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Anthracnose Infection of Mirliton Leaves (chayote, “Sechium edule”)

Anthracnose plant disease affects almost all mirlitons at some point. If you are fortunate, it will follow and kill only one stem which will be replaced by a new shoot. There is no effective organic fungicide but a plant will increase resistance to the disease every year of its life. Note the brown necrotic tissue and typical splash-up of soil-borne spores, migration of the fungus in a linear fashion up the plant. Disease starts as yellow patches on leaf or leaf margins (edges). Then interior turns paper-brittle brown and "shot holes" can appear in middle.
Typical "margin wedge" pattern from the leaf edge – fungus is drawing nutrients from dying tissue. Leaf nearly all dead (necrotic). Some "square" patching of green in yellow area, another sign of anthracnose. These leaves contain spore-bearing structures that can survive for more than a year, so dead leaves should be picked off and disposed off-site (never composted).
Perfect example of anthracnose. Starts on living tissue then lives on dead tissue. Note distinctive anthracnose "shot hole" in middle of now dead tissue where fungus has fed on dead tissue--unlike powdery mildew. Wedge-shaped yellowing or brown (dead) patterns starting at the leaf edges distinguish anthracnose from powdery mildew. Anthracnose travels through plant cells so tends to follow leaf vein design. Powdery mildew spreads on surface of leaf so less conformity to leaf vein structure (initial yellow splotches overlap veins) and more generalized yellowing of entire leaf and browning/wiling of entire leaf simultaneously.
Note on edge where yellow tissue meets green that the yellowing tissue tend to follow square leaf vein structure. Anthracnose also tends to move more quickly through the leaf since it extracts nutrients from both living and dead tissue. Dead tissue starting on leaf edges (margins). In the early morning, root pressure in plants with excess water will emit water drops at the leaf edges (guttation) through glands called hydathodes. This fluid can provide the additional water that anthracnose needs to germinate, so infection often proceeds from leaf edges.
Perfect example of anthracnose. Starts on living tissue then lives on dead tissue. Note distinctive anthracnose "shot hole" in middle of now dead tissue where fungus has fed on dead tissue--unlike powdery mildew. Wedge-shaped yellowing or brown (dead) patterns starting at the leaf edges distinguish anthracnose from powdery mildew. Anthracnose travels through plant cells so tends to follow leaf vein design. Powdery mildew spreads on surface of leaf so less conformity to leaf vein structure (initial yellow splotches overlap veins) and more generalized yellowing of entire leaf and browning/wiling of entire leaf simultaneously.