Palo Verde Tree scale

Asked September 16, 2016, 7:39 PM EDT

I have a mature Palo Verde Tree in my back yard that has what appears to be some kind of white scale on the trunk and several main branches. Almost looks like cement or mortar. On some of the smaller limbs there are some blemishes that look like they might be eruptions in the bark. Happened to see a woodpecker working very hard on one of these areas yesterday. Tree seems to be losing some leaves. How do I save this tree?

Maricopa County Arizona

1 Response


I can't see the insects in your photos so it would be good to see it closer up or in person. The tree does have the look of a scale insect infestation but it's hard to be sure without a closer inspection. There is a species of scale insect that infests palo verde trees, especially those in urban environments. In some cases, the scale population is so high that they completely cover the bark on parts of the tree. The appearance you described begins with small eruptions in the bark. I’ve seen many like this in downtown Tucson and on the University of Arizona campus. While these insects will feed on sap and reduce the vigor of the trees, they aren’t likely the primary problem. Trees in urban areas surrounded by buildings and other hard surfaces are subject to more stress than the trees out in the open desert. Scale insects, like many other insects, seem to be attracted to stressed trees. So there are a couple things you can do. One is to take good care of your tree if you aren’t already properly irrigating and pruning. The second is you can treat the trunk where the scale insects reside. Typically, the recommendation for scale management is a horticultural oil spray when the immature scale insects, called crawlers, are moving about the tree. This usually happens in late winter once the weather warms sufficiently for them to reproduce. The exact timing depends on local microclimates but usually there is at least a two-week window. Keeping an eye on the situation with a magnifier should allow you to see when the immature scale insects are active.