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East-Central and Southeast Iowa Crop Information

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July 12, 2010

 

CORN

 

Japanese Beetles

 

Japanese beetles can be easily found in some corn fields in Clinton, Jackson, Muscatine, and Scott Counties.  Generally, they do not cause economic injury to corn unless they are keeping silks clipped to within one-half inch of the end of the ear prior to pollination being complete; generally it takes three or more beetles per ear to accomplish this level of feeding.  Once pollination is complete, the silks can be eaten entirely away without causing yield loss.

 

For more information on Japanese beetles and their management, see http://www.extension.iastate.edu/CropNews/2009/0630hodgson.htm and http://www.extension.iastate.edu/CropNews/2009/0727hodgson.htm.

 

 

SOYBEAN

 

What’s eating my soybeans?

 

Bean leaf beetle numbers continue to be low, but Japanese beetles, green cloverworms, and/or larvae identified by Tom Hillyer, Hillyer AgriService,  as celery leaftiers are causing noticeable feeding in some fields.  For soybeans in or past beginning bloom, the threshold for treatment is 20% loss of total leaf area.  In general, soybean defoliation looks worse than it is.  The following graphic may help you in determining the level of defoliation.

 

Soybean defoliation

 

For more information on Japanese beetles and their management, see http://www.extension.iastate.edu/CropNews/2009/0630hodgson.htm and http://www.extension.iastate.edu/CropNews/2009/0727hodgson.htm.

 

For more information on green cloverworms and their management, see http://www.extension.iastate.edu/CropNews/2010/0712hodgson.htm.

 

Celery leaftiers are not known to be a problem in soybean, so information related to soybean is scarce.  The mature larva is slender and pale green with a narrow, darker green band along the back and with a broader, whitish band along each side, and it tapers toward each end. The underside of the caterpillar is yellowish and faintly mottled with brownish yellow. The full grown larva is two-thirds to three-fourths of an inch long.  The larvae usually damage the underside of the leaves by skelonizing them. The plants have a silvery appearance when heavily infested. Later, the damaged areas become pitted. A slight, silken web is spun in a leaf, or between two adjacent leaves and the leaf is folded or woven together to form a shelter area in which the larvae feed; thus, the name leaftier.  They seem to be concentrating in the lower part of the soybean canopy.

 

 

Soybean Aphids

 

Brian Lang, my counterpart to the north, reports, “Initial aphid migration from Buckthorn to soybeans in May-early June was at a low level.  The wet June kept aphids at low levels.  Summer migration of aphids usually begins around mid-July to spread to other fields.  With these low initial aphid populations, it is uncertain as to how rapid or how high a population of aphids can develop.  That’s why we continue to scout.  On July 11 at this trial I found my first winged aphids (only 4 so far) since the migration of aphids from Buckthorn.  So this marks the beginning of the summer migration.  However it is starting from very low initial populations, so no one can predict yet if aphids will be much of a problem.  … populations (are) still matching up with low populations from other “even” years.  The rapid increase in populations in 2008 appeared to come from a summer migration of winged aphids from Minnesota.  Without that, we would likely not have had much trouble from aphids in this region in 2008.”

 

 

FOR YOUR CALENDAR

 

 

Northeast Iowa Research and Demonstration Farm, Nashua

Demonstration Garden Field Day on August 7,, 2010 at 4:00 p.m.

Fall Field Day on August 26, 2010, 1:30 p.m.

 

Details are and will be posted at http://www.extension.iastate.edu/Pages/eccrops/meetnerf.html.

 

 

Muscatine Island Research and Demonstration Farm, Fruitland

Demonstration Garden Field Day on August 9,, 2010 at 6:30 p.m.

 

Details are posted at http://www.extension.iastate.edu/Pages/eccrops/meetmusc.html.

 

 

Southeast Iowa Research and Demonstration Farm, Crawfordsville

Fall Field Day on September 15, 2010

 

Tentatively there will be a manure application field day in the morning followed by a “more traditional” field day in the afternoon.  More details 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: July 13, 2010
Contact: Virgil Schmitt vschmitt@iastate.edu


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