Sciaridae family) are small, mosquito-like insects often mistaken for fruit flies. They are:

• Black or dark gray
• 1.5–3 mm in length
• Weak flyers, often seen walking or hovering near the soil
• Attracted to moist, organic-rich soil, especially in propagation zones

Life Cycle:

• Adults live ~1 week and lay 100–200 eggs in damp soil
• Larvae hatch and feed on fungi, decaying matter, and fine roots
• Complete life cycle: 3–4 weeks (shorter in warm, humid conditions)

Why Fungus Gnats Are a Problem for Plumeria

While adult gnats don’t feed on plants, their larvae feed on root hairs, which can lead to:

• Root damage in seedlings and cuttings
• Poor rooting success or stem rot in propagation
• Wilting, yellowing, or slow growth despite ideal conditions
• Increased risk of damping-off disease (fungal infection in seedlings)

Where and When to Look

Fungus gnats favor:

• Propagation trays, rooting containers, and seedling flats
• Peat-heavy or compost-rich soil mixes
• Cool, moist areas with organic buildup

Look for:

• Adult gnats flying near the soil line or under grow lights
• Larvae (white, legless, with black heads) in the top inch of soil
• Shiny slime or greenish mold on the soil surface
• Sudden seedling collapse or cutting failure in damp mix

Visual Signs of Fungus Gnat Activity

1. Adult Gnats Flying Around Soil

• Appear in clouds when pots are disturbed
• Found hovering near seedlings or moisture trays
• Easily trapped on yellow sticky cards

2. Root Damage Symptoms

• Seedlings wilt or “damp off” with brown bases
• Cuttings stall or rot at the soil line
• Leaves turn pale or growth slows despite good light and nutrients

3. Visible Larvae

• Found in freshly watered pots or after disturbing the top inch of soil
• White, semi-transparent worms with black heads, ~4–5 mm long
• May be visible at drainage holes in extreme cases

Fungus Gnats vs. Similar Issues

Tools for Detection

• Yellow sticky traps: Place near soil to catch adult gnats
• White paper test: Tap pot and see if black gnats appear
• Soil drench and flush: Use a mild peroxide solution to force larvae to surface
• Magnifying lens: Examine soil for tiny white larvae near the top inch

When Fungus Gnats Are Most Active

• Year-round indoors
• Spring through fall in warm, humid weather
• After overwatering, poor drainage, or buildup of organic matter
• In propagation domes or greenhouse trays where moisture is retained

Conclusion

Fungus gnats may seem like a minor nuisance, but their larvae can silently damage young plumeria roots and sabotage propagation success. Spotting tiny flying gnats, slimy soil, or unexplained wilt is the first step. Once identified, fungus gnats are very treatable—and in the next article, we’ll walk through exactly how to control them using organic, biological, and chemical methods.