Iowa State University Extension and Outreach

East-Central and Southeast Iowa Crop Information

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Soybeans

May 25, 2006

 

Soybeans

Bean Leaf Beetles

 

Bean leaf beetles are thick in many early planted soybean fields, especially in the southern part of the area. Scouting in central Iowa indicates that the overwintering populations are the second highest ever. Soybeans can take a beating this time of year from insect feeding and recover with little affect on the yield. Therefore it takes a lot of beetles of the overwintered generation to justify an insecticide treatment. The economic threshold is about 3 beetles per plant when the soybeans are in the VC stage and about 5 beetles per plant when the soybeans are in the V1 stage. However these thresholds ignore the potential for these beetles to transmit bean pod mottle virus. This is especially a concern for seed beans and food grade beans. In these fields an insecticide may be justified with considerably lower levels of beetles if an insecticide seed treatment was not used. An insecticide should not be sprayed unless beetles can still be found in the field. Last year the overwintered beetle numbers crashed about now. After they lay their eggs they will die on their own. Many fields should escape damage this year because of the delayed planting and emergence of soybeans. For more information on managing bean leaf beetles see the May 15, 2006 ICM Newsletter at: http://www.ipm.iastate.edu/ipm/icm/2006/5-15/blb.html

 

Asian Soybean Rust

 

Some sentinel plots in the south are starting to fill pods, and there are still no reports of rust on any soybeans planted this year anywhere in the U.S.

 

Corn

 

Know Your Grub Butts

 

Whenever grubs are found in a corn field, it has been important to differentiate between the true white grub, which has a three year life cycle, and the annual white grub. The true white grub can feed throughout the season and thus can cause stand and yield losses. There is no rescue treatment for the white grub. If there is enough stand loss to justify re-planting, a planter box insecticide treatment or seed treatment should be used. The annual white grub can cause some injury early in the season, but pupates in the late spring, so seldom if ever causes stand loss. The true white grub can be identified by looking at the raster (hair) pattern on tail end of the grub. True white grubs have two rows of parallel hairs, whereas the hairs on the annual white grub are random. See the May 15, 2006 ICM Newsletter for a picture of the true white grub raster pattern:

http://www.ipm.iastate.edu/ipm/icm/2006/5-15/insects.html

 

Now we have a third type of grub that is being found in some fields in eastern Iowa – the Japanese Beetle grub. This grub is being found in some fields in the Cedar Rapids area, where high populations of Japanese beetles occurred last year in soybeans. These grubs are also annual grubs, but they may do more feeding damage than what we have seen with other annual grubs. The raster pattern of the Japanese Beetle grub is in a “V-shape.” See this Virginia Tech publication for a picture of the Japanese Beetle grub and some information on damage that it can do to corn:

http://www.ext.vt.edu/pubs/entomology/444-106/444-106.pdf

 

Black Cutworms

 

Scouting should continue for black cutworms. There have been a few fields in the area that have reached the economic threshold (2-3% cutting with less than ¾-inch larva or 5% cutting with 1” larva), but problems have not been widespread. Continue scouting until there are 5 fully developed leaves (V5). See the May 1, 2006 ICM Newsletter for more details: http://www.ipm.iastate.edu/ipm/icm/2006/5-1/cutworms.html

 

Nitrogen Management

 

We are approaching the time to be pulling soil samples for the late spring soil nitrate test. Soil samples should be pulled to a one foot depth when the corn is 6-12” tall. It is best to use a systematic method rather than a random method to pull the samples. Pull the first sample in the corn row, the next 1/8 of the distance between rows, the next ¼ the distance between rows, etc. until you have worked your way across the rows. Do this at least twice for a total of 16 cores. This way you won’t by chance happen to be over or under representing areas that have higher bands of nitrogen (ie anhydrous bands, manure bands, starter fertilizer). Soil samples should be sent to a lab immediately after sampling. Results can help to fine-tune nitrogen management. For more details see the publication “Nitrogen Fertilizer Recommendations for Corn in Iowa” at http://www.extension.iastate.edu/Publications/PM1714.pdf for more details.

 

 

FOR YOUR CALENDAR

 

Pasture Walk & Double-Cropped Dry Field Pea Field Day

Evening of June 14 - Amana Farms

 

See the potentially new Iowa crop of dry field peas (on highway 6 about 1 mile west of highway 151 and 6 intersection) and learn about pasture management, controlling troublesome pasture weeds, and forage utilization at this 2 for 1 tour. See the ISU Extension Calendar at http://www.extension.iastate.edu/calendar/ in the near future for details.

 

SE Iowa Research & Demonstration Farm Field Day

Thursday, June 22 – Crawfordsville

 

9:00 a.m. Special Session for CCAs. Earn 5 hours of CCA credit (including 1.5 hours in soil & water) by attending this special morning session and the afternoon field day. $50 Fee (if pre-registered by June 20). Send me an e-mail note if you plan to attend.

 

The morning session includes:

·        “Goof Plots – Identifying Herbicide Injury Symptoms” (Jim Fawcett, ISU Extension Crop Specialist)

·        “Tillage Impacts on the Soil Environment, Soil Compaction, and Root Development” (Rick Cruse, ISU Professor of Agronomy – Soil Management)

·        “Know Your Spots – Identifying Foliar Soybean Diseases” (Alison Robertson, ISU Extension Plant Pathologist)

·        “Does the N Calculator Work in High Yield Environments?” (John Sawyer, ISU Extension Agronomist – Soil Fertility)

 

ISU Dean of Agriculture Wendy Wintersteen will be featured at noon with a presentation on “Future Direction of Ag Research”

 

1:00 p.m. – Field Day Tour. See http://www.extension.iastate.edu/Pages/eccrops/meetserc.html for details.

 

Controlled Drainage and Tile Installation Field Day

Wednesday, July 12 (Rain Date July 13)

SE Iowa Research & Demonstration Farm - Crawfordsville

 

9:00 a.m. to 4:00 p.m.

See:

·        Trenching and Plowing Equipment in Operation in the Field

·        Shallow, narrow spacing of tile vs. wider, deeper spacing

·        Controlled drainage experiment

·        Constructed wetland to reduce nitrates in tile water

·        Commercial & Educational Exhibits

 

11:00 a.m. – 2:30 p.m. Special Session for CCAs with presentations by Dr. Matt Helmers and Dr. Jim Baker. Earn 3 hours of credit in soil and water ($40 fee). Contact me by July 10 if you plan to attend or want more information.

 

 

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

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Last Update: May 25, 2006
Contact: Jim Fawcett fawcett@iastate.edu


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