Michigan State University Extension
Ornamental Plants plus Version 2.0 - 00000308
01/01/98
American anthracnose starts at the tips of the leaves and spreads towards the bases. The diseased areas are dark colored and decayed. Many spore pustules develop in the decaying leaves and stems.
Black rot causes infected leaves to turn purplish brown or black. If the pseudobulb is infected before the leaf, the part above the infection dies.
Leaf blight symptoms are purplish brown or black leaves.
A number of leaf spots attack this species of orchid. Basal rot invades the root collar then extends into the leaves. Infected leaves wilt, discolor, and break off, usually at the base. The base of the stem may be covered with a thick fungal growth.
Petal blight causes spots on the petals. The spots may be bordered by pink rings. If the spots enlarge, the petal may fall off.
Abnormal flower colors may be due to a virus disease called cattleya flower break. The virus is carried by the green peach aphid.