Iowa State University Extension and Outreach

East-Central and Southeast Iowa Crop Information


May 9, 2006

May 9, 2006




Time to Scout for Black Cutworms


Black cutworm pheromone trap catch data is being reported at:

Based on these traps, scouting for the pest in southeast and east central Iowa would start around May 11, although I’ve received some reports of cutting already. This is an infrequent spotty pest.  Reporting significant flights does not mean that we will have a problem.  The economic threshold is when cutworms average less than 3/4 inch in length and 2-3% of the plants are wilted or cut, or if cutworms are longer than 1 inch, treatment should be applied if 5% of the plants are cut.  For more information, go to the May 1 issue of the ICM Newsletter:


Corn Flea Beetles


The mild temperatures of last winter suggest potential problems with corn flea beetles attacking seedling corn further north than normal.  Monitor corn for this pest from emergence through V5.  See pages 90 – 91 of the April 17, 2006 ICM Newsletter or and pages 63 - 64 of the May 7, 2001 ICM Newsletter or for scouting and management details.


Emergence Problems


In general corn emergence has been good this spring. However, some fields planted in mid-April that were just ready to emerge 2 weeks ago when the cold weather hit had some leafing out underground resulting in somewhat reduced stands. Fields planted a few days later were not affected as much. It is not likely that it will pay to replant stands of 26,000 or more, if the remaining stand is fairly uniform. The uniformity of the stand and replanting costs need to be considered in making decisions on stands of less than 26,000. The following table can help in making replant decisions:

Influence of planting date and plant population on corn grain yields

------------------ Corn Yields (% of maximum) -----------------
Stand     April 20 -     May 13 -     May 26 -     June 10 -     June 24 -
X 1,000   May 5          May 19       June 1        June 16       June 28

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

Numerous gaps of up to 4-6 feet can reduce yields by an additional 5-6%.

For more information, see Pm-1885 "Corn Planting Guide," which is also available at and NCR 344 "Uneven Emergence in Corn" at


Delayed Herbicide Applications


            The recent wet weather has meant that some producers need to change their planned weed control programs because the preemergence herbicides haven’t gotten on. The amide products, such as Dual, Harness, and Outlook, will not control emerged grasses. The premixes containing atrazine, such as Bicep, Harness Xtra, and Guardsman Max, can control small (less than 1”) emerged foxtail, but generally control is lower than the expectations of most producers. After corn has emerged, do not apply herbicides with a UAN solution. See the latest ICM Newsletter for more details at  Postemergence options for grasses include Accent (nicosulfuron), Steadfast (nicosulfuron + rimsulfuron), Resolve (rimsulfuron), and Option (foramsulfuron). In most Iowa corn fields, a one pass herbicide program does not give season long control. For more information on postemergence herbicide options for grass control in corn see




Bean Leaf Beetles


            Bean leaf beetles are showing up in alfalfa fields and early planted soybean fields. The mild winter has likely resulted in greater than normal overwintering of this pest. So, as soybeans emerge, be sure to scout for this insect.  See pages 81 – 82 of the May 27, 2002 ICM Newsletter or for scouting, threshold, and management information.  In addition to the management strategies offered there, remember that Gaucho 480 and Cruiser 5FS seed treatments offer good protection.  Additional information can be found at


Asian Soybean Rust


            No soybean rust has been found yet on soybeans in 2006 in the U.S. All finds so far have been on kudzu, mainly in Florida. No new finds were reported from the first week of March through April, probably because of the dry weather in the south. Recent wetter weather will make conditions more conducive for the disease. For the latest map on soybean rust see




Leaf Diseases in Hail Damaged Fields


            Some fields that received some hail in mid-April are showing an increased incidence of leaf diseases as well as some unusual leaf symptoms such as leaves that are twisted or puckered. Plants may not show obvious hail damage, but plants that were more protected from the hail such as near grass along the edge of the field, will be taller and healthier. The yield of the first cutting will be reduced on these fields, but plants should be fine later in the season unless we have another weather event that leads to increased diseases.


Frost Damage


            Some alfalfa fields showed frost damage after the frost 2 weeks ago. Leaves on the upper half of the canopy may be almost white or translucent. Less damage was evident on clover and grasses in the field.


Alfalfa Weevil


            There have been few reports so far of problems with the alfalfa weevil this spring. For information on scouting for this pest see the April 17, 2006 ICM Newsletter at



If you have any questions, please feel free to contact the Iowa State University Extension Office.

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Last Update: May 9, 2006
Contact: Jim Fawcett

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