Summer is when the Palo Verde Borer is most active, especially in the early evening. This large insect is easy to identify. At 3 to 6 inches long, there’s no mistaking it when you see one. They resemble a roach, with long antenna and a spiny collar on their thorax.
Although the name implies they affect only Palo Verdes, this is not the case. Plus, they don’t usually bother our native Palo Verde species, such as the Blue Palo Verde and Foothills Palo Verde. Their favorite target is the Mexican Palo Verde, which long needle-like leaves and messy growth habit. This weedy tree is not a good choice, and is quite invasive.
The grubs of the borer feed on the roots of the Mexican Palo Verde and other non-native trees. They live underground for up to three years. Once the tree shows decline in the form of branch dieback, it is too late to save the tree. A telltale sign that the borer has visited your tree are the quarter size exit holes in the root zone, indicating the borers have done their job and left. Therefore, placing poison in the holes does not help, because the insect long gone and the damage is done.
So what’s a person to do? Planting native species certainly helps, and keeping your trees stress free does too. Insects like stressed plants best. Stress factors include the wrong species for the desert, insufficient (or too much) irrigation, planting too deep, construction damage of roots, and incorrect pruning. As for fertilizing native trees, the answer is don’t. If you are planting desert natives, they do just fine without fertilizer. In fact, most desert trees are in the legume family, and have the ability to fix nitrogen from the air, providing their own source of fertilizer. Don’t waste your money. In addition, fertilizing nitrogen fixing plants only leads to them “forgetting” how to do what nature gave them the ability to do. Overall, keeping your trees healthy is the best way to avoid insect pests and diseases.