PRAIRIE GARDENER: Ash-loving insect boring into Minnesota

ITASCA STATE PARK, Minn. -- If you toured this wonderful state park -- Minnesota's crown jewel -- last summer, you probably noticed purple tent-like devices scattered in areas of the facility.

Darrel Koehler
Darrel Koehler

ITASCA STATE PARK, Minn. -- If you toured this wonderful state park -- Minnesota's crown jewel -- last summer, you probably noticed purple tent-like devices scattered in areas of the facility.

What you actually saw were three-cornered purple prisms used to detect emerald ash borers. This was an effort by the Minnesota Department of Agriculture to track down and head off the destructive, invasive pest. The department will hang out about 6,500 of these traps in trees around the state beginning this month. This number of traps will be about 2,000 more than in 2011.

The purple traps will be placed on ash trees that have been baited with a lure that will attract the borers. The insects believe they have found a stressed ash tree. A sticky layer on the outside will hold the insect until workers can return for a check.

The traps aren't designed to destroy swarms of the pests, but rather determine the extent of the range of the borers as they continue to spread throughout the Gopher state. Visitors to state parks, such as Itasca, are urged not to disturb the traps so an accurate determination can be made.

The traps will not be placed in four Minnesota counties under quarantine: Hennepin, Ramsey, Houston and Winona. Emerald ash borers already have been discovered in these counties.



According to the U.S. Department of Agriculture, the emerald ash borer probably arrived in this country first in Detroit. The pests came ashore in shipping material from China. Scientists believe the beetle may have been present for up to 12 years before it was detected, based on widespread distribution and destruction. It was officially identified in this country in 2002.

Today, the beetles can be found across 15 states and in Quebec and Ontario in Canada. Devastation elsewhere has left Minnesota with the most ash trees of any state in the union -- nearly 1 billion. They comprise about 7 percent of the trees in Minnesota forests and 15 percent of the trees in cities. Ash varieties include green, white and black. They were a popular replacement for elm trees that were destroy by Dutch elm disease two decades ago.

Ash borers first were detected in Minnesota near Hampden Park in St. Paul. They have since spread to other areas in St. Paul and elsewhere. Another outbreak was reported in the La Crosse, Wis., area, with the borers spreading across the Mississippi into Houston and Winona counties. So far, the remainder of Minnesota has been spared including the northwestern corner as well as northeastern North Dakota.

Life cycle

Emerald ash borers have a quick life cycle. The adult ash beetles lay eggs in ash trees.

The eggs develop into larvae, which drill into tree and grow under the bark, usually emerging as adults the following spring, which is when they are detected. Native ash trees have no resistance to ash borers as do the ash trees in Asia. One variety, Mancana, is said to have some resistance. Check with your garden center. Scientists are releasing several species of predatory wasps from Asia to contain the spread of the borers, but it is expected to take years before they reach a balance with the ash borers.

The biggest spread of the disease is the movement of wood products made from ash, especially firewood. The beetles can easily hitch a ride, spreading the disease far from the original site. Purchase firewood at the camp site and use it or leave it on site. Don't take it home.


While it may be years before the beetles will arrive in this region, there are federally-approved insecticides that you can have applied. Options include systemic and topical insecticides. These compounds need to be applied on a regular basis, possibly several times in one growing season, and even that might not completely prevent the dreaded beetles from attacking the tree. Even treated trees are likely to succumb to continued attacks from the pest as the beetle population increases. Treatment is also costly.

New elm variety

While the news isn't exactly as rosy for the ash tree, it is better for the elm. Thanks to plant breeders, the Princeton variety is now available to gardeners. This elm variety is highly resistant to Dutch elm disease, heralding the return of the American elm. It is completely winter hardy, grows quickly and has a butter-yellow fall color. It was chosen to line Pennsylvania Avenue near the White House in Washington D.C. Tree supplies may be limited.

Early bloomer

The yellow forsythia has put on quite a show in Grand Forks. There are about six large bushes just south of the bus transit center, They provide cover from the railroad tracks that separate the courthouse and transit center. These are eventually very hardy forsythia as older varieties would lose their flower buds if temperatures dropped to low. In that case, they would only bloom on the lower branches, which had been covered by snow. The variety Meadowlark would be one to consider for your yard. You will not find an earlier blooming shrub in this region than forsythia, which can also be forced into even earlier bloom indoors.

Garden dates

After a successful "Gardening Saturday" event in mid-April, the Grand Forks Horticulture Club is preparing for its annual garden tour, which is scheduled for July 21-22. Debra Hopkins will be taking over the reins from Zona Pearson, longtime coordinator, who stepped down in 2011. Hopkins said the tour will be similar to other recent ones with events originating at the Myra Museum. More information will be provided later, but circle those dates on your calendar.

The 89th annual conference of the North Dakota State Horticultural Society will be July 26 to 28 in Bismarck. For information, write Jackie Buckley, Morton County Extension Office, 210 Second Ave. N.W., Mandan ND 58554. Keynote speaker will be Eric Bergeson, newspaper columnist, speaker and owner of Bergeson Nursery in Fertile, Minn.


Today is Earth Day so enjoy. This date has been observed since the late 1960s.

Koehler is the Herald's garden columnist. Send garden questions to him in care of the Grand Forks Herald, Box 6008, Grand Forks ND 58206-6008.

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