Protecting Plumeria Seedlings from Fungus Gnats

Fungus gnats are small, mosquito-like flies whose larvae live in moist soil and feed on organic matter and roots. In plumeria seedlings, larval feeding damages root hairs, leading to reduced water and nutrient uptake, seedling stress, and increased vulnerability to diseases.

Identification and Life Cycle

• Adults are tiny black flies (1/8 inch) attracted to moist environments and decaying organic material.
• Females lay eggs in moist soil; larvae hatch within a few days.
• Larvae are slender, translucent worms with black heads, feeding on roots and organic debris for 2–3 weeks before pupating.

Damage Symptoms

• Seedlings exhibit poor growth, wilting, and yellowing despite adequate watering.
• Roots show feeding scars, reduced root hairs, and may be slimy or decayed.
• High larval densities can cause seedling death.

Environmental Factors

• Overwatering and poor drainage create ideal conditions.
• Organic-rich media favor larvae development.

Prevention Strategies

• Avoid overwatering; allow soil surface to dry slightly between waterings.
• Use sterile, well-draining seed-starting media.
• Remove plant debris and decaying matter from seedling areas.

Management and Control

Cultural Controls

• Improve drainage and airflow.
• Use sticky yellow traps to capture adults and monitor populations.

Biological Controls

• Apply Bacillus thuringiensis israelensis (Bti) as a soil drench targeting larvae.
• Introduce beneficial nematodes (Steinernema feltiae) that parasitize larvae.

Organic Treatments

• Use soil drenches with neem oil or insecticidal soap cautiously; avoid phytotoxicity.

Chemical Controls

• Reserve insecticides for severe infestations, using targeted products labeled for fungus gnats.