Monday, September 7, 2015

Emerald Ash Borer Update

Emerald ash borer - Leah Bauer USDA Bugwood
Emerald ash borer (EAB) has been cropping up in new locations across Missouri as seen in the map below. You may recall from a previous blog or other publications, this is a serious threat to our ash trees, capable of nearly wiping out the species similar to the attack of Dutch elm disease in past decades. It is spread by moving wood such as firewood into unaffected areas.
First found in the US in 2002, the EAB, Agrilus planipennis, is naturally found extending from eastern Russia to China and Japan. It likely arrived in shipping materials and first was found in Michigan. With time it has spread through the eastern US.
The tiny beetle itself is rather beautiful although seldom seen. After emerging, it nibbles a few ash leaves for a week, mates and then lays 40-200 eggs in ash bark crevices and cracks. When the larvae emerge they chew their way under the bark, tunneling into the tree's underlying circulatory system. The larva will go through 4 stages (instars) over weeks before pupating. When the adult beetle emerges, usually in the spring, it chews a characteristic D-shaped hole and then flies up into the tree to start the cycle again.

Larval Tunnels - USDA
The larval tunnels in the cambium under the bark gradually disrupt the vascular system, blocking the flow of phloem (delivering photosynthesis-derived nutrition from the leaves to the rest of the tree) and xylem (carrying water and minerals upward from the roots). The tree slowly dies from the top down.

Prevention is the best answer by not transporting infected ash wood, usually as firewood carried by unsuspecting campers. There are treatments for individual urban trees but none for our forests in general. MDC has published a new four-page guide called the Emerald Ash Borer Management Guide for Missouri Homeowners. The guide can be found at this link.

Comprehensive current information is on this Wikipedia site.

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