How to treat a polycarbonate greenhouse in autumn for spider mite control? - briefly
Apply horticultural oil early in the fall, thoroughly coating foliage and repeating every 7‑10 days until temperatures fall below 10 °C; this suffocates spider mites and disrupts their life cycle. If populations remain, follow with a low‑toxicity miticide such as abamectin, maintaining adequate ventilation to avoid excess humidity.
How to treat a polycarbonate greenhouse in autumn for spider mite control? - in detail
Treating a polycarbonate greenhouse in the fall to suppress spider mites requires a systematic approach that combines cultural, physical, and chemical tactics.
First, reduce the environment that favors mite development. Lower the night temperature gradually to 10‑12 °C, but avoid rapid cooling that could stress plants. Increase ventilation to maintain relative humidity above 60 % whenever weather permits; higher humidity interferes with mite reproduction. Remove fallen leaves, dead plant material, and any debris that can harbor eggs.
Second, implement physical barriers. Install fine mesh screens on vents and doors to prevent ingress of adult mites and their wind‑dispersed stages. Apply a thin coat of horticultural oil on leaf surfaces early in the season; the oil smothers mobile stages and also acts as a repellent.
Third, introduce biological agents. Release predatory phytoseiid mites (e.g., Phytoseiulus persimilis or Neoseiulus californicus) at a rate of 10–15 predators per square meter. Ensure the greenhouse remains free of broad‑spectrum insecticides that could harm these allies.
Fourth, schedule targeted chemical treatments only if monitoring indicates population thresholds have been exceeded. Use acaricides approved for polycarbonate structures, such as sulfur‑based products or spinosad, applying them at the recommended concentration (typically 0.5–1 ml L⁻¹) and rotating modes of action to delay resistance. Apply sprays in the early morning or late afternoon to minimize photodegradation and leaf burn.
Fifth, monitor continuously. Place sticky traps on the lower third of the greenhouse frame and inspect them weekly. Count mites on randomly selected leaves (30 cm² each) and compare numbers to established action thresholds (e.g., 5 mites per leaf). Record temperature, humidity, and ventilation settings to correlate environmental changes with population dynamics.
Finally, prepare for post‑harvest sanitation. After the growing season ends, thoroughly clean the greenhouse interior with a mild detergent solution, rinse, and allow the structure to dry completely before sealing it for winter. This eliminates overwintering sites and reduces the initial mite load for the following season.
By integrating environmental management, barrier methods, biological control, judicious pesticide use, and rigorous monitoring, growers can effectively limit spider mite infestations in polycarbonate greenhouses during the autumn period.