Bamboo plants are giant grasses with large, woody stems (culms). The culms have sections called internodes that have clearly discernible joints (nodes) all along their length. Bamboo spreads by sending out rhizomes, underground stems that come up and grow into more bamboo culms. Bamboo plants are generally pretty tough, but they occasionally experience a few problems.
Fungal spots are mainly cosmetic, but they are unsightly. They generally appear in a circular pattern on older bamboo culms. You can treat fungal spots with an antifungal product containing copper, or just cut the affected culms out and discard them.
Bamboo Mosaic Potex Virus (BaMV)
A virus that causes a mosaic pattern on the leaves of bamboo, BaMV generally spreads when gardeners use cutting tools that have been infected with the virus on uninfected plants. In its most extreme form, the disease can kill bamboo, and there is no known cure. Fortunately, most reputable bamboo nurseries carefully test their plants to make sure they don't have the virus and will not sell infected plants.
One species of bamboo in particular, Dendrocalamus latiflorius Mei, carries and spreads the virus without being affected by it. Consequently, bamboo dealers advise that you not grow this variety, but if you do, you must disinfect any tools you use on the plants before using them elsewhere.
Black Sooty Mold
This mold affects bamboo species that have dense branches growing out from their nodes. Aphids feeding on bamboo secrete a substance that attracts the mold. Treat by washing the mold off with jets of water, or by taking measures to control aphids on your bamboo plants.
Scale are tiny insects that feed on the bamboo's juices. The plants seem mostly unaffected by the insects, but they can multiple to the point where they completely cover the culms. Treat scale by spraying them with water or with systemic insecticides that the pests will ingest. You can also try treating the bamboo with insecticidal soaps or oils.
Bamboo Mealybug (Palmicultor lumpurensis)
Mealybugs only infest bamboo plants. You can identify the mealybugs by looking for white webbing attached to the new shoots of the plants. If you find such a substance, look beneath the leaves for tiny pink bugs. Usually mealybug infestations don't bother bamboo plants very much, but in cases of severe infections, the culms and shoots can abort.
You can treat mealybugs by introducing natural predators like the mealybug destroyer (Cryptolaemus), but such efforts usually aren't effective in the long run because the predators leave once the food supply is exhausted.
You can also treat mealybug infestations by spraying the bamboos thoroughly from all sides with a systemic or contact insecticide designed for the insects, combined with some mild dish soap to help penetrate the bugs' webs. Reapply the insecticide every 10 to 14 days, at least three times, even if you don't see any mealybugs after the first or second application.