Fruit flies (mainly Drosophila spp.) are a significant problem during rainy and humid seasons, particularly in indoor microgreen units, where moisture, decomposition odours, and organic media attract them.

They do not damage the plant directly, but they:

Lay eggs in moist grow media

Encourage fungus growth and the larvae damage root hairs

Spread contamination

Reduce hygiene and shelf life

Create problems in food-grade microgreen production

1. Understand why fruit flies multiply in the rainy season

The rainy season creates ideal conditions for the growth of fruit flies. The conditions are:

High humidity (≥70%)

Stagnant moisture in trays

Wet cocopeat + decomposing roots

Slow drying of media

The fermentation smell attracts fruit flies

Poor ventilation in indoor setups

2. Immediate control measures (within 24 hours)

(A) Deep Cleaning & Media Hygiene

Remove all decomposed trays or spoiled microgreens.

Wash racks and trays with:

2% bleach solution (20 ml bleach per 1 L water) or

2% *Virex / any food-grade sanitizer.

Allow trays to sun-dry or air-dry completely.

(B) Reduce moisture

Do not overwater microgreens during monsoon.

Use fine mist spray instead of pouring water.

Keep exhaust fan or dehumidifier ON for 2–4 hours daily.

(C) Immediate fruit fly traps

Use a banana peel trap or an apple cider vinegar trap:

Vinegar Trap Recipe

3 tbsp apple cider vinegar

1 tbsp jaggery/sugar

3–4 drops of dish soap

Keep in small cups around the unit.

Traps reduce 70–80% adult flies in 2–3 days.

3. Medium-term control (3–7 days)

(A) Use neem oil spray (food safe)

Mix 5 ml neem oil + 1 L water + 2–3 drops mild soap

Spray on tray edges, floor, walls (not directly on microgreens).

Neem repels egg-laying females.

(B) Use Bacillus thuringiensis israelensis (BT-i) for larvae control

BT-i powder controls larvae in cocopeat.

Apply 1 g BT-i powder per litre of water

Water the trays lightly

Safe for microgreens.

(C) Cover trays with net or breathable lid

Use nylon mosquito nets to prevent egg-laying.

Helps in organic certification.

4. Long-term seasonal strategy (rainy season protocol)

(A) Indoor environment structure

Maintain Temperature: 22–28°C

Humidity: 50–60%

Use a dehumidifier or silica gel in racks.

(B) Airflow management

Install two-way ventilation:

Exhaust fan

Fresh-air inlet

Run fans for 1 hour in the morning + 1 hour evening.

(C) Strict waste management

Remove harvested stems immediately.

Keep waste in closed lids, not open bins.

Empty bins daily.

(D) Use beneficial predators

Safe for microgreens:

Hypoaspis miles (Stratiolaelaps) – eats larvae

Orius insidiosus – eats adult fruit flies

This is used in commercial setups.

5. Safe organic sprays for microgreen areas

6. What not to do in microgreen fruit fly control

·        Do not use chemical pesticides (not food safe)

·        Avoid stagnant water or over-misting

·        Do not keep fruits or vegetable waste near the rack

·        Avoid thick cocopeat layers (promotes larvae)

·        Don’t use heavy organic fertilizers indoors

7. Best practices for rainy season microgreen production

Use sterilized cocopeat

Use a thinner media layer (1.5–2 cm)

Avoid smelly organic matter (vermicompost, manure)

Ensure daily drying cycle

Use the UV lamp for 10–15 minutes after work hours

Maintain a clean-room style microgreen unit

Have a nice growth for your little microgreens…