Q There are tiny black spots all over the canes and under the leaves of my dendrobiums. I have looked through six orchid books and cannot find a description that fits my problem. I do not know whether it is fungal or viral. I have used malathion, but see no change. It is beginning to look like every dendrobium I have has this disease (about 50 pots). The new growth does not yet appear to be affected. Shall I chop everything else off and discard, discard all the plants or can this problem be treated?

A  It is unlikely you have a sudden viral problem on all of your plants, especially as the young leaves would appear to be unaffected. I would be much better able to help if I could see some close-up photographs of affected leaves; sending me digital images would allow me to do that. Your problem would appear on first reading to be either fungal or bacterial, except that I would expect the young leaves to be possibly even more heavily damaged than the mature ones. It is useless to apply malathion in your situation as it has to my knowledge only insecticidal properties and would be ineffective for fungal or bacterial problems. Until the problem can be determined, try to make sure your dendrobiums are watered early in the day and that they stay as dry as possible at night.  To learn more about basic dendrobium culture, you can request a care sheet from the Society's Membership Services Department (telephone 561-404-2000; fax 561-404-2100; e-mailTheAOS@aos.org) or download a .pdf file from our Web site, orchidweb.org.—Andy Easton.