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Missouri Department of Conservation Forest Entomologist Robbie Doerhoff urged Missourians who own ash trees in areas where EAB has been found to make a plan now to either treat or remove those trees.

Foresters with the Missouri Department of Conservation, working with the Missouri and U.S. departments of agriculture, recently confirmed the presence of Emerald Ash Borer in 11 new counties across Missouri. New detections have been confirmed in Adair, Callaway, Cape Girardeau, Cole, Greene, Jefferson, Lewis, Lincoln, Pike, Polk, and Warren counties. Since EAB was first detected in Missouri in July 2008, the tree-killing pest has spread to a total of 53 Missouri counties and the city of St. Louis.

EAB is a small, metallic green beetle native to Asia that attacks only ash trees. The adult beetle does very little damage, but in its larval stage, EAB bores into the vascular layer of ash trees, creating distinct S-shaped galleries that slowly cut off the trees' flow of water and nutrients and eventually cause the trees to die. EAB kills more than 99 percent of the ash trees it attacks within three to four years of infestation.

MDC Forest Entomologist Robbie Doerhoff urged Missourians who own ash trees in areas where EAB has been found to make a plan now to either treat or remove those trees. "If you have a healthy, high-value ash tree in your yard, it can be treated with insecticides that will protect it from EAB. However, these treatments must be applied every year or two to guarantee protection," Doerhoff said. "For some ash trees, especially those that have already lost more than 50 percent of their leaves and branches, the best option is removal, followed by replanting with a different species, such as an oak native to Missouri."

Insecticide treatment options are available, including some do-it-yourself methods, but the department said it's important to note that insecticides available at home improvement stores work best on trees smaller than 20 inches in trunk diameter, when measured 4.5 feet from the ground. For larger trees, insecticides available only to licensed applicators are needed.

"If you decide to treat your ash tree, make sure you use a pesticide labeled to kill EAB and that you apply it at the right time of year," said Doerhoff. "Chemical treatments are most effective in early spring when a tree's vascular system is better able to take up the insecticide. In late summer, and especially during drought conditions like we're currently experiencing across most of Missouri, treatments may not work properly."