We tend to see fungal leaf spots and blights in spring and early summer. For many diseases, this is because weather conditions are conducive to infection and the new foliage is most susceptible. Once leaves develop a thickened cuticle, they are more resistant.
Yuccas are occasionally bothered by fungal leaf spots, and this year’s weather encouraged infection. Several fungi, including Cercospora, Cylindrosporium, and Coniothyrium may cause leaf spoting but do not cause widespread death of leaves. Coniothyrium leaf spot seems to be the most common of these. It is also known as brown leaf spot because the lesions turn brown. Often a yellow halo is present. Remove leaves that are spotted or shriveled because the fungus continues to sporulate on those leaves. Avoid overhead irrigation and consider the use of a fungicide to get the disease under control if overhead irrigation cannot be avoided. Weekly applications of copper fungicides or Bordeaux mix help stop disease spread. Be sure to check the label of the chosen product for clearance on yucca, recommended rates, and timing before making any applications.