Q. I have a five-foot Yucca tree that I cannot get to be disease free after two years of trying. I have tried several insecticides and fungicides. I hope you can identify the problem from the picture.
A. The Yucca leaves are scorching or turning brownish white in the middle, at the bend where the leaf is curving down. This is not a problem you can correct by treating with insecticides or fungicides.
This is an ornamental Yucca called Spanish dagger with flat leaves coming from the trunk and curving slightly downward. You would think that yuccas would be a plant not requiring much care in the Mojave Desert. Well, this one does. It is native to coastal Carolinas, Georgia, Florida and Alabama.
This is a cultural management problem. It should be addressed by transplanting it to a new, protected location and adding amendments the soil at the time of planting. Water it more like a palm tree than a cactus.
Although classified as a disease, it is not caused by anything biological so pesticides won’t do any good. This problem is more correctly classified as “leaf scorch”. It is a soil/planting location/water management problem.
Don’t plant this Yucca like you would yuccas that grow easily in desert environments. This particular Yucca prefers protection from the hot, late afternoon sun and grown in richer soils, soils amended with compost at the time of planting, and not surrounded by rock mulch.
What to do now? Move it to a new location which gives it protection from direct, late afternoon sun. If it is surrounded by rock mulch, get rid of it. With a posthole digger or soil auger make several vertical chimneys in the soil about two feet deep and 18 inches from the trunk. Pack these vertical chimneys with compost and then soak them with water.Water this plant like a normal landscape plant with good drainage and make sure it is watered on four different sides with enough water each time to percolate 18 inches deep.