Last summer, I was checking out one of my favorite trees - a Mexican Sycamore next to the creek in my neighborhood. While I was standing under it getting the bark picture (above), I noticed that some of the leaves had holes in them and some were showing signs of "stippling" (light yellow spots) on the upper sides of the leaves. I picked a leaf with the most damage showing:
That leaf looks pretty bad, and if every leaf on the tree looked that, I'd be pretty concerned. But most of the leaves looked undamaged and fine. I turned the leaf over to see if I could see what was causing the stippling:
Hmmm, lots of little black dots and are those insects? Let's get a closer look:
Oh wow, those are pretty small and they look somewhat familiar. Could they be lace bug larvae? A quick google image search informs me that I'd remembered correctly and they are the larva of a lace bug. All those little black dots? Are their excrement. Yuck!
Lace bugs are "true bugs", in the Hemiptera order (hemi meaning half and ptera meaning wing). They have piercing/sucking mouthparts and feed by piercing the underside of the leaf and sucking the sap - much like aphids.
In general, the damage caused by lace bugs is mostly aesthetic. A healthy, unstressed tree will overcome the damage easily and barely even pause as it continues growing. If the infestation is really heavy, it could cause the tree to lose vigor and stress it to the point of being vulnerable to other insects and diseases, but this is generally pretty rare. For the most part, the damage caused by lace bugs is more offensive to humans than to the tree.
We humans want everything to look "perfect" and see the stippling as a sign of imperfection and a problem to be corrected. But be careful in your correction. Lace bugs are controlled by beneficial bugs - lacewings (similar name, but not at all like a lace bug), ladybugs, assassin bugs, and wasps will all prey on them. If you spray a contact insecticide, you run the risk of killing off your allies right as they're really ramping up reproduction to step in to provide control.
So what can you do if your tree has lace bugs that won't harm your natural allies? First make sure you've got a nice mulch ring around it; this will reduce competition from grass, hold moisture, and keep the ground cooler. Then, make sure it is watered regularly, either by nature or by you. An inch of water each week is generally sufficient. Do not fertilize the tree unless a soil test shows that it is deficient in nutrients, then only provide the nutrients that are deficient; too much is as bad as too little and can sometimes make the problem worse - for example excess nitrogen can actually attract aphids.
If the tree starts showing signs of distress and the infestation moves to covering half or more of the leaves on the tree, call an ISA Certified Arborist, like me. You can also find one at http://www.isa-arbor.com/findanarborist/findanarborist.aspx and in Texas you can use ISA Texas' "Find an Arborist" app at http://isatexas.com/for-the-public/find-an-arborist/. A Certified Arborist can advise you on methods of control, if needed, and help you prepare a plan of action. Before long, your tree will be back to its normal, healthy, beautiful self.
