Brown Spots on the Spineless Yucca

Recognizing Brown Leaf Spot

• A few different fungal leaf spots may affect yucca, but Coniothyrium, or brown leaf spot, caused by the pathogen Coniothyrium concentricum, is the most prevalent; all are prevented or addressed similarly. Brown leaf spot first appears on older yucca leaves as tiny clear areas that eventually turn yellow, then brown. These lesions appear on upper leaf surfaces and are usually elliptical. A chlorotic halo or dark margin may form around older lesions, and after about four months dark fruiting bodies become visible in the lesion centers.

Leaf Spot Prevention and Treatment

• To prevent or address problems with fungal leaf spots on the spineless yucca, remove older leaves and any leaves that have spots or are shriveled, as well as any fallen leaves and other debris around the yucca plant. Avoid overhead or sprinkler irrigation around the spineless yucca, and protect the plant from rainfall, if possible. Leaf spots on a yucca are rarely serious and do not impact the plant's overall health.

Scales

• Scales usually appear as small, immobile tan or brown bumps where they feed on spineless yucca stems and foliage. They often have no recognizable body parts. Heavy scale feeding can cause leaf wilting and yellowing, and premature drop. Scales have many natural enemies that usually control them on outdoor yuccas unless these beneficial predators are interrupted by dust, ants or broad-spectrum, persistent pesticides. Prune off heavily infested portions of the spineless yucca and provide the plant with good cultural care to curb scale activity.

Mites

• Spider mites -- eight-legged pests that look like tiny, moving dots to the naked eye -- are occasional yucca pests. Their feeding damage appears as a tan or gray stippling on foliage and is often accompanied by indicative webbing. Leaves may develop a broader yellow or bronze discoloration, and the plant may decline. Mites prefer dry, dusty conditions. Occasionally spray the spineless yucca with a forceful stream of water to knock these pests off and alleviate the dusty conditions they prefer. Make sure you time any water sprays for early morning so water will evaporate quickly and not lead to problems with fungal disease.