Anthracnose
(fungus - Colletotrichum (Gleosporium) spp.)
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Identification
This disease affects several kinds of cacti, Cereus, Echinocactus, Mammillaria, and particularly Opuntia (prickly pear). Infection results in a rather moist light brown rot which shows many light pink pustules on the surface. Spots are small at first, later enlarge and become covered by the small spore-producing pustules. Eventually, the plant tissue dries up and becomes hard and bark-like. Large areas may be affected, sometimes destroying entire plants.This disease also appears frequently in autumn in agaves grown in the open air when the weather gets very wet, from the lowest leaves. During the winter the disease goes to the heart of the plant. The leaves most affected should be cut in spring.
Prevention
As always, good greenhouse hygeine and making sure only healthy plants are introduced to the collection
Disease is spread by splashed water. Take special care of rooting cuttings.
Cure
No really satisfactory control is available, other than removing and destroying diseased parts in the initial stage, they can be cut back to healthy tissue using a knife that is repeatedly disinfected by passing it through a flame or dipping it in medicinal alcohol.In the greenhouse, soil from infected plants should be removed and benches disinfected. Spraying with a copper fungicide, Maneb, Benomyl or Dithane may help in checking the disease.