Brown Leaf Tips on a Yucca Tree

Diseases

• Yuccas are vulnerable to several fungal diseases that can discolor leaves and stems. One of them, gray leaf spot disease, causes the tips and edges of yucca leaves to turn gray or brown. Other diseases, like Fusarium stem rot, can damage and discolor yucca leaves by infiltrating the stems or roots of the plant.

Pests

• Feeding by insect pests may cause the leaves of yucca trees to be discolored, to wilt or to curl. Mealybugs, scales and weevils are among the most common pests of yucca in the United States. Mealybugs can attack both the roots and leaves of their host. Initial symptoms of root damage include the discoloration and wilting of foliage, followed by failing stems and possibly the death of the entire plant. Scales and other sap-sucking insects, like aphids, thrips and mites, drain vital fluids from yucca leaves.

Environmental Stress

• Environmental factors can affect the condition of yucca foliage. Freezing temperatures can harm unprotected yucca plants outside of their warm, natural range. According to the University of Arizona, symptoms of freeze damage include dark discoloration of affected parts of the plant, including leaves. Superficial frost damage will fade over time, but severe damage from a lengthy period of freezing temperatures can be lethal, even to established plants. The presence of fluoride or excess salt in the yucca's soil also can cause tissue along the edges of yucca leaves to turn brown.

Management

• Leaves with fungal growth should be removed promptly and discarded to prevent the pathogen from spreading to healthy tissue or surrounding plants. Some fungicides are suitable for controlling fungi on yucca. Water yucca at its base, rather than saturating the plant's foliage, to help prevent fungi from growing. According to the University of Florida, raising the pH levels of the soil by adding lime reduces damage done by fluoride. Most of the common insect pests of yucca can be controlled by applying insecticide to the soil.