June 12, 2006
Potassium Deficiency Symptoms
We 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 end rows 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 calf 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 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. If the soil hasn't been tested recently, soil samples should be taken to make sure it is not a true K deficiency problem. Soils that are low or marginal in K are more likely to show the problem. In many fields it is difficult to come up with an explanation 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", especially under dry conditions. Since the end rows 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. An excellent discussion of this problem in both corn and soybean is on pages 123 – 124 of the June 20, 2005 Integrated Crop Management (ICM) Newsletter or at http://www.ipm.iastate.edu/ipm/icm/2005/6-20/potassium.html.
Nitrogen Deficiency Symptoms
We are also seeing many fields with nitrogen deficiency. When manure or commercial fertilizer was knifed in, often alternating streaks of dark green verses yellow-green corn can be observed. As the roots reach the nutrients, color should improve.
Anhrdrous Ammonia Injury
I am also observing more injury than usual from anhydrous ammonia burn. Injury browns the roots, and, if injury is severe, roots can die and turn black. In the case of the primary / seed / seminal root system, roots may die back to the seed. Pictures can be seen on page 5 in IPM – 42 “Nutrient Deficiencies and Application Injuries in Field Crops” or at http://www.extension.iastate.edu/Publications/IPM42.pdf.
Stalkborers are moving from grassy areas to adjacent
corn plants in areas north of approximately Highway 92 (
High numbers of potato leafhoppers can be
found in some hay fields. Be sure to also use a sweep net to monitor
potato leafhopper numbers and treat if numbers exceed the threshold. For
more 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.
Remember, waiting to see hopperburn is waiting too
long as substantial losses have already occurred by that time.
FOR YOUR CALENDAR
SE Iowa Research & Demonstration Farm Spring Field Day, Crawfordsville - June 22, 2006 1:00 p.m.
11:30 a.m. Registration Begins
12:00 noon Lunch with and Comments from Dean Wendy Wintersteen ($5 fee for lunch, meal reservations by June 20 required; call 319-337-2145 or e-mail email@example.com)
· Crop Season Review -- Kevin Van Dee, Farm Superintendent
· Early Planting Options Using Polymer Coatings -- Claude Butt, Landec Ag
· Asian Soybean Rust Outlook & Fungicide Trial Results -- Alison Robertson, ISU Extension Plant Pathologist
· Corn Population & Planting Date Trial Results -- Roger Elmore, ISU Extension Corn Specialist
· Diagnostic Tools for Nitrogen Management -- John Sawyer, ISU Extension Agronomist Soil Fertility
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)
If you plan to attend the CCA session, please send Jim Fawcett an e-mail note by June 20 (you can pay at the door). The fee is $70 for those not registered by June 20.
Controlled Drainage and Tile Installation Field Day – Wednesday, July 12 (Rain Date July 13), 2006
9:00 a.m. to 4:00 p.m.
· 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 Jim Fawcett by July 10 if you plan to attend the CCA session or want more information.
Muscatine Island Research & Demonstration Farm Spring Field Day – July 17, 2006 5:00 p.m.
Details will be forthcoming. This will have a commercial horticulture orientation.
Illinois Agricultural Research and
Details will be forthcoming.
If you have any questions, please feel free to contact the Iowa State University Extension Office.
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