Spider mite on cucumber leaves in a greenhouse: what should be done? - briefly
Inspect cucumber foliage frequently, discard severely infested leaves, and raise greenhouse humidity to 60‑70 % to suppress mite reproduction. Apply a cucumber‑compatible miticide or introduce predatory mites (e.g., Phytoseiulus persimilis) following label instructions.
Spider mite on cucumber leaves in a greenhouse: what should be done? - in detail
Spider mites frequently colonize cucumber foliage in greenhouse environments, especially under low‑humidity, high‑temperature conditions. Adult females are less than 0.5 mm long, translucent to reddish, and lay eggs on the underside of leaves. Juvenile stages feed by piercing epidermal cells, extracting sap, and leaving stippled, yellow‑bronzed lesions that coalesce into bronzed patches. Heavy feeding reduces photosynthetic capacity, weakens plants, and predisposes them to secondary pathogens.
Effective management begins with early detection. Inspect the undersides of leaves twice weekly using a 10× hand lens. Look for tiny moving specks, webbing, and the characteristic speckled damage. Sticky traps placed at canopy level can capture dispersing motile stages, providing a quantitative indicator of population buildup.
Cultural measures reduce mite proliferation:
- Maintain relative humidity above 60 % during the day; low humidity favors mite reproduction.
- Keep temperatures within the optimal cucumber range (18‑24 °C) and avoid prolonged periods above 30 °C.
- Provide adequate air circulation with oscillating fans to disrupt mite movement.
- Remove and destroy heavily infested leaves or entire plants to eliminate sources of inoculum.
- Rotate crops with non‑host species (e.g., lettuce) for at least one growth cycle to break the mite life cycle.
Biological control offers sustainable suppression. Introduce predatory mites such as Phytoseiulus persimilis, Neoseiulus californicus, or Amblyseius swirskii at a rate of 5–10 predators per square meter. Ensure the greenhouse environment supports their activity by maintaining moderate humidity and avoiding broad‑spectrum insecticides that would harm the predators. Supplementary releases may be required every 7–10 days until the pest population falls below economic thresholds (typically 5–10 mites per leaf).
If chemical intervention becomes necessary, select products with proven efficacy against Tetranychidae and low residual activity. Recommended options include:
- Abamectin – apply at 0.02 % (w/v) spray, repeat after 7 days if needed.
- Spiromesifen – 0.025 % (v/v) foliar spray, re‑treat after 10 days.
- Neem oil – 2 % (v/v) formulation, repeat every 5–7 days.
Rotate active ingredients to delay resistance development. Observe pre‑harvest intervals and maximum residue limits for cucumber.
Integrated pest management (IPM) combines the above tactics. Set an action threshold (e.g., 5 motile mites per leaf) and initiate biological control first; supplement with targeted miticides only when the threshold is exceeded despite predator presence. Record monitoring data, environmental conditions, and treatment outcomes to refine future decisions.