By Paul Cigan, DNR Forest Health Specialist, Hayward, Paul.Cigan@wisconsin.gov or 715-416-4920
Twolined chestnut borer (TLCB) attacks on oak trees have increased in numerous Wisconsin counties, with decline and associated mortality in the last two growing seasons, most noticeably since August.
Symptoms of infestation by this native beetle are initially seen in mid-July on the outer portions of branches in the upper crown. Leaves begin to fade from green to yellow to red. Within a matter of weeks, they turn brown and remain on the branches for weeks to months. Their foliage may also appear sparse or completely bare (Fig. 1).

Figure 1. Northern red oaks with symptoms of twolined chestnut borer, ranging from crown thinning and leaf chlorosis like the tree on the left (early stage) to dead top branches like the tree on the right (intermediate stage). Photo: Wisconsin DNR
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