August 21, 2008
It appears that Soybean Aphid populations are continuing to increase in many fields. The later planted fields and fields where a preventive insecticide (killing the beneficial insects) was included in the last herbicide application appear to be the fields most commonly over the threshold for Soybean Aphid. Soybean aphids tend to not be as much of a problem in even-numbered years, but there are still some fields that need to be sprayed in those years, and, so far, it looks like 2008 will continue the pattern. The economic threshold is 250 aphids per plant with 80% of the plants being infested and with populations increasing. Once the soybeans reach growth stage R 5.5, an insecticide application is not needed. If there is a seed 1/8 inch in diameter in a pod at one of the top two nodes with a fully expanded trifoliolate leaf on the main stem of the plant, the plant is about right at R 5.5. Soybean aphid populations are declining in some fields, and if populations are declining or if the soybean aphids are preparing to leave the field, an insecticide application is not needed. So, take note of the presence of winged aphids and alatoid nymphs (with wing pads), high predator activity, and/or diseased aphids as these are all signs that the population is in decline or will leave the field shortly. Scout these same fields again within a few days to note if populations are increasing or decreasing.
An alternative for conventional scouting is to use the speed scouting method developed at the University of Minnesota. You only have to be able to count to 40 to use this method, but need to take a spreadsheet to the field to take notes and make a decision. You will most likely hit threshold with speed scouting before you actually hit the threshold using the conventional method. The data suggests that if you hit the threshold using the speed scouting method, there is an 82 per cent chance you will soon go over the threshold using the conventional scouting method. The following site describes the method and provides a link to download the spreadsheet. http://www.soybeans.umn.edu/crop/insects/aphid/aphid_sampling.htm.
Scouting techniques and management information can be found in SP 247, Soybean Aphids in Iowa 2007, which can downloaded from http://www.extension.iastate.edu/Pages/eccrops/transfer/07SBA.pdf.
I have been receiving many inquiries about when to expect feeding from Japanese Beetles to cease. There is a single generation in the Midwest, with beetles living for 30 45 days. Beetle feeding tends to occur from late June to early September, with the heaviest defoliation in July and August. With the generally cooler-than-normal weather, I would expect the beetles to live closer to 45 days than to 30 days. The population of beetles in many soybean fields exploded about July 12 14, so adding 45 days to that would suggest feeding will continue for most of the rest of August.
In soybean, the economic threshold for the beetles is the general leaf defoliation threshold used for other pests. During the reproductive stages of soybeans, the threshold for considering an insecticide treatment is if greater than 20% of the leaf area is gone due to feeding. However, the high price of soybean may lower the threshold slightly. But remember that most people tend to overestimate defoliation. If it looks like 20% defoliation, most likely its only 10%. The pictures in the following article can help in estimating percent defoliation: http://www.ipm.iastate.edu/ipm/icm/2002/7-29-2002/soydefoliation.html.
For more information and insecticides labeled for Japanese beetles see the July 28, 2003 ICM Newsletter at http://www.ipm.iastate.edu/ipm/icm/2003/7-28-2003/japanesebeetle.html.
Soybean Sudden Death Syndrome
Like 2007, Soybean Sudden Death Syndrome (SDS) is appearing in all of the counties I cover. However, thus far in 2008, it appears to be less severe than in 2007. Brown Stem Rot (BSR) can cause leaf symptoms identical to SDS. See pages 70 72 of the March 26, 2007 Integrated Crop Management Newsletter or http://www.ipm.iastate.edu/ipm/icm/2007/3-26/bsr_vs_sds.html for identification and management of SDS and BSR.
If the field has not been tested for Soybean Cyst Nematode (SCN), the presence of SDS in the field should prompt a soil test for SCN as SCN is usually present if SDS is present. The sample submission form and instructions for taking the sample are in PD-32 Plant Nemnatode Sample Submission Form which is available at Iowa State University Extension offices or can be downloaded from http://www.extension.iastate.edu/Publications/PD32.pdf.
FOR YOUR CALENDAR
Farm Progress Show
Tuesday, August 26 Thursday, August 28, 2008
Stop at the Iowa State University Building
See http://www.extension.iastate.edu/shows/fps08/ for more details.
Annual Field Day
Northwestern Illinois Research and Demonstration Center Monmouth, IL
8:00 a.m., Thursday, August 28, 2008
Program (Certified Crop Advisor Credits Available):
Sorting out the Good From the Bad; Identifying Beneficial Insects in Crops - Dr. Loretta Ortiz-Ribbing
Re-emergence of Pre-emergence Herbicides; Does it Make Sense? - Dawn Refsell
Managing for Higher Input of Costs Crop Production - Dr. Gary Schnitkey
Update on Old and New Pests: Corn Rootworm and Western Bean Cutworm - Dr. Kevin Steffey
Corn Planting Dates and Current Yield Prospects - Dr. Emerson Nafziger
See http://www.cropsci.uiuc.edu/research/rdc/monmouth/ for more details.
Fall Field Day
NE IA Research & Demonstration Farm Nashua
1:30 p.m., Thursday, September 4, 2008
Program (Certified Crop Advisor Credits Available):
· Grain Market Outlooks - Dr. Hart, ISU Extension Economist
· Considerations for fertilizing the 2009 crop - Dr. Sawyer, ISU Extension Soil Fertility Specialist
· Corn & Soybean Growth and Development/Stage of Maturity Relative to Planting Date - Ken Pecinovsky, Farm Superintendant
· Economics & Considerations of No-till & Tilled Systems - Andy Herringshaw, ISU Associate
· Foliar Fungicide Application Decisions & Plant Disease ID - Dr. Mueller, ISU Extension Plant Pathologist
See http://www.extension.iastate.edu/Pages/eccrops/meetnerf.html for more details.
Fall Field Day
SE IA Research & Demonstration Farm Crawfordsville
1:00 p.m., Wednesday, September 10, 2008
Tentative Program (check later for any updates) (Certified Crop Advisor Credits Available):
· Farm and Season Update - Kevin Van Dee, Farm Superintendent, and Mark Carlton, ISU Extension Field Agronomist
· Grain Handling, Drying, and Storing Shawn Shouse, ISU Extension Ag Engineer
· Farm Bill, Crop Financial Management in the Current Situation Jim Jensen, ISU Extension Farm Management Specialist
· Weed Management - Mike Owen, ISU Extension Weeds Specialist
See http://www.extension.iastate.edu/Pages/eccrops/meetserc.html for more details and any updates.
If you have any questions, please feel free to contact the Iowa State University Extension Office.
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