Emerald Ash Borer FAQ

Early infestations of emerald ash borer are nearly impossible to detect as the tree does not immediately show outward symptoms; however, as the infestation grows,the tree will decline and ultimately die. 

An EAB infestation is generally first detected by the yellowing and dropping of leaves in the upper canopy of the tree. And as the infestation progresses, more branches will die and the tree will sprout new shoots from the lower trunk to replace them. 

After the first year of infestation, small D-shaped exit holes (approximately 1/8 inch in diameter) will appear on the trunk as the mature beetles exit the tree to begin the next egg-laying cycle. Splits in the bark may then develop revealing the damaged phloem layer beneath. Woodpecker holes are also common in an infected tree as the birds search for the larvae. 

Arborists and other tree management officials generally use the percentage and location of canopy damage and branch dieback to determine whether an infected ash tree is treatable and worth saving. A homeowner would be wise to assume that if there are diseased ash trees nearby, his or her tree(s) is also probably infested even if it is not yet showing the symptoms.

Once an ash tree loses over 50% of its canopy, it is not treatable, according to scientific consensus.  Once an ash tree dies, it does not maintain its structural integrity compared to other tree species like oaks or the American elms that were killed from Dutch elm disease.  Homeowners should have dead ash trees removed as soon as possible. A dead ash can drop large limbs and may fail in wind or ice storms. Property damage, power outages and human injuries may occur.

The economics of treating ash trees with insecticides for EAB protection are complicated. Factors that can be considered include the cost of the insecticide and expense of application, the size of the trees, the likelihood of success, and potential costs of removing and replacing the trees. Until recently, insecticide products had to be applied every year. A new product Tree Age, that is effective for two years or even longer (emamectin benzoate) has altered the economics of treating ash trees. 

Benefits of treating trees can be more difficult to quantify than costs. Landscape trees typically increase property values, provide shade and cooling, and contribute to the quality of life in a neighborhood.   

It is also worth noting that the size of EAB populations in a specific area will change over time. Populations initially build very slowly, but later increase rapidly as more trees become infested. As EAB populations reach their peak, many trees will decline and die within one or two years. As untreated ash trees in the area succumb, however, the local EAB population will decrease substantially. Scientists do not yet have enough experience with EAB to know what will happen over time to trees that survive the initial wave of EAB. Ash seedlings and saplings are common in forests, woodlots, and right-of-ways, however, and it is unlikely that EAB will ever completely disappear from an area. That means that ash trees may always be at some risk, but it seems reasonable to expect that treatment costs could eventually decrease as pest pressure declines after the EAB wave has passed.

Recent research shows that the beetle can have a one- or two-year life cycle. Adults begin emerging in mid to late May with peak emergence in late June. Females usually begin laying eggs about 2 weeks after emergence. Eggs hatch in 1-2 weeks, and the tiny larvae bore through the bark and into the cambium - the area between the bark and wood where nutrient levels are high. The larvae feed under the bark for several weeks, usually from late July or early August through October. The larvae typically pass through four stages, eventually reaching a size of roughly 1 to 1.25 inches long. Most EAB larvae overwinter in a small chamber in the outer bark or in the outer inch of wood. Pupation occurs in spring and the new generation of adults will emerge in May or early June, to begin the cycle again. - See more at: http://www.emeraldashborer.info/faq.cfm#sthash.LEoBuKpy.dpuf