Issue 7, June 6, 2011
Emerald Ash Borer Detection
Emerald ash borer adults are likely to emerge within the next week or two in Illinois. In previous years, adults have started emerging in Chenoa, IL around June 8. Adults would be likely to start emerging in Illinois north of I-80 around mid-June. Although it takes some diligence to find adult beetles in low level infestations, the emerging beetles leave behind new emergence holes on trunks and branches and marginal feeding damage on ash leaflets. These increase the likelihood of discovering infested trees. A photo of their leaf feeding damage was in last week's issue of this newsletter.
I find it easiest to detect emerald ash borer emergence holes on branches up to three inches in diameter. The bark on these smaller branches is still smooth enough that the holes are easier to spot. Unfortunately, branches this small are unlikely to be present any closer than eight to ten feet above the ground on pruned landscape trees. Binoculars are useful in spotting these holes. On the trunk and larger branches, where the bark is rough, shaving down the outer layers of bark with a pocket knife helps reveal the true shape and size of suspicious holes.
Many other borers commonly attack ash trees under stress, and some of them leave emergence holes that can be confused with the one-eighth inch diameter D-shaped holes made by emerald ash borer. Redheaded ashborer adults leave one-eighth inch diameter round holes when they emerge. Emerging ash and privet borer adults leave three-sixteenth inch diameter oval holes. Flatheaded appletree borers also attach ash, with the beetles leaving three-sixteenth inch diameter D-shaped holes when they emerge. An overview of these and other borers common in ash, including photos, was published in this newsletter in 2007. (Phil Nixon)