SIGNS & SYMPTOMS
Early detection of EAB in newly infested trees can prove very difficult, particularly for the lay property or woodland owner as the trees tend to exhibit few, if any, visible external symptoms of infestation. When EAB infestations begin in an area it can take years for the first trees to die and in these cases EAB is very difficult to detect. The first symptoms to occur are cracks in the bark where the individual EAB have been feeding. As EAB populations build, woodpeckers learn to feed on them and their foraging efforts are easy to detect even from long distances. When trees begin to decline rapidly with further EAB population buildup canopy thinning and epicormic sprouting (water sprouts) become more apparent. D-shaped adult emergence holes are small and hard to detect when there are few, but a reliable sign as populations build.
S- Shaped Larval Galleries and EAB Larvae.
If the bark is removed and frass-filled serpentine, S-shaped galleries are found tunneled just beneath the bark or etched into the underside of the bark, this is a definite sign of EAB infestation [common native borers that infest ash trees bore into the sapwood after feeding a bit in the inner bark].
The presence of white to cream-colored, legless, flattened, 10-segmented, 1 to 1 1/2 inch (25 to 38 mm) long larvae found in the galleries beneath the bark of living ash trees is another definite sign of the presence of emerald ash borers. EAB larvae can separated from other beetle larvae by the "nested bells" look to their body segments.
D-Shaped Emergence Holes.
A clear indication of EAB infestation is the presence of D-shaped holes chewed through the bark on branches or the trunk by adults as they emerge in late-spring. These holes are 1/8 inch (3 mm) in diameter. If the holes are not D-shaped, then they were not caused by EAB (native wood borer emergence holes are round or oval and are generally much larger, 1/4 inch (6 mm) or more). EAB usually starts infesting trees in the mid to upper part of the tree; therefore, in early infestations exit holes can be hard to spot from the ground.
Vertical Splits in the Bark.
Thin, 2 to 5 inch (5 to 12 cm) long vertical splits through the bark of living trees [again, this symptom is not exclusive to EAB infestation]. In the early stages of an infestation trees will be attacked by only a few EAB in a year. The larvae will kill the bark in the area where they are feeding (about the size of your hand) but the surrounding tissue remains healthy. The following year the tree will grow radially and the dead bark above where the EAB was feeding will split. The split will get larger over the next few years and often the larval gallery can be seen beneath the split.
One of the first easily noticeable signs of infestation is often the presence of abundant bark flaking and uneven holes drilled by woodpeckers as they feed on EAB larvae and pupa. Please note that this sign is not applicable where woodpeckers are not abundant such as in industrial areas or city centers. Woodpeckers often scrape off the outer flakes of bark in their foraging area creating a "blonde" patch. This blonding is highly visible from a distance, especially when wet. Although bark can be flaked off ash trees by any number of influences, you can distinguish woodpecker foraging by the little dark holes where they have penetrated the bark to remove an EAB larva.
Epicormic Shoots.Another symptom of a possible EAB infestation (but not limited to EAB) is the sprouting of epicormic shoots around the base of the tree or on the trunk. Epicormic shoots, or water sprouts, are shoots that often appear in trees due to stress or injury (such as defoliation or die-back) as a way for the tree to compensate for the loss of productive leaf surface.
Thinning Canopy.As the density of EAB infestation in an ash tree increases, the tree's canopy will begin to thin out. In the early stages of canopy decline thinning is primarily due to a decrease in leaflet size because the resources needed to produce large leaves are being consumed by EAB. As the crown continues to deteriorate whole branches will begin to die off. When EAB first reaches an area it may take 5 years or more for trees to begin showing canopy symptoms. However, trees may die after only 2 to 3 years in areas of heavy infestation.
Many symptoms of an Emerald Ash Borer infestation can be similar to symptoms caused by other insect pests or diseases. Look for a combination of symptoms and signs when trying to determine if your trees may be infested with EAB.