Yucca plants with yellow, droopy leaves may be infested with pests. Look for signs of pests by inspecting the undersides of the leaves and stalk of the plant. Small red dots, for instance, indicate the presence of spider mites. Wash the plant thoroughly using a garden hose, and then spray the plant with a mixture of 2 tablespoons of dish detergent and 1 gallon of water to eliminate pests.
Overwatering a yucca plant can also cause discoloration of leaves. Other signs of overwatering include a spongy trunk, dark brown roots and the eventual death of the plant. To prevent overwatering, allow the soil to dry out for several days, and use a container that drains well. Replant the yucca in a container in a clay pot, if necessary, and then place the container in a sunny location to prevent root rot and other diseases from affecting indoor yucca plants.
Poor lighting may cause yucca plants to die. The leaves of the plant may initially turn dark green, then fade to yellow if inadequate sunlight is causing the problem. Yucca plants need several hours of full sunlight each day. Place the yucca in a sunny window indoors, or move it outdoors for several weeks to revive the plant.Learn more about Outdoor Plants & Flowers