Iowa State University Extension and Outreach

East-Central and Southeast Iowa Crop Information

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July 22, 2005

July 22, 2005

 

SOYBEANS

Two Spotted Spidermites

 

Spider Mite problems are increasing in the area with the hot, dry conditions, with many fields being sprayed, especially east of the Cedar Rapids-Iowa City area. Since many are finding some soybean aphids as well, Lorsban has been the main product of choice. Hopefully the humidity that we have had will help to reduce the problems with the pest. For details on scouting for and managing this pest go to http://www.extension.iastate.edu/Pages/eccrops/spidermite.html or pages 148 - 149 of the July 22, 2002 Integrated Crop Management Newsletter.  Also see the recent article by Matt O'Neal on spider mites and aphids at http://www.extension.iastate.edu/news/2005/jul/071501.htm.

 

Soybean Aphids

 

Soybean aphids can be found in most fields in the area now, but in most cases the numbers are staying well below the economic threshold of 250 per plant. This may be due to the heat, since aphids reproduce most rapidly under cool conditions. We need to continue watching the fields, since numbers can increase rapidly. For more information on soybean aphids see http://www.ent.iastate.edu/soybeanaphid/ and the latest ICM Newsletter at http://www.ipm.iastate.edu/ipm/icm/2005/7-11/aphids.html.

Asian Soybean Rust

 

There are now 4 states where Asian Soybean rust has been confirmed this year (Florida, Georgia, Alabama, and Mississippi), but still only one commercial soybean field where rust has been confirmed in the country (in southern Alabama). The level of infection was very low in this field, so it was likely not a major source of spores. Wind patterns would have deposited any spores to the east of Iowa, and there is such a low amount of spores available that it is looking doubtful that we will see rust at all in Iowa this year. To see the latest visit http://sbrusa.net/.

ALFALFA

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 http://www.extension.iastate.edu/Pages/eccrops/potatoleafhopper.html. A couple of sources for sweep nets are  http://www.gemplers.com/a/shop/product.asp?T1=R13101&src=21SM001 and http://www.forestry-suppliers.com/product_pages/view_catalog_page.asp?id=5280.

 

CORN

Extended Diapause - Rootworm Problems in First Year Corn

 

A number of producers in Benton County are seeing corn lodging on soybean ground this year. Emergence traps that Pioneer has put out in the area has confirmed that northern corn rootworm beetles are emerging from the soil in some of these fields. Extended diapause, where the eggs take 2 years to hatch out, has occurred in NC and NW Iowa for many years, and has also been known to exist in pockets of EC Iowa. Any areas where the corn-soybean rotation has been the only rotation for many years is more likely to see this problem. Areas where there is more continuous corn is not as likely to have a problem. If you see corn lodging and many northern beetles (green in color) in corn on soybean ground, do some digging to confirm whether root feeding is occurring. Fields need to be identified to make decisions in the future how to best manage the problem.

 

 

DROUGHT

 

Although the severe drought conditions in general are to the east of the area I cover, the hot and dry weather is taking its toll on crops in the area. Iowa State University has created a Drought Information page on the World Wide Web at http://www.extension.iastate.edu/ag/droughtinfo.html.


Virgil Schmitt, who covers the area in extreme eastern Iowa, sent this information:

CORN

Situation

 

The days immediately leading up to tasselling through the first few days after pollination are critical to the corn plant.  This is the time when the plant is making the final determination of how many kernels it "thinks" it can carry to maturity.  The more stressed it is during that time, the shorter will be the ear it will try to keep.  Some fields have been showing much more stress than others, depending on location, soils, history, management, genetics, insect injury, etc.  The fields showing little stress still have excellent yield potential while the most severely stressed fields will be most valuable as silage.

 

Green Chop and Silage

 

Some corn fields are now being harvested as green chop or silage.  Be sure to check the WWW link above for details; http://corn.agronomy.wisc.edu/WCM/2003/W138.htm is especially noteworthy.  A few key points to remember when green chopping or making silage are:

1.  Be sure silage is at the correct moisture content for the storage method you have.  The visual queues you usually use may not be accurate with drought-damaged corn.

2.  Nitrates are seldom a problem.  If they are, it is when the drought-damaged corn silage is harvested within a few days after a significant rainfall.  The plant may take in a "big gulp" through the root system and not have the ability to move it into the kernel.

A.  If nitrate accumulation does occur, it will be in the bottom 12 - 18 inches, so cutting high will help.

B.  Many forage testing laboratories can test for nitrate in forage.

C.  After 2 - 3 weeks of fermentation in the ensiling process, the nitrate level dissipates greatly.  If you are still concerned, have the fermented product tested for nitrate.

D.  Cattle and sheep can tolerate 0.5% nitrate on a dry matter basis.

E.  Cattle and sheep can tolerate higher levels if feeding occurs over a period of several hours.

F.  Nitrate tolerance is increased if grain is fed.

G.  Gradually introduce cattle to suspect forages over a period of several days.

 

If you have any questions, please feel free to contact the Iowa State University Extension Office.
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Last Update: July 22, 2005
Contact: Jim Fawcett fawcett@iastate.edu


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