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East-Central and Southeast Iowa Crop Information


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CROP UPDATE 5/11/2007

May 11, 2007




Time to Scout for Black Cutworms


There was a sporadic flight of black cutworm moths into southern Iowa on April 3. Based on growing degree days, cutting from that moth flight could be occurring now. Virgil Schmitt received a report this Monday of small black cutworms doing some leaf feeding, which precedes cutting, therefore scouting should be done now in areas south of I-80. A later moth flight occurred on April 23. Cutting from that flight could occur the middle of next week. 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 7 issue of the ICM Newsletter:



Late Planting & Emergence Problems


There are still many acres of corn to plant.  We normally think that the ideal planting time is now at an end.  However, yields generally do not begin to drastically decline until planting is delayed until after May 15 – 20.  It is not necessary to consider switching to a shorter season hybrid until about May 25.


Although corn emergence has been good in most fields, there have been some problems with the first planted corn due to soil crusting and cool temperatures. It is not likely that it will pay to replant stands of 25,000 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 25,000. 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 X 1,000

April 20 – May 5

May 13 – May 19

May 26 – June 1

June 10 – June 16

June 24 – June 28































The table is based on trials done from 1997-2000 in three locations in Iowa.

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” 






Bean Leaf Beetles


The good news is that with the delay in soybean planting, the problems with bean leaf beetles should be reduced this year. The over-wintered beetles are forced to feed on other plants, such as alfalfa and showy tick trefoil. The beetles do not thrive on these alternative food sources and thus do not reproduce as much. The bad news is that for anyone that did get their beans in early, the bean leaf beetles will flock to those fields as soon as they emerge. See pages 81 – 82 of the May 27, 2002 ICM Newsletter or  for scouting, threshold, and management information.





Canada Thistle Control in CRP – 6:30 p.m. May 22 –Swisher


Twelve herbicides programs can be viewed in side-by-side plots one year after they were sprayed on CRP ground on the Wendell Simonson Memorial shotgun range SW of Swisher. A free meal is available at 6:30, followed by the tour. Also discussed on the tour will be controlling other troublesome weeds in CRP, including multiflora rose, and other CRP issues, including the planting of food plots, and CRP mid-contract management. To reach the tour site – take exit 10 from I-380, go west ˝ mile to Hwy 965, then south 2.5 miles to Amana Rd (F-20) and then west 3 miles.


CCA CREDIT OPPORTUNITY – June 21 – SE Iowa Research & Demonstration Farm


Earn 5 CCA credits, including 2 in soil and water management, by attending a special CCA session the morning of June 21, followed by the annual spring field day at the southeast Iowa Research & Demonstration Farm near Crawfordsville. Watch as details emerge.



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

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Last Update: May 11, 2007
Contact: Jim Fawcett

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