Iowa State University Extension and Outreach

East-Central and Southeast Iowa Crop Information

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May 21, 2013

 
CORN
 

Stands

 

Most of the early-planted corn appears to be emerging well, but there have been scattered reports of stands that are less than hoped for. Some of the corn planted several days before the ground cooled experiencing “cork-screwing” as it attempts to emerge, as well as some seeds that swelled but didn’t germinate. There is also some pythium damping off occurring. It would take stands of less than 20,000 plants per acre to justify replanting now, and in another week or so, stands would need to be less than 10,000 to 15,000. You can use the following table to help to make decisions on re-planting corn:

 

 

Planting Date

Population
(Plants/Acre)

April 20-May 5

May 5-May 15

May 15-May 25

May 25-June 5

June 5-June 15

Percent Maximum Yield

45,000

97

93

85

68

52

40,000

99

95

86

69

53

35,000

100

96

87

70

54

30,000

99

95

86

69

53

25,000

95

91

83

67

51

20,000

89

85

77

63

48

15,000

81

78

71

57

44

10,000

71

68

62

50

38

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

 

This table comes from Roger Elmore’s article at http://www.agronext.iastate.edu/corn/production/management/planting/replanting.html.

 

When do You Switch Varieties?

 

A general rule is that if planting is delayed until May 25, you should select a hybrid that matures five days earlier than an adapted full-season hybrid for that area. If planting is delayed another seven days, select a hybrid that matures another five days earlier than the previous one. In general, the date to switch maturities is later in southern Iowa.

 

Black Cutworms

 

Black cutworms do not overwinter in Iowa. Rather, moths fly in from the south and lay eggs. There have been a few significant moth flights and cutting may soon begin. Significant moth flights are quite common but there are infrequently problems with cutting, so a significant moth flight does not mean there will be much cutting. There is a network of black cutworm moth traps across the state, and with the knowledge of when significant flights occur and by using daily temperatures to calculate Growing Degree Days Base 51 since the flight, we can predict fairly closely when cutting may begin, if indeed it does. Some seed treatments and Bt genetics can help protect against black cutworms, but you shouldn’t assume that they will provide complete protection. Based the growing degree units accumulated since the moth captures, cutting may begin on May 26 in SE & NE Iowa and on May 28 in EC.  Start scouting a few days before this. Information can be found at http://www.extension.iastate.edu/CropNews/2013/0517sissonjessehodgson.htm and http://www.extension.iastate.edu/Pages/eccrops/blackcutworm.html.

 

 

WEEDS

 

Soil-Residual Herbicides Applied to Emerged Corn

 

Can you apply soil residual herbicides over the top of emerged corn?  It depends.  Dr. Aaron Hager, University of Illinois, says “Many, but not all, soil residual herbicides can be applied after corn has emerged.  Products such as Balance Pro, Fierce, Prequel, Sharpen and Verdict must be applied before corn begins to emerge; applications of these products to emerged corn can result in significant corn injury.  Be cautious about applying a soil-residual herbicide in UAN carrier if corn has emerged as this can increase the potential for corn injury.”  See the rest of the article at:  http://bulletin.ipm.illinois.edu/?p=626

 

UAN and Herbicides on Emerged Corn

 

With our weather problems, some fields may be planted before nitrogen and/or pre-emergence herbicides are applied.  While UAN and many pre-emergence products can be applied to emerged corn, Dr. Hartzler points out that using UAN as a herbicide carrier enhances the foliar activity of products and may result in foliar damage.   To read more about this issue go to Bob’s article at:  http://www.extension.iastate.edu/CropNews/2013/0513hartzlersawyer.htm

 

 

FOR YOUR CALENDAR

June 6, 2013

9:00 a.m to 3:30 p.m.

 

Cover Crops Field Day – Coe College - Cedar Rapids

 

Free program, lunch and transportation to field demonstrations are on your own.  Topics include designing cover crop mixes, cover crop management systems, soil function demonstrations, and field demonstrations.  Learn how diverse cover crop mixes can boost your soil health from Ohio Farmer Dave Brandt and NRCS Agronomist Ray Archuleta.  For more information, contact Rick Bednarek, 515-284-4135.

 

June 26, 2013, 1:00 p.m.

 

ISU NE Research & Demonstration Farm Spring Field Day – Nashua

 

As details become available, they will be posted at http://www.extension.iastate.edu/Pages/eccrops/meetnerf.html.

 

June 27, 2013

Special Session for Certified Crop Advisors (9:00 a.m.) &

ISU SE Research & Demonstration Farm Spring Field Day (1:00 p.m.)

Crawfordsville

 

As details become available, they will be posted at http://www.extension.iastate.edu/Pages/eccrops/meetserc.html.

 

 

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

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Last Update: May 21, 2013
Contact: Jim Fawcett fawcett@iastate.edu


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