Ash Trees

Ash Trees

Mountain Ash
The picture to the left is of a mountain ash and is from John Fech, Nebraska Extension in Douglas/Sarpy County.

Typically the plant of the month article is about a plant we desire in our landscapes, however for July, the plant of the month will be about a plant we don’t want in our landscapes but need to know how to identify it for pest management purposes, ash trees. As Emerald Ash Borer has recently moved into Nebraska this year, many people are concerned and the first step in management is to identify ash trees present in your landscape.

Ash tree
The photos in the above collage of ash tree attributes is from the Nebraska Forest Service.

Ash, Fraxinus sp., is a large tree, growing 40-80 feet tall depending on species. Most commonly in Nebraska we plant green ash and white ash. Autumn Purple Ash is a cultivar of the white ash and is commonly planted in landscapes for the reddish purple color in the fall. Ash trees have opposite, compound leaves with 5-11 leaflets per leaf. The branches, buds and leaves grow directly across from each other. The bark is smooth on young ash trees and develops into a diamond-shaped pattern as the trees age. The seeds of ash trees are 1-2 inches long, paddle-shaped and colored green in summer, tan in fall when mature. The seeds are held onto the tree throughout the fall and winter months.

White and green ash should not be confused with mountain ash, which is not a true ash from the Fraxinus genus, and not susceptible to the emerald ash borer. Mountain ash trees have pinnately compound leaves similar to ash, but have alternate arrangement of stems. 

A good way to start the identification process for ash trees is to use the acronym MadBuck. Most of the trees found in North America with opposite branching would include Maples, Ash, Dogwood, and Buckeye. So if you see a tree with opposite branching you have it narrowed down to one of the 4 tree families listed in the acronym.

Another thing to help with identification of Ash trees would include the ash flower gall. Many of our ash trees have ash flower gall, which is not damaging to the tree. This is a distortion to the flowers caused by a mite. The galls harden and turn brown by fall and typically stay on the tree throughout the winter. If you see these galls that just look like distorted flowers you will know you have an ash tree from this as well.

Emerald Ash Borer (EAB) is an invasive insect pest from Asia. This insect pest has recently been found in Nebraska, in both Omaha and Greenwood. EAB is a voracious pest that feeds through the cambium layer of our ash trees to eventually kill the tree. As an invasive pest there are no natural predators here to control it and it feeds on healthy trees whereas our native borers will feed only on stressed or dying trees. EAB only affects ash trees. It will affect all ash trees, but not mountain-ash which is not a true Fraxinus ash tree. EAB is difficult to control, but there are pesticides to help combat it once it is found within 15 miles of your tree. For more information on management and identification of Emerald Ash Borer, visit: http://nfs.unl.edu/nebraska-eab

For July, the plant of the month is here to help you identify the ash trees found in your landscape to help with control of Emerald Ash Borer. Take the time now to go out and determine which trees on your property are ash trees. Then you can start deciding which trees you will treat. Only trees that are in good health, good location, and have a high desirability in your landscape should be treated. If it doesn’t meet these standards, you can start a new tree in your landscape now to replace the ash once it needs to be taken down due to infestation from Emerald Ash Borer.

Nicole Stoner
Nicole Stoner
Extension Educator - Horticulture

As a professional horticulturist, Nicole's focus areas include trees, shrubs, lawns, gardens, and insects.

Gage County Extension
1115 West Scott
Beatrice, NE
68310-3514
402-223-1384

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