May 7, 2009 at 9:16 a.m.
Johnson reported that the average life of avenue trees in the suburbs is 35 years. One would think that the reason would be due to chemicals, acid rain and other pollutants. However, the main reason is because trees are planted too deep. Trees planted from pots with the roots wrapped around the trunk tend to girdle or strangle the tree. Trees that snap off at the soil line during strong winds are suffering from improper planting.
Johnson called Dutch elm disease and oak wilt, Angels of Death. These diseases go through species of trees with a vengeance with little means of control. He claimed that the next new Angel of Death would attack ash trees. Since more than one fourth of our trees are ash, there was a real concern. The culprit was new to the United States and was called the emerald ash borer. It was first detected in May 2002 in southeast Michigan and could have been in the state for as long as five years.
Houston County, Minnesota, about 30 miles from LaCrosse, Wisconsin, is where the latest Angel of Death has invaded ash trees. Minnesota has 900 million ash trees. The second highest number in the nation after Maine.
This borer belongs to the metallic wood boring beetle group. It is closely related to other metallic wood boring beetles in MN including the bronze birch borer and the two lined chestnut borer. Emerald ash borers are a little larger and brighter than these species. These slender beetles range in size from about one-third inch to one-half inch long and are a bright iridescent coppery green.
This beetle is a native of Asia and the only known host of this insect is the ash tree. In the U.S. the borer has been found attacking green, white, and black ash.
Adult beetles begin to emerge in mid to late May until late June. Females lay eggs on the surface of the bark or in small cracks in the bark and the eggs will hatch in seven to ten days. The whitish flathead borers tunnel into the cambial layer and create a series of winding crisscrossing galleries under the bark in the phloem and outer sapwood. They feed until fall and then over winter as fully-grown larvae. They pupate the following spring and adults emerge in May and June.
The emerald ash borer commonly attacks unhealthy and stressed trees. However, unlike other insects, the ash borer apparently will also attack vigorously growing trees of any size.
To reduce the risk of spreading, Minnesota officials have encouraged citizens to use only local firewood. States with infestations have also established quarantines, which prohibit taking ash firewood, timber, mulch, pallets, or nursery stock that might contain beetles out of the county.
Quarantine is a possibility in southeastern Minnesota depending on whether the beetle turns up. Since beetles are not active until May, inspectors are looking for such evidence of dead branches, loose bark, and serpentine tunnels packed with sawdust under the bark.
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