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ISSUE 2   May 22, 2008


As part of your farmís Insect Resistance Management (IRM) Plan for growing Bt corn, a non-Bt corn refuge is required by the U.S. Environmental Protection Agency. Refuge corn acres are hybrids that do not contain the Bt insect trait. The purpose for planting a corn refuge is to prevent or delay the development of resistance to Bt traits. In return, the sustainability of Bt corn should be improved, so Bt corn is around as a pest management tool against corn insect pests for a long time. Twenty percent of the corn acreage must be planted as a Bt corn refuge on each farm where Bt corn is planted. Remember, itís the law! There are different configurations and distance requirements for planting the refuge depending on the traits. (See following references.)

A new University of Wisconsin Extension publication, Insect Resistance Management and Refuge Requirements for Bt Corn - A3857 (authors Cullen, Proost and Volenberg) answers frequent questions about IRM and the refuge requirements and configurations.

Examples of questions answered by this bulletin include:

What is insect resistance management (IRM)?
Why is IRM important?
What happens if I donít plant a refuge?
Who checks for IRM compliance?
What are the refuge requirements for single Bt trait hybrids with Lepidoptera ("caterpillar") protection?
What are the refuge requirements for single Bt trait hybrids with corn rootworm protection?
What are the refuge requirements for stacked Bt trait hybrids with both Lepidoptera and corn rootworm protection?
How do you select the best Bt insect trait package?
How long will Bt insect traits work?
Where are Bt traits expressed in the corn plant?
What if the Bt corn hybrid is not controlling the targeted insect?

Copies can be ordered from the UW Ext. Learning Store:


Another educational website is the National Corn Growers Association website with their online course on Insect Resistance Management Learning Center:


DTN and the National Corn Growers Association also hosted a free web seminar on Bt corn insect resistance and refuges. The session was designed for corn producers, Extension specialist, county agricultural agents, crop consultants and other educators. The link to see/hear the webinar is:




Last year, the southern half of North Dakota had accumulated enough degree day (DD) units, 300 weevil DDs (base 48 F), to start field scouting for alfalfa weevil activity by May 22, 2007. In contrast, this year the DD accumulations are much lower and range between 100-142 weevil DDs in the southern half (see DD map). Alfalfa weevil infestations have been increasing in incidence and severity over the last several years. However, it is difficult to predict if weevil populations will be higher again this year. Alfalfa weevils overwinter as adults (see photo) in plant debris, woodlots, and ditches. As temperatures warms up adults migrate to alfalfa field to lay eggs.

By using degree days with a base of 48F, the life stages and development of alfalfa weevil can be predicted (see degree day table). Go to the insect section in the NDAWN website:


and select the degree day base of 48F to determine the accumulated degree days for your location. Updates on the weevil DD accumulations will be posted in the next issues of the Crop & Pest Report.

Adult alfalfa weevil
Adult alfalfa weevil (Photo by Clemson Univ. -
USDA Coop. Ext. Slide Series, Bugwood.org)

Degree day map

Stage of Development

Degree Days Required to Complete Indicate Life Stage

Accumulated Degree Days (base 48 )


General Activity




7 to 14


1st instar



21 to 28

Light leaf feeding

2nd instar



Light leaf feeding

3rd instar



Major leaf feeding

4th instar



Major leaf feeding





Mating & egg laying



Lurking in the tall grasses are thousands of ticks waiting for the unsuspecting scout, hiker, gardener, camper, ...! Ticks do not fly or jump, but find their hosts by detecting carbon dioxide and/or vibrations from walking animals. The black-legged tick (deer tick), Ixodes scapularis, is the primary vector of the bacterium Borrelia that is responsible for Lyme disease. Lyme disease occurs in three major regions of the U.S.: Wisconsin to Minnesota, Maryland north to Maine, and California and Oregon. Although it has not been officially recorded in North Dakota, people traveling from nearby infected areas can easily pick up the diseased ticks. Symptoms of Lyme disease are a bullís-eye rash, fever, headaches, and other flu-like symptoms. Only 60% of the people infected actually exhibit a bullís eye rash within two day to four weeks, so do not rely on the presence or absence of such a rash to determine the likelihood of infection. A blood test by your doctor can usually tell if a person is infected. Early treatment is essential to prevent severe and long-lasting symptoms, like arthritis, swelling and pain in joints. Lyme disease also has been diagnosed in pets, especially dogs, and in horses and dairy cattle.

Remove the tick properly. Use a sharp pointed tweezers and grasp the tick close to your skin where the mouthparts are embedded. Pull straight out with a slow, steady motion. The tick should be removed in about 30 seconds of gentle pulling. Do not twist or turn the tick, which may force more of its saliva and guts into your body. Disinfect the general area of bite with antiseptic. Do not apply any substances to the tick before removing it, such as alcohol or nail polish, petroleum jelly or other ointments; or try to burn it with matches. It will just continue to suck your blood and pump more dangerous microbes into your body. Save your tick specimen in a labeled glass jar for identification and testing. The tick in the genus Ixodes are very small about the size of a sesame seed and thus easy to overlook (see photo). It is a common misconception that ticks burrow into the skin. Ticks secrete a whitish cement-like substance around her head and jaws to hold her onto her host. This substances often causes many people to mistakenly believe that the ticks are burrowing into their skin.

Blacklegged tick
Deer ticks (on left) and American
dog ticks (on right)
(Photo by
Jim Occi, BugPics, Bugwood.org)

Reduce your risk to tick bites and their tick-borne diseases. Apply insect repellent frequently with 30%-50% DEET or 7%-15% Picaridin, onto pants or other exposed clothing. Wear light-colored clothing, long-sleeved shirt, long pants and boots. Tuck pant cuffs into socks. And remember to check yourself and your animals frequently when walking in the woods or grasslands. If you have an unexplained illness with rash or fever, call your doctor and be sure to let him know if youíve been in places where you may have picked up an infected tick.

Pesticide control. Insecticides can be applied periodically to reduce overall tick populations. Check insecticide labels for those products that will kill ticks around the yard [sevin (carbaryl), tempo (cyflutrhin)]. READ AND FOLLOW ALL PRECAUTIONS AND DIRECTIONS ON THE INSECTICIDE LABEL.

More information is available on the Center for Disease Control (CDC) website:


Janet Knodel
Extension Entomology

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