Iowa State University Extension and Outreach

East-Central and Southeast Iowa Crop Information


May 17, 2004


Time to Scout for Black Cutworms

Reports of small black cutworms and larger dingy cutworms doing some leaf feeding in the area have been received. Black cutworms do not over winter in Iowa. The moths fly in from the south and if they stay around long enough to lay eggs, young corn plants may be injured. Significant flights occur very regularly, but damage at a treatable level generally occurs less than once per decade. A series of black cutworm moth traps is set up around Iowa and Illinois to monitor moth flights. Significant flights of black cutworm adults (moths) entered Iowa during April 19-21 and were caught in the pheromone traps. From these catches we can predict first cutting of corn. Black cutworms require 300 degree days (base 50F) for larvae to be large enough to cut corn plants (which is about the length of a dime).

Cutting could begin today in SE Iowa (approximately south of Hwy 92) and on May 20 in EC Iowa. It is best to start scouting corn fields a couple of days before the projected cutting date. Because there have been several moth flights since the first ones, continue scouting corn fields until they reach the five-leaf stage (V5). Treatment is generally recommended with 2-3% cut plants when cutworms are about 3/4" long and 5% cut plants with cutworms of 1" or longer. For more information see the May 17 ICM newsletter at



Most of the corn planting has been completed in the area, and in general stands look good. However, every year there are a few problems with poor stands where replant decisions need to be made. The following table summarizes Dale Farnham's research from 1997-2000 and can be used as a guide in making replant decisions

	   ---------------- Planting Date --------------------------------
Stand     April 20 -     May 13 -     May 26 -     June 10 -     June 24 -
X 1,000   May 5          May 19       June 1       June 16       June 28
	    ----------------- (Yield - % of maximum) ---------------------	
28 - 32   100             99           90           68            52
   24      94             93           85           64            49
   20      81             80           73           55            42
   16      74             73           67           50            38
   12      68             67           61           46            35

This table is based on fairly uniform existing stands. The less uniform the stand, the lower the yield. The common way to evaluate corn stands is to count the number of corn plants in 1/1000 of an acre along a corn row at several places within the field. 1/1000 of an acre is

13'9" in 38" rows
14'6" in 36" rows
17'5" in 30" rows
26'2" in 20" rows (or 2 rows 13'1" long)

Adapted full season corn hybrids can be planted until about May 25. If planting is done after this, switch to a hybrid about 5 days earlier in maturity. For more information see the publication "Corn Planting Guide" (Pm-1885) at


Events In the Coming Month to Get On Your Calendar

May 25 Canada Thistle Control in CRP Tour - Keokuk County

  • View 15 different herbicide programs for controlling Canada Thistle
  • Learn of Ways to Increase Plant Diversity and attract wildlife in CRP
  • Free Meal at 600 p.m. followed by Tour Belva Deere Park north of Sigourney in Keokuk County
    From Hwy 149 take 180th Street to 242nd Ave and head south to park.

    June 2 Pasture Walk focusing on Multiflora Rose Control - Iowa County

  • View 14 different herbicide programs for controlling multiflora rose in pasture.
  • Free Meal at 600 p.m. followed by the tour.
    1 mile west of Homestead (Hwy 6 & V Ave) on Amana Farms.

    June 17 SE Iowa Research & Demonstration Farm Spring Field Day Featuring Elwynn Taylor

  • Crop Weather Outlook
  • Relay Intercropping of Soybeans into Wheat
  • Improve Profits with Low Linolenic Soybeans
  • Controlling Weeds in non-GMO Soybeans;
  • Corn Nitrogen Needs in Crop Rotations.
    Tours start at 100 p.m. at the farm located SE of Crawfordsville.
  • A special CCA session will be held in the morning. for details.

    June 24 NE Iowa Spring Field Day, Nashua

  • Lunch and Static Displays 12:00 noon - 1:30 pm
  • Wagon tours from 1:30 pm - 4:30 pm

    June 28 Pasture Walk in Benton County

  • Focus will be on typical creek pasture concerns
  • Meal at 600 p.m.
    Don Newton Farm on the corner 18th Ave. Dr. and 75th St. DR NW of Blairstown.


    If you have any questions, please feel free to contact the Iowa State University Extension Office.
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    Last Update: May 17, 2004
    Contact: Jim Fawcett

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