A relatively problem-free plant, bamboo is used in both landscape design and as a houseplant. It is an evergreen perennial that grows quickly and can spread to cover a large area. Bamboo can be infested by scales and spider mites, with both pests causing white spots. Controlling these pests is not difficult, but it is important to the survival of your bamboo.
Scales and spider mites are the most common pests of bamboo, according to the University of Kentucky. Scales are small insects that attach themselves to a plant and feed on the sap in leaves and stems. Soft scales are covered in a protective coating of waxy filaments that look like white cotton. These immobile insects can look like fuzzy white spots on your plant. Hard scales are also immobile but are covered in a hard shell. They can look like scabby white spots on leaves and stems. Spider mites are members of the arachnid family and also feed on sap. They are very small, round-bodied pests that can be difficult to see.
Feeding by scales can cause yellowing and wilting of plants. Plants may look unkempt and their growth may be stunted as well. Extreme infestations can cause the death of all or parts of a bamboo shoot. Plants weakened by scale feeding may also be more susceptible to secondary infections by viruses or fungi. In addition to the damage they do while they feed, scales excrete a sticky substance called honeydew that attracts a black fungus called sooty mould.
Spider mites cause a white stippling on leaves as they feed. As they continue to feed and their feeding spots merge, leaves turn yellow or bronze and drop off the plant. Extensive infestations can cause death. Spider mites can also coat the plant in a fine webbing that attracts dirt and mould. This webbing is more unsightly than it is dangerous.
Knock spider mites off plants with a strong jet of water from a hose for outdoor plants or a spray bottle on the stream setting for houseplants. Scales can be wiped off with a damp rag. Predatory mites are available at some garden centres and can provide chemical-free control for a spider mite infestation. Pruning out heavily infested leaves or shoots can help prevent either pest's infestation from spreading.
Chemical control of scales can be difficult since they are covered in protective coatings. Time applications of insecticides at egg laying or as immature scales are emerging. Immature scales, called crawlers, are not yet protected and are more susceptible to insecticides. Spider mites can usually be controlled with horticultural oils or insecticidal soaps. If severe infestations require harsher chemicals, miticides are available. If you purchased predatory mites, avoid the use of chemicals as they will kill predatory mites too.