In a greenhouse, control pests and fungal disease mainly by airflow and cleanliness: ventilate, space plants for air movement, avoid overhead watering, and cover vents with fine mesh. Add ladybugs and lacewings against aphids, yellow sticky traps for whitefly, and copper or beer traps for slugs.
Greenhouse pest management is the set of habits that keeps insects, slugs and fungal disease from building up in a warm, humid, sheltered space.
The Same Warmth That Grows Plants Grows Their Enemies
A greenhouse is a protected, warm, often humid space with a steady food supply, which suits pests and fungus as much as it suits crops. There is no weather to knock the numbers back. The defense is mostly habit: look often, keep air moving, and act on small problems before they become large ones. Pest Control and Biological Control cover the wider field; this page is the greenhouse version.
What You Need
- Mesh fine enough to keep insects out of the vents
- Yellow boards and a sticky smear for traps — salvaged petroleum jelly works
- Diluted soap spray — it is compatible with Greywater Recycling
- Copper wire or strip for slug barriers, and shallow dishes for beer traps
- A hand lens, if you have one, for checking leaf undersides
Method: A Weekly Routine
Step 1: Inspect. Turn leaves over. Look for aphid clusters, whitefly clouds when you shake a plant, slime trails, and spots or mold.
Step 2: Aphids — encourage predators and spray. Encourage ladybugs and lacewings. Spray with diluted soap, covering the undersides of the leaves. Soap kills soft-bodied insects on contact, so it needs repeating.
Step 3: Whitefly — trap. Smear yellow-painted boards with salvaged petroleum jelly and hang them among the plants. The insects are drawn to the yellow and stick.
Step 4: Fungal disease — change the air. Improve ventilation, avoid watering overhead so leaves stay dry, and space the plants so air passes between them. Remove infected leaves and carry them out of the house.
Step 5: Slugs — barrier and trap. A strip of copper wire around raised beds is a barrier, and a beer trap sunk to the rim of a dish draws slugs in.
Step 6: Screen the vents. Fine mesh over vents keeps insects from entering while allowing airflow. Mesh reduces the free opening, so enlarge vents to compensate; see Ventilation & Overheating Prevention.
Common Mistakes
- Watering over the leaves in the evening — wet leaves overnight invite fungus.
- Dense planting — still air and crowded leaves are ideal for mildew.
- Leaving diseased leaves in the house — spores spread from the debris.
- Mesh without bigger vents — the house overheats.
Safety
Sprays and spores
Soap spray is mild but irritates eyes; wear eye protection. Moldy plant debris can irritate lungs; wear a cloth mask when clearing heavy mold and carry it out damp rather than shaking it.
What’s Next
- Learn next: Pest Control — the wider toolbox
- Combine with: Companion Planting — plant pairings that deter some pests