Iowa State University Extension and Outreach

East-Central and Southeast Iowa Crop Information


August 5, 2005

August 5, 2005



The cooler temperatures will provide some relief for the crops, but, unfortunately, most got little rainfall.  Although corn pollinated well in many fields, some kernel abortion has occurred causing tips of ears to be barren.  Some fields, on the other hand, had very poor pollination.  Corn rootworm beetle populations have also been very high in some fields and silk clipping occurred prior to pollination further reducing yield potential.  Continued dry weather will take its toll on the soybean crop as well.


A few web sites that you may want to follow are:


National Oceanic and Atmospheric Administration (NOAA) National Weather Service (NWS) Drought Statement


NOAA NWS Drought Monitor


NOAA NWS 6 – 10 Day Weather Outlook


NOAA NWS 8 – 18 Day Weather Outlook





For those wanting to estimate corn yields, its just a matter of counting kernels:

Pull several ears of corn at random and count the number of rows of kernels and the number of kernels per row.  Ignore kernels less than half size at the tip of the ear.  Also measure off 1/1000 acre along one row in several places in the field and count the number of ears:

1/1000 acre =        17 ft 5" in 30" rows

14 ft 6" in 36"

13 ft 9" in 38" rows
(For 20" rows, count 2 rows 13' 1" long)


Number of kernels per 1/1000 acre = kernels per row X rows per ear X ears per 1/1000 acre.

Divide this number by about 90 to get bu/A (since there are about 90,000 kernels per bushel).  If you think kernel size and weight will be smaller than normal, divide by a larger number (100+).



Two Spotted Spider Mites – They’re Back


Many fields that have been treated with chlorpyrifos (Lorsban 4E, Eraser, Nufos, etc.) once again have spider mite infestations.  An insecticide is recommended if spider mite damage is occurring in the field, mites are present, and hot, dry conditions are expected to continue.  If a second insecticidal treatment for spider mites is needed, use a different active ingredient than was used in the first application.  The Lorsban 4E label states that, if follow-up applications are needed, “make a follow-up application with a non-chlorpyrifos product that is effective against mites.”  Essentially that sugegsts a dimethoate product, such as Dimethoate 400, Dimate, etc.  Continue to monitor fields for two spotted spider mites until the field reaches maturity stage R7, which is when one normal pod on the main stem has reached its normal mature color, usually brown or tan.  For more information see the July 22, 2002 ICM Newsletter at and the July 18, 2005 article at


Soybean Aphids


Soybean aphid numbers have increased above the economic threshold in some fields.  Aphid numbers usually peak in mid-late July and then have a second peak in August.  Numbers have declined in some fields in the past week even when they are increasing in nearby fields.  Every field is different, so fields need to be monitored closely for at least a couple of more weeks.  Usually aphid numbers drop off rapidly sometime after mid-August.  Treatment is recommended if aphid numbers are increasing and surpass 250 aphids/plant.  The cooler temperatures will decrease moisture stress to the soybeans, but unfortunately may result in greater soybean aphid reproduction.  Under the right conditions, populations can double in 2-3 days, so 250/plant can increase to 1000/plant in less than a week.  For more information on soybean aphids, see and the July 11, 2005  ICM Newsletter at

Asian Soybean Rust


There have been more finds in the far southern U.S.  Almost all of the finds have been on sentinel plots, research plots, or on kudzu. For the latest see


Other Soybean Foliar Diseases


For some reason, downy mildew, a disease favored by cool, humid conditions, has been common this year in many soybean fields.  Frogeye leafspot is also showing up in some fields. Photos of common soybean diseases can be found at:


Soybean Cyst Nematode


With all of the attention on aphids and rust, don't forget the soybean pest in Iowa that still causes the most yield lost state-wide.  Damage from the pest is more evident in dry years. The July 25 ICM Newsletter at provides photos and scouting information to help deal with this pest.




Potato Leafhopper


Potato Leafhopper numbers continue to be high in many fields, so scouting of hay fields continues to be an important activity.  For information on managing potato leafhopper, see pages 107 - 110 of the June 21, 1999 Iowa State University Integrated Crop Management Newsletter or . A couple of sources for sweep nets are and


Late Summer (Fall) Seeding of Forages


Most likely, it will be too dry to attempt a late summer (fall) seeding of forage crops unless the weather becomes more moist and we can get the seeding done by August 20.  For more information, see Late Summer (Fall) Seeding of Forages.




Profitable Pastures – August 12, 2005, Lancaster Research Station, Lancaster, WI.


Northwestern Illinois Agricultural Research and Demonstration Center Field Day – 8:00 a.m., August 17, 2005, Monmouth, IL.


Andrew Jackson Demonstration Farm Field Day – 4:00 p.m., August 17, 2005, Andrew, IA.


Muscatine Island Research and Demonstration Farm (Horticulture) Field Day – 3:00 p.m., September 13, 2005, Fruitland, IA.


Southeast Research and Demonstration Farm (Agronomy) Field Day – 1:30 p.m., September 14, 2005, Crawfordsville, IA.


If you have any questions, please feel free to contact the Iowa State University Extension Office.
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Last Update: August 8, 2005
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