Q. I have a five-foot yucca tree that I cannot get to be disease free after two years of trying.  I have tried the following chemicals; Bayer Advanced complete Insect Killer, Bonide Thuricide and Bonide Tree and Shrub Insect Control Systemic. Any suggestions on how to save it. Judging from the picture and your problems it might be Spanish Dagger, a native of the SE part of the US. Spanish Dagger, Yucca gloriosa, does not handle the heat and should not be planted in south or westerly landscapes. Not sent to me by the author. A. Judging from the picture you sent to me your yucca tree is Yucca gloriosa, a.k.a. Spanish dagger. Spanish dagger is a yucca native to the SE that gets brown spots on its leaves that resemble disease but it is either planted in the wrong location or planted incorrectly or both. This plant is both mesic (high in its water use) and not a desert yucca native. Looks like Yucca recurvifolia (aka Y. pendula) another yucca native to the southeastern and southern US that may scorch if planted in a hot location. Readers picture. Spanish dagger is an Eastern coastal native from South Carolina to Florida. If planted in our desert Southwest, this yucca will look diseased if it’s planted on the West or South sides of a home, surrounded by rock, or watered like a cactus. Because it’s a native of the southeastern United States, Spanish dagger should be planted so that it gets shade in the afternoon; on the East or north side of a home landscape in afternoon shade. Also, plant it with compost amending the soil and surrounded by other mesic plants to help moisten the soil.