Iowa State University Extension and Outreach

East-Central and Southeast Iowa Crop Information



May 16, 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 will achieve 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.

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 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.

For scouting, threshold, and management information, see 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.


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


If you have any questions, please feel free to contact the Iowa State University Extension Office.
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Last Update: May 16, 2005
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