What immediate actions save plants with severe spider mite damage?
Written by
Liu Xiaohui
Reviewed by
Prof. Martin Thorne, Ph.D.Severe spider-mite infestations require immediate emergency measures. Immediately isolate the infested plant at least 10 feet away from any other plants to control the dissemination. Prune the plant by removing all leaves with over 50% damage, using sterilized shears. Last summer, this method saved my dying hibiscus, after the stems were covered with webbing.
Isolation and Pruning
- Move plant immediately to separate area minimum 10 ft (3m) away
- Prune all leaves showing >50% damage or dense webbing
- Sterilize tools with 70% alcohol between each cut
- Dispose infected material in sealed bags never compost
Intensive Treatment
- Apply high-pressure water blasts at 40 PSI daily for 7 days
- Introduce Phytoseiulus persimilis predators at 1:5 ratio
- Combine with neem oil applications every 72 hours
- Maintain quarantine for 21 days post-treatment
Administer high-pressure water treatments correctly. Use hose nozzles adjusted to 40 PSI (2.8 bar) and direct them onto the undersides of the leaves. Spray early in the morning so that the plants dry before dusk. I angle my nozzle up so that I can blast the mites out of the joints of the stem. Continue to spray daily, even after the mites appear to be gone, to eliminate the hidden eggs.
Place predatory mites tactically. Disperse Phytoseiulus persimilis directly on infested web areas at 1:5 ratio predator-prey. It is necessary to keep humidity over 60% for their continued existence. I plan sachets in heavily infested boughs of my greenhouses. They begin feeding within hours while sprays take longer.
Combine neem oil and biological controls with care. Use a solution of 2 tablespoons per gallon at dusk, three days after predators have been released. Care should be taken to avoid spraying predators directly. I use a paintbrush to apply the neem oil to stubborn colonies. This two-pronged approach saved my citrus trees during times when either method alone could not accomplish the task.
Monitor recovery closely. Check for new stippling daily with 10x magnification. Isolate for 21 days after the last scab sighting. I log my calendar to check root health once a week. Severely damaged plants often need extra nutrients to revitalize, so fertilize conservatively.
Read the full article: Ultimate Spider Mite Control Guide
