Dieback of small oak branches caused by scale insects

During August in central Minnesota, leaves on some oak twigs and small branches turned brown. Inspection revealed scale insects (Parthenolecanium quercifex or P. corni). When these insects insert their piercing-sucking mouth parts through the bark or leaf veins and feed on sap they cause gradual leaf and twig death. Feeding by scales is seldom noticed until large numbers are present, and many groups of green leaves turn brown.

Where high populations of scale occur natural control organisms, especially lady beetles, fungi, and chalcidoid wasps attack and will often reduce scale numbers before much damage is done. When chemical control is necessary a dormant oil applied before leafing out occurs, or the application of a systemic or contact insecticide against the nymphs are effective.