June 18, 2007
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.
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 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:
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
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 email@example.com)
¨ 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
Corn Rootworms & Rating Corn Roots
Patti Prasifka, ISU Extension Entomologist
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)
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.
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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