How to combat spider mites in a greenhouse on tomatoes? - briefly
Implement regular scouting, introduce predatory mites, and apply horticultural oil or sulfur sprays when populations exceed threshold; maintain low humidity and adequate ventilation to suppress spider mite reproduction.
How to combat spider mites in a greenhouse on tomatoes? - in detail
Spider mites thrive in warm, dry greenhouse conditions and can quickly defoliate tomato plants. Early detection and a layered management plan are essential for maintaining healthy crops.
Inspect foliage daily for the following signs: tiny moving specks on the underside of leaves, fine webbing, stippled or yellowed leaf tissue, and a gradual reduction in plant vigor. Use a white sheet of paper held beneath leaves; disturbed mites will scatter, confirming their presence.
Implement cultural practices that reduce mite populations:
- Maintain relative humidity at 60‑70 %; higher humidity disrupts mite development.
- Keep temperatures between 18‑24 °C; avoid prolonged periods above 30 °C.
- Space plants to allow good air circulation; use fans or ventilation to prevent stagnant air.
- Remove and destroy infested leaves or whole plants promptly.
- Rotate crops annually and avoid planting solanaceous crops in the same location for more than two seasons.
Introduce biological agents as the primary control method:
- Release predatory mites (e.g., Phytoseiulus persimilis, Neoseiulus californicus) at a rate of 10‑20 predators per plant when mite numbers exceed 5 mites per leaf.
- Apply entomopathogenic fungi such as Beauveria bassiana according to label rates; repeat applications every 7‑10 days during humid conditions.
- Encourage natural enemies by providing refuge plants and avoiding broad‑spectrum insecticides.
When biological options are insufficient, use selective acaricides:
- Apply neem oil or horticultural oil at 1‑2 % concentration, covering both leaf surfaces; repeat every 5‑7 days.
- Use sulfur‑based products (e.g., potassium bisulfate) at 2 % solution; limit to three applications per month to prevent phytotoxicity.
- Reserve synthetic miticides (e.g., abamectin, spirodiclofen) for severe outbreaks; rotate modes of action to delay resistance.
Integrate resistance management:
- Alternate chemical classes every application.
- Combine chemical treatments with biological releases, ensuring a 24‑hour interval to avoid harming predators.
- Monitor mite populations after each intervention; adjust tactics based on efficacy.
Maintain sanitation and record‑keeping:
- Clean greenhouse benches, benches, and equipment regularly.
- Record temperature, humidity, mite counts, and control measures in a logbook.
- Review data weekly to identify trends and refine the program.
By combining vigilant scouting, environmental regulation, biological agents, and judicious chemical use, growers can suppress spider mite infestations on greenhouse tomatoes and protect yield quality.