Brown leaf spot
on Yucca
Coniothyrium concentricum
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Identification
Coniothyrium leaf spot first appears as tiny clear zones in older leaves of Yucca. Spots turn yellowish and finally brown as they mature. They are generally elliptical and are scattered across the entire upper surface of older leaves. After about 4 months, black fruiting bodies form in sunken centers and are easily seen with the naked eye. Sometimes a yellow border forms around the spots. This disease has been reported on many species of Yucca including Y. aloifolia, Y. filamentosa (Adam's needle), and Y. smallianaPrevention
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.