Borer

Question:   What is this? I found it on my grapevine.

Answer:  You have a “borer” working in the grape stem. The frass is the borer’s excrement mixed with the sap rising in the canes as the borer is tunneling inside and eating the soft tissues.

Usually, you do not see this in grapes. I have only seen it a few times myself. Just always work back into the mature grapevine – pruning out 2 or 3 feet and you should be able to remove the borer. You cannot use any borer treating insecticides, as the chemical will be in your grapes to eat.

These borer adults will be a hard-shelled insects, not miller moth or butterfly. There are several species some with color and others brown or black, but they will have long antennae. They will become more active as our weather warms up.