Iowa State University Extension and Outreach

East-Central and Southeast Iowa Crop Information


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May 22, 2007

May 22, 2007




Continue Scouting for Black Cutworms


I found 0.5% cutting in a field just south of Iowa City. Cutworms in the field were only 0.5” long last week, but were over an inch long yesterday, so seem to be growing rapidly with this warm weather. 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:


Nitrogen Losses

With the warm fall and early winter followed by generally abundant rainfall this early spring, many are asking, “How much of the nitrogen applied last fall was lost?”  The following articles can help answer questions regarding nitrogen loss:

Nitrogen loss: How does it happen?
Estimating nitrogen losses – early spring 2007
Measuring the nitrogen status – 2007
Corn response to supplemental nitrogen


  Use of the late spring soil nitrate test may help answer the question.

Late Spring Soil Nitrate Test

We are approaching the time to be pulling soil samples for the late spring soil nitrate test. Soil samples should be pulled to a one foot depth when the corn is 6-12” tall. It is best to use a systematic method rather than a random method to pull the samples. Pull the first sample in the corn row, the next 1/8 of the distance between rows, the next ¼ the distance between rows, etc. until you have worked your way across the rows. Do this at least twice for a total of 16 cores. This way you won’t by chance happen to be over or under representing areas that have higher bands of nitrogen (ie anhydrous bands, manure bands, starter fertilizer). Soil samples should be sent to a lab immediately after sampling. Results can help to fine-tune nitrogen management. For more details see the publication “Nitrogen Fertilizer Recommendations for Corn in Iowa” at for more details.





Bean Leaf Beetles


Bean leaf beetles have been thick on early emerged soybeans. Usually the damage from the over-wintered  population doesn’t justify the cost of an insecticide treatment, but with the higher soybean prices, the economic threshold is lower (about 2-3 beetles per plant soon after emergence). The beetles need to be controlled immediately after soybean emergence to help prevent bean pod mottle virus, which is especially important with seed beans.  See pages 81 – 82 of the May 27, 2002 ICM Newsletter or  for scouting, threshold, and management information.



To Cut or Not to Cut?

There is an ongoing debate about whether or not hay should be cut at the normal calendar date, given the stress placed on the crop as a result of the cold weather in April.  Unfortunately, there is not a clear answer. For producers who do not have dairy, the priority is most likely stand longevity.  These producers should probably cut the hay a week or two later than normal.  This will allow the plants to more fully recover before the first cutting is made.  Subsequent cuttings will be pushed back on the calendar, which may pose complications in the fall as we do not want to cut hay between the first week in September and the last week of October in order to, again, promote stand longevity.

For producers whose priority is high quality (dairy) forage, the crop needs to be made on time because quality declines with time.  These producers will need to “take their lumps” in terms of stand longevity.

Complicating the issue is that some fields are experiencing extensive leaf disease injury.  Normally the recommendation for those fields would be to cut early to retain as much of the leafy material as possible.  However, because of the stress of April, producers who are more concerned with stand longevity than with first-cutting hay quality may opt to not follow the normal recommendation and harvest later instead.


Weed Control in Pastures & CRP


In the next week or so is the best time to spray for Canada thistle. I’ve had the best results when the thistles are sprayed in late May, right before the plants start to bud. Products containing picloram (Tordon 22K and Grazon P + D), clopyralid (Stinger or Curtail), or the new products of Milestone and Forefront, have given the best long term control.




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 ½ 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 22, 2007
Contact: Jim Fawcett

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