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East-Central and Southeast Iowa Crop Information

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May 27, 2008

PONDS AND FLOODED FIELDS

 

With the recent/current rains and related flooding, many are asking the question, "How long can crops be under water and survive?"  Corn and soybeans can normally only survive complete submersion for 2 to 3 days (80 day air temperature) and most forages can survive for 1 - 2 days.  I have seen survival for considerably longer periods of submersion, however.  The cooler the air temperature, the longer the plants can survive.  Plants NOT totally submerged will survive considerably longer.  By the time the water has receded and the field dries out, it will be easy to see whether the crop has survived or not.

 

A light rain shortly after the water recedes / drains might be beneficial to wash off the mud on plants.

 

Flooding can lead to greater disease problems on all crops.

 

Some low-lying fields have had new depositions of soil on top of planted ground.  Corn and soybeans that had emerged will be lost.  Corn and soybeans that had not yet emerged can still come up from greater depths, especially corn.  The limit from which corn can emerge is depths of 4 – 5 inches.  Soybean, because the plant must push the seed up to the surface, is less capable of emerging from greater depths.  A University of Illinois study of relative emergence of soybeans planted at different depths found :

 

Planting Depth

Relative Emergence (per cent of the best)

0.75 inch

85.5

1.0 inch

100

1.5 inches

99.5

2.5 inches

55.2

 

To help you see the impact of partial stands and the potential of re-planted corn, see the May 19, 2008 Crop Update.

 

Soybean is less sensitive to population than corn.

 

Effect of plant density on soybean yield.

(Plants thinned at VCa)

Plants/acre

Bushels/acreb

150,000 (no thinning)

45.1

125,000

44.8

100,000

45.1

75,000

44.2

50,000

41.6

1-ft gapsc (75,000)

43.6

2-ft gaps (75,000)

41.5

a VC, cotyledon stage.

b LSD (0.05) = 2.1 bushels/acre difference between any two means.

c 1- and 2-foot within row gaps were applied 2–4 weeks after planting

Source: University of Minnesota.

 

For your reference, the effect of planting date on soybean yield is shown below.

 

Effect of planting date on soybean yield in Iowa (1995 to 1997).

Planting Date

Northern Iowa

Central Iowa

Southern Iowa

Relative yield (percent of potential yield)

Late April

100*

96*

98*

Early May

96*

100*

100*

Mid-May

99*

96*

98*

Early June

81

93

89

Mid-June

61

59

82

Early July

33

45

47

* Not statistically different from 100 percent.

Source:  Iowa State University Extension publication PM-1851 “Soybean Replant Decisions”

 

If a replant is going to be done and it will be to a crop different from the one originally planted, remember rotational restrictions from any herbicides applied.

 

 

CORN

Fields yet to be planted or re-planted

 

For fields that have yet to be planted or must be re-planted, we have now arrived at the time to consider changing to an earlier maturing hybrid.  On page 3 of Iowa State University Extension publication PM-1885 “Corn Planting Guide,” you will find that “A rule of thumb for changing hybrid maturities is if planting is delayed until May 25, select a hybrid that matures five days earlier than an adapted full season hybrid for that area. If planting is delayed another seven to ten days beyond that, select a hybrid that matures another five days earlier than the previous one.”

 

Black Cutworm

 

I am receiving scattered reports of corn fields that have black cutworm damage above threshold.  Continue to scout all corn for black cutworm until it reaches growth stage V5.  See the May 19, 2008 Crop Update.

 

 

FOR YOUR CALENDAR

 

SPRING FIELD DAY & SPECIAL SESSION FOR CCAs

SE IA RESEARCH FARM – CRAWFORDSVILLE

JUNE 26

 

  9:00 a.m.  – Certified Crop Advisors’ Training

10:30 a.m.  – Drainage Field Day

Noon          – Lunch Available

 1:00 p.m.   – Spring Field Day

 

Certified Crop Advisors can obtain 5 hours of credit (including 2 hours of soil and water) by attending a special session in the morning followed by the afternoon tour at the ISU SE Iowa Research & Demonstration Farm near Crawfordsville on June 26. This will include a tour in the morning featuring the soil drainage research on the farm.  More details will be posted soon.

 

If you have any questions, please feel free to contact the Iowa State University Extension Office.
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Last Update: May 27, 2008
Contact: Virgil Schmitt vschmitt@iastate.edu


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