Grey leaf spot
on Yucca
Cytosporina sp.
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Identification
Cytosporina or grey leaf spot of Yucca aloifolia (Spanish bayonet) has not been adequately described. Symptoms include tip and marginal necrosis with a predominantly gray colour and brown margin. They often reach 3 inches wide, have concentric rings of light and dark tissues and are most common on older leaves. The black fruiting bodies of Cytosporina sp. can be found in these spots. This disease is not as common today as it was 20 years ago.Prevention
Cure
One of the most important aspects of control is the removal of older infected leaves and elimination of overhead watering or exposure to rainfall.
Since most yuccas are grown exposed to both overhead watering and rainfall, regular applications of fungicides are needed to prevent disease. Weekly applications of chlorothalonil, zineb (Zineb), or mancozeb provided excellent disease control experimentally.