When should cucumbers be treated for spider mites in the greenhouse? - briefly
Apply control measures as soon as the first spider mite colonies appear, usually when 2–3 mites per leaf are detected, and repeat applications before fruit sets. Conduct scouting every 5–7 days during warm, dry periods to ensure timely intervention.
When should cucumbers be treated for spider mites in the greenhouse? - in detail
Spider mite infestations develop rapidly under warm, dry greenhouse conditions. Monitoring should begin as soon as seedlings are transplanted and continue throughout the production cycle. Inspect the undersides of leaves at least twice weekly; look for stippling, webbing, and moving mites.
Treatments are warranted when the population exceeds an economic threshold. A commonly used benchmark is five mites per leaf plus any visible webbing. If scouting reveals this level, immediate action prevents exponential growth that can damage fruit and foliage.
Timing of applications depends on the cucumber growth stage. Young vines are more vulnerable because leaf area is limited; therefore, intervene earlier in the vegetative phase. In the flowering and fruiting stages, maintain lower mite numbers to avoid yield loss, but avoid excessive pesticide residues on developing fruit.
Effective control integrates several tactics:
- Cultural measures: keep relative humidity above 60 % when possible; misting reduces mite reproduction. Remove plant debris and weeds that harbor pests.
- Biological agents: release predatory mites (e.g., Phytoseiulus persimilis or Neoseiulus californicus) when populations approach the threshold. Apply at a rate of 1 – 2 million predators per hectare and monitor their establishment.
- Chemical options: use miticides with short residual activity, such as abamectin or spirotetramat, rotating modes of action to delay resistance. Apply according to label rates, ensuring thorough coverage of leaf undersides.
- Resistance management: alternate between at least two different chemical classes and incorporate biological releases to reduce selection pressure.
After any treatment, re‑inspect the crop within 3–5 days to verify efficacy. If mite numbers remain above the threshold, repeat the measure with a different mode of action or increase predator releases. Maintaining a regular scouting schedule and adjusting humidity and ventilation are the most reliable ways to determine the optimal moments for intervention.