Pest and Life Cycle – (Stigmaeopsis celarius & S. longus) – Both these bamboo mite species (formerly Schizotetranychus) are found in the Pacific Northwest. They are most active during warm weather (starting in spring) and go through 5 distinct life stages, eventually forming large colonies on the reverse of the leaves that are protected by dense webbing (which makes them difficult to control). As they feed on the foliage, tissue is damaged and the plant loses some of its ability to photosynthesize, reducing vigor.
Symptoms – Patterns of cream-coloured bars or elongated blotches appear on the upper surface of the leaf which are a result of the mites feeding on the underside – starting at the base of the leaves. This mottling is often mistaken for a nutrient deficiency or variegation.
Management – Bamboo Mites are difficult to control with sprays, as they are located on the leaf reverse and are also protected by dense webbing. That said, you can try controlling small outbreaks by bending the canes and spraying the undersides with either horticultural oil or insecticidal soap. This method is not usually effective in large stands with serious infestations, so some gardeners achieve control by cutting down all the stems in early spring before the new culms or shoots emerge. It is important to remove or destroy all the cut canes and leaf litter on the ground, but if done properly the new shoots should emerge mite free. Your final option is biological control or predator mites, which may only be effective in contained areas – inquire at your local garden centre for the availability.
Prevention – 1. Inspect newly acquired bamboo plants carefully for infestation and consider quarantining them for a period of time before planting in the ground. 2. Thin out dense bamboo groves by 50% (removing older or weak culms first) to improve air circulation and make it harder for mites to establish dense colonies. 3. Some bamboo growers hard spray their plants with a pressure washer from time to time in order to dislodge existing bamboo mites and keep the population threshold (and symptoms) down.
Mike's Garden Guide 