Iowa State University Extension and Outreach

East-Central and Southeast Iowa Crop Information


May 18, 2005

May 18, 2005


Black Cutworms

The number of black cutworm moths captured in black cutworm moth traps this spring has been generally low.  To view the numbers, go to A significant catch is considered to be eight or more over two consecutive nights.  It is important to remember that catching moths only indicates they were there; it does not mean they stayed long enough to lay eggs or that survival will be great enough to cause a problem.  However, if there are eight or more caught, there may be enough eggs laid to cause a problem.  By knowing when the moths arrived and by monitoring temperatures, we can fairly accurately predict when cutting will start if eggs were laid and larvae survived.

Three traps in southern Iowa, including the trap at Fruitland / Muscatine, had significant catches in the April 11-12 time frame.  Otherwise, the few significant catches there were generally began in the April 18 - 22 time frame.

If you work off the Fruitland / Muscatine site flight on April 12, we achieved 300 Growing Degree days (GDD) base 50 since the moth flight on Tuesday, May 17.  If you work off the April 18 - 22 flights and assume normal temperatures, we will achieve 300 GDD about:

May 22 +/- one day along Highway 34
May 24 +/- one day along Interstate 80
May 25 +/- one day along Highway 30, and
May 29 +/- one day near Dubuque.

Cooler than normal temperatures will push the dates back while warmer than normal temperatures will move the dates forward.

Remember, it is wise to begin scouting for this pest a couple of days before cutting is predicted to start. A small amount of cutting by black cutworms has already been observed in Benton and Cedar counties, so there was likely an earlier moth flight that bypassed the traps.

Preliminary data from Iowa State University suggests that the low rates of seed-applied insecticides (Cruiser, Poncho) are not effective in managing black cutworms; see or page 76 of the May 9, 2005 ICM Newsletter.  Cruiser was not tested at the high rate, but Poncho 1250 was effective in controlling black cutworms.

Granular insecticides claiming black cutworm control are not always effective.

So it is wise to scout all corn fields for black cutworm injury until the corn reaches the five-leaf stage, when it is too large to be significantly damaged by black cutworms.

When cutworms average less than 0.75 inch in length, an insecticide should be considered if 2 or 3 percent of the plants are wilted or cut. If cutworms are longer than 1 inch, treatment should be applied if 5 percent of the plants are cut. If the field has a poor plant population, 20,000 or less, these thresholds should be lowered.

An article on scouting for black cutworms will appear in a few days at

Also, watch for updated information on the development of this and other insects during 2005.


Flea Beetles

A moderate population of flea beetles was observed in an early planted corn field in Keokuk County. The corn seed had been treated with an insecticide. The low rates of the seed insecticides may not give adequate protection against flea beetles. Flea beetles transmit the virus that caused Stewart's Disease, which is of special concern in seed fields. The following thresholds are used for flea beetle control: in field corn prior to stage V5, 50 percent of plants with severe feeding injury and 5 or more beetles per plant; in seed corn on susceptible inbreds, 10 percent of the plants with severe feeding injury and 2 or more beetles per plant. For more information see the April 29, 2002 ICM Newsletter at .


Alfalfa Weevil

Although alfalfa weevil numbers have generally been well below threshold, continue to monitor alfalfa fields.  Scouting, threshold, and management information is on pages 48 - 49 of the April 11, 2005 Integrated Crop Management (ICM) Newsletter. Also, watch for updated information on the development of this and other insects during 2005.



Despite extensive scouting, there still have been no reports of Asian soybean rust on soybeans or kudzu outside of Florida and Seminole County, Georgia. This makes it increasingly less likely that we will experience a "worst-case scenario" epidemic in the midwest. More information can be found in the last ICM Newsletter at or you can monitor the progress of the disease incidence at



SE Iowa Research & Demonstration Farm Spring Field Day - June 23 1:00 p.m.

 "Asian Soybean Rust Outlook", by Alison Robertson and X.B. Yang, will be the featured presentation at the annual spring field day tour at the Crawfordsville Research Farm. Also featured on the tour will be "Tile Drainage on SE Iowa Soils", by Greg Brenneman, ISU Extension Ag Engineer; "Vertical Tillage Results, Soil Conservation Progress and Rewards in Iowa, & Crop Season Review", by Bruce Trautman, NRCS Area Conservationist & Kevin Van Dee, ISU Farm Superintendent; and a choice between "Soybean Aphids - Will They Be Back?", by Matt O'Neal, ISU Entomologist, or "Is Grape Production For You?", by Patrick O'Malley, ISU Extension Horticulturist.


Brush up on Your Soybean Disease Identification Skills and Earn CCA Credits - Crawfordsville - June 23

Other foliar soybean diseases will be showing up in June, regardless of whether soybean rust makes its way to Iowa. Can you tell the difference? Certified crop advisors can earn 5 CCA credits by attending a special CCA session in the morning of June 23 followed by the SE Iowa Research & Demonstration Farm Spring Field Day Tour in the afternoon. The morning session will focus on Foliar Soybean Disease Identification and will also feature a presentation on soil & water conservation. This would be a good review for soybean rust first detectors. The session starts at 9:30 a.m. If you are not a first detector and wish to become one you need to show up a half hour early (9:00 a.m.). By attending the morning session and the afternoon field day tour you can earn 3 hours in pest management and 2 hours in soil & water management. There is a $50 fee, which includes lunch. If you plan to attend, please send me an e-mail note by June 21 (you can pay at the door). The fee is $70 for those not registered by June 21.


If you have any questions, please feel free to contact the Iowa State University Extension Office.
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Last Update: May 18, 2005
Contact: Jim Fawcett

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