I would like to know if the attached picture is wasp damage to my deck? It is not a hole borrowed into the wood. It looks like something was almost scratching at the surface of all the spindles (which are cedar). Please let me know. Thanks.
No doubt this is some kind of insect damage and most likely due to a “girdling” wasp. Common wasps that girdle include EUROPEAN HORNETS, YELLOW JACKETS and BALD FACED HORNETS but there are others. Regardless of the species that’s causing the damage, if you wish to stop it from happening you’ve got a couple of treatment options.
The first would be to leave the wood as it is and spray it down with some CYPERMETHRIN. Wasps hate this stuff and will avoid treated surfaces. Treat as needed; usually 1-2 sprayings per month will keep them away. Mix at the rate of 1 oz per gallon of water.
A more permanent solution would be to sand the wood down and then finish it with some paint or stain. But before you apply the finish, be sure and add some NBS PAINT/STAIN ADDITIVE. The NBS will act as a long lasting residual repellent and need only be applied every year or so. Now if it wears out and the finish is still good, spray with the Cypermethrin should the damaging pests come back.
European Hornets: http://www.bugspray.com/article/eurohornet.html
Yellow Jackets: http://www.bugspray.com/article/yellowjackets.html
Wasp Control: http://www.wasps.net/wasp-and-hornet-control