Q I know that vandas are susceptible to fusarium wilt, but are cattleyas susceptible as well? I was dividing some cattleyas recently and noted the feared violet ring along the outer edge of the cut surface. I am worried because many of the leaves on my cattleyas have a tough woody texture to them.

A  I am afraid that your cattleyas have fusarium wilt. Cattleyas are just as susceptible as vandas. You can try cutting to see if you can get ahead of it — i.e., get part of the rhizome that is not purple and be careful to sterilize your shears after each cut. However, if you are unable to find clean tissue, you may have to face the inevitable. I am not aware of any fungicide registered for orchids that is effective on fusarium wilt. Authors of the section on fungal diseases in the 2002 edition of Orchid Pests and Diseases Handbook mention an unregistered product called Chipco 26019, a 50-percent wettable powder that shows some activity as a drench to control Fusarium oxysporum. If you wish to try it, be cautious and you may have to make a number of applications before getting any results. If the infected plants are special for you it may be worth the effort.  —Andy Easton.