June 21, 2010
WET & WEEDY
We have now had three wet springs in a row. Hopefully summer will bring some drier conditions (but not too dry). The persistent wet weather has kept field work to a minimum which means fields are getting pretty weedy. Be sure to check labels regarding maximum corn height when applying herbicides. Drop nozzles will likely be needed in many fields to get good coverage and reduce the injury risk to corn. It is getting hard to see the soybean rows in many fields, which illustrates the value of using a soil applied herbicide in a Roundup Ready system. See Bob Hartzler’s article if you’d like to know how much yield we are losing with the weedy fields at http://www.extension.iastate.edu/CropNews/2010/0615hartzler.htm.
Stress Induced K Deficiency
are again seeing corn fields with areas in the fields that are stunted with the
lower leaves yellowing and browning along the margins. This is a symptom of K
deficiency, but is often due to poor root function rather than a shortage of K
in the soil. The endrows are often better than the
rest of the field, probably due to the different soil structure where the
traffic and/or tillage pattern has been different. Usually the fields look fine
until the corn gets to be about knee high, then corn
in areas of the field stop growing and the lower leaves turn yellow. Good corn
can be right next to extremely stunted corn with no apparent reason for it. The
corn in these areas remain stunted and the lower leaves remain yellow, but they
usually yield better than expected.
Anything that restricts root growth during the initiation of the nodal root system, such as side-wall compaction, can lead to the problem. The nodal roots emerge within an inch of the soil surface. If there is something in the surface inch or so that the roots don't "like" they don't function properly. There can be large differences among hybrids in showing this phenomenon. Shallow planting and/or soil settling or eroding after planting aggravates the problem. The problem is more likely to show up in soils that are low or marginal in K levels, so if the soil hasn't been tested recently, soil samples should be taken. In many fields it is difficult to come up with an explanation for why the problem is appearing. It is most common in no-till fields, but shows up in tilled fields as well. In tilled fields, it can show up where the soil is fairly "fluffy.” Many commented on how mellow the soil was earlier this spring. Since the endrows usually look better, it could be that a little surface compaction actually helps to alleviate the problem. There is nothing that can be done when the problem appears.
Sulfur deficiency problems are starting to be more common in both corn and alfalfa, partly because we no longer receive much sulfur in the rainfall since the power plants have added scrubbers to their smoke stacks. I’ve seen a couple of corn fields this spring that looked like they were suffering from sulfur deficiency. One symptom is interveinal chlorosis (striping) on the upper, younger leaves. If these symptoms are worse on the low organic matter, sandy soils, sulfur deficiency is a possibility. For some pictures of sulfur deficiency symptoms in corn and alfalfa, see John Sawyer’s photo gallery at http://www.agronext.iastate.edu/soilfertility/photos/photossecmicr.html. On sandy soils with a history of sulfur deficiency problems, 25 lb/A of S is recommended. Manure is also a good source of sulfur. For information on dealing with sulfur deficiency in corn see http://www.agronext.iastate.edu/soilfertility/info/Sulfur_ICM_Proc_2009.pdf.
FOR YOUR CALENDAR
SPRING FIELD DAY & SPECIAL SESSION FOR CCAs
SE IA RESEARCH FARM – CRAWFORDSVILLE
Deadline to Register for Lunch or CCA Session is June 22
Certified Crop Advisors can obtain 5 hours of credit (including 3 hours in soil and water management) by attending a special session in the morning followed by the afternoon tour at the ISU SE Iowa Research & Demonstration Farm near Crawfordsville on June 24. There is a $50 fee ($70 after June 22) for CCAs attending for credit (includes lunch). There is no charge for the afternoon field day except an $8 fee for those wanting lunch at noon. Fees (check or cash) can be paid at the door, but if you plan to attend the morning session or want to reserve a lunch at noon, please send me (firstname.lastname@example.org) a note by June 22.
Special Session for Certified Crop Advisors (8:30-noon)
Ø Goof Plots – Herbicide Injury Symptoms
Jim Fawcett, ISU Extension Field Agronomist
Ø How do we design subsurface drainage systems considering crop production and water quality?
Matt Helmers, ISU Extension Ag Engineer
Ø Environmental Impacts of Perennial Energy Crops
Emily Heaton, ISU Extension Agronomist
Noon – Lunch (Includes homemade ice cream)
Spring Field Day Tour (1:00-3:00)
Ø Crop Season Review & Soil Drainage Research Results - Kevin Van Dee, Farm Superintendent & Matt Helmers, ISU Extension Ag Engineer
Ø Cover Crops & Nitrogen Management – John Sawyer, ISU Extension Agronomist – Soil Fertility
Ø Research on Miscanthus & Other Crops for Cellulosic Ethanol – Emily Heaton, ISU Agronomist
Ø New Developments in Soybean Aphid Management – Erin Hodges, ISU Extension Entomologist
Muscatine Island Research Farm Field Day and 75th Anniversary, Fruitland
The Muscatine Island Research and Demonstration Farm was founded 75 years ago. A special field day will include many special events in addition to the traditional field day. If you have an interest in horticulture, be sure to attend. Information will appear soon at http://www.extension.iastate.edu/Pages/eccrops/meetmusc.html.
Northeast ISU Research Farm Field Day, Nashua
Field day speakers include: Ken Pecinovsky, Farm Superintendent, Robert Hartzler, ISU Extension Weed Scientist, Alison Robertson, ISU Extension Plant Pathologist, John Sawyer, ISU Extension Soil Fertility Specialist, Chad Ingels, ISU Extension Program Specialist, and Brian Lang, ISU Extension Agronomist. CCA Credits available for a fee.
If you have any questions, please feel free to contact the Iowa State University Extension Office.
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