Cooperative Extension Fresno County
University of California
Cooperative Extension Fresno County



Q. Small branches and twigs have completely died back on my deciduous fruit or nut trees. There are small round holes in the bark and what looks like sawdust (it's called frass-bug excrement and wood particles) coming out of the holes. Or, there may be sap oozing through cracks in the bark, but no frass. What causes this?

Flat head borer
 A. The holes and sawdust (frass of peachtree borer) or oozing sap (Pacific flathead borer) are signs of borer infestation in the trees. Shothole borers make very tiny holes. Borers tend to attack newly planted, stressed, sunburned or unhealthy trees so the first thing to do is to correct any cultural problems. Make sure that the tree is properly fertilized and well-watered through the year and is properly pruned, leaving enough branches to provide shade that will help prevent sunburn. The trunk and exposed branches can also be painted with a half and half mixture of white latex paint and water as extra protection against sunburn. Cut out any infested wood and dispose of it or burn it-do not put it in the compost pile or leave in the yard.  Spraying is not recommended for shothole or Pacific flathead borers. Several control methods are possible for eliminating peachtree borer. The larvae of clear-wing moths can be skewered and killed with a sharp wire poked into their holes. Refer to pest notes for more information on controlling and preventing borers.

Pest Notes:  Pacific Flathead Borer  Clearwing Moths  Roundheaded Longhorned Borers   Shothole Borer on Plum    Peach Twig Borer on Nectarine


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