Emerald Ash Borer FAQs

How is the emerald ash borer spread?

The most common way for the emerald ash borer to spread is through people moving infested materials such as firewood, logs, branches, nursery stock, chips or other ash wood. The emerald ash borer also spreads naturally through beetle flight. Research indicates the adult can fly up to 10 kilometres, but generally does not stray from the immediate area when it emerges.

What kinds of trees are affected by the EAB?

In North America, the emerald ash borer has been found to attack and kill all North American species of ash (Fraxinus spp.). The mountain ash (Sorbus spp.) is not related to ash trees and the insect does not attack that tree. Infested ash trees generally die after two to three years, but heavily infested trees have been observed to die after only one year of beetle attack.

Does it only attack dying or stressed trees?

Healthy ash trees are also susceptible, although beetles may prefer to lay eggs or feed on stressed trees. When EAB populations are high, small trees may die within 1-2 years of becoming infested and large trees can be killed in 3-4 years. EAB attacks ash trees of all sizes from 1 cm in diameter and larger

How does EAB kill ash trees?

Its larvae bore tunnels under the bark to feed on inner bark tissue. The tunnels cut the flow of nutrients and water to leaves, causing the tree to die.

How much damage can the EAB cause to trees?

Tree mortality will result if a tree has been infested with EAB. Mortality may occur in as short a period as one year, however, death normally occurs within 2-3 years of a tree becoming infested.

What is the importance of ash trees?

Ash trees are an important part of Canada’s urban and rural landscape. They are commonly found on city streets, in woodlots, in windbreaks and in forests across southern Canada. In many areas of western Canada, ash trees are one of the few suitable for planting in urban areas.

Ash wood is also used to make furniture, hardwood floors, baseball bats, tool handles, electric guitars, hockey sticks and other materials that require high strength and resilience.

How can I tell if I have an ash tree on or near my property?

Ash have a characteristic pattern of branches that is similar to maple in that the twigs emerge from the branch opposite to one another. Most other tree species in Ontario have an alternate pattern of branches.

Ash trees can grow to 30 meters (m) in height and are a common species in the urban forest. Ash have a compound leaf 13 to 30 centimeters (cm) in length. A compound leaf has more than one leaflet on its stalk base. Ash trees have five to nine leaflets per leaf depending on the species.

The bark on young trees and younger branches tends to be smooth and grey although it sometimes appears reddish on some species. Over time, the bark becomes rougher and forms ridges and furrows. Some older ash trees have a characteristic diamond pattern to their bark.

How can I tell if an ash tree is infested by EAB?

Unfortunately, this is extremely difficult. Without cutting the tree down and skinning off most of the bark, it can be difficult to determine whether a tree is infested. A lot of the symptoms associated with EAB, such as shoots (suckers), cracking bark, D-shaped holes and thinning crowns only become evident after two or more years of infestation. One or more of these symptoms may appear even without the presence of EAB.

Signs of EAB infestation include: yellowing foliage, thinning tree crowns and dead branches. Heavy seed production may also be seen near the end of the tree’s life, as trees can produce a heavy seed crop in reaction to stress. You may also see on the tree bark splitting or discolouration and characteristic D-shaped exit holes that are about 3 mm in diameter. New shoots may be seen sprouting from various places on the trunk as the tree dies.

EAB symptoms may not show up for 2 or 3 years after the tree has been infested.

Woodpeckers feeding on EAB larvae and the resultant damage to the bark, may be seen on the tree as well. Eventually, the bark from a dead tree will begin to peel away exposing the larval galleries beneath. For more information, see Canadian Forest Service – A Visual Guide to Detecting Emerald Ash Borer Damage (PDF).

How severe will the infestation be?/ How serious a threat is the emerald ash borer?

Thus far, infestations elsewhere in North America have increased and spread despite significant control measures attempted. Once established, EAB has proven impossible to control. Once established, adult EAB can disperse to distances of several kilometres by flight.

During the relatively short time that the emerald ash borer has been in North America, it is believed to have killed millions of trees in the United States and Canada, with billions more across North America at risk of infestation and death.

What are the environmental impacts that will result from an infestation of EAB?

Ash forests provide habitat for numerous animals and birds and are integral to the health of soils and watersheds. In natural forests of southern Ontario, ash trees generally form a high proportion of the young tree population. The loss of ash trees will reduce or eliminate food and shelter sources for wildlife, thereby disrupting the ecology of tableland and valleyland forests. Ash trees are also valued as a street tree, being relatively fast growing and one of the very few species that are tolerant of difficult growing conditions typical in urban areas. The loss of the ash species will limit diversity of the future urban forest. All species of ash play an important role in maintaining the health of the environment in which they are located.

How many trees could be affected by EAB?

City of Toronto: All ash trees in Toronto are at risk from this infestation. It is estimated that Toronto has an ash street tree population of 32,400 trees. The recent canopy study estimates that there are 860,000 ash trees in total on public and private lands. The initial areas of infestation that are detected in 2007 are likely to lose most ash trees by 2015. EAB will spread to the rest of Toronto, killing most ash by about 2015 – 2017.

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