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 firstname.lastname@example.org)
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.
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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