June 18, 2007

 

CORN

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 0.75 – 1.0 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. This year, often there is evidence the soil was tilled and/or planted when the soil was just a little too wet.  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.

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. 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.

 

Striped Corn Leaves

Many corn fields have plants that are also showing striping on the upper leaves.  Most commonly, the symptoms are most consistent with Sulfur deficiency; see page 3 of IPM – 42 “Nutrient Deficiencies and Application Injuries in Field Crops” http://www.extension.iastate.edu/Publications/IPM42.pdf.

Our soils generally have quite sufficient amounts of sulfur available, so this phenomenon is generally an indicator of lack of root function, as has been discussed earlier.  As root function improves, new growth should not exhibit the striping.  However, on extremely sandy soils, soils that are severely eroded, and soils that have been adulterated while installing terraces or other structures,  sometimes a true sulfur deficiency does exist if the area has not had manure applied recently.  Soil tests for sulfur are quite unreliable.  Adding a sulfur compound to some of the area while leaving another area untreated and then making visual observations can help establish or eliminate this as a possibility.  Elemental sulfur is not quickly available, so use a sulfate compound instead.

 

Anhydrous 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.

 

Flag Leaf “Tied Up” & White Flag Leaves

Some corn fields have occasional plants where the flag leaf is “tied up”  within itself.  When the leaf finally breaks free, often it will be white or nearly white, causing people to be concerned about the possibility glyphosate drift.  The leaf tie up sometimes occurs during periods of very rapid growth.  When the leaf breaks free, it will be white because it has not been exposed to light and is not carrying on photosynthesis.  With the exposure to light, it will turn green within a few days and will be normal.  After the leaf breaks free, it will also usually have crinkling along the margins as a result of being tied up.  No long-term detrimental effects have ever been shown from this phenomenon.

 

HAY

Potato Leafhoppers

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.

 

Lepto Leafspot

Lepto Leafspot is showing up in many alfalfa fields.  In general, there is nothing that can be done except to harvest early to salvage as much leaf material as possible.  However, given the stress that hay fields that were frozen off in April and where the first cutting was made timely; the early cutting may be an additional stress that may shorten stand life expectancy.  For more information on Lepto Leafspot, see the following sites at The Ohio State University:

http://www.oardc.ohio-state.edu/ohiofieldcropdisease/alfalfa/lepto.htm

http://agcrops.osu.edu/cropdoc/b827_128.html

Clover Root Curculio

Some stands that are not recovering well after first cutting are also suffering from a somewhat rare insect infestation called clover root curculio.  The larval stage feeds on alfalfa roots and, if severe, can reduce stand longevity and vigor.  For more information, see the University of Kentucky site at http://www.ca.uky.edu/entomology/entfacts/ef119.asp.

 

FOR YOUR CALENDAR

SE Iowa Research & Demonstration Farm Spring Field Day, Crawfordsville - June 21, 2007 1:00 p.m.

11:00 a.m. Registration Begins

11:30 a.m. Lunch with and Comments from Vice-president  (Free lunch, meal reservations by June 19 required; call 319-337-2145 or e-mail fawcett@iastate.edu)

1:00 p.m.  Spring Field Day

 

¨     Crop Season Review & Marketing During Volatile Times– Kevin Van Dee, Farm Superintendent & Jim Jensen, ISU Farm Management Specialist

¨     Fungicides on Corn & Asian Soybean Rust Outlook
Daren Mueller, ISU Extension Plant Pathologist

¨     Moving CRP to Crops – Carbon Sequestration Impacts
Mahdi Al-Kaisi, ISU Extension Agronomist - Soil Management

¨     Rotation Resistant Corn Rootworms & Rating Corn Roots
Patti Prasifka, ISU Extension Entomologist

3:30 p.m.  Head Home

 

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:

8:30 a.m.  Registration - $50 Fee ($70 after June 19) – Includes Lunch

         

9:00 a.m. – noon Special Session for Certified Crop Advisors

(1.5 hours soil & water management, 1 hour pest management, 0.5 hours crop production)

 

¨     Alternative Crop Research in Iowa     

    Jim Fawcett, ISU Extension Crop Specialist

¨     Soil Bulk Density and Water Infiltration Rates with Different Tillage Systems

    Mahdi Al-Kaisi, ISU Extension Agronomist – Soils

¨     Fungicides – Review of Products & Research Results in Corn & Soybeans

    Daren Mueller, ISU Extension Plant Pathologist

 

If you plan to attend the CCA session, please send Jim Fawcett an e-mail note by June 19 (you can pay at the door). The fee is $70 for those not registered by June 19.

 

 

 

Muscatine Island Research & Demonstration Farm Spring Field Day – August 14, 2007 5:00 p.m.

Details will be forthcoming.  This will have a commercial horticulture orientation.

 

 

Northwestern Illinois Agricultural Research and Demonstration Center – August 21, 2007, 8:00 a.m., Monmouth, IL

Details will be forthcoming.