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June 19, 2007

June 19, 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. I often find that it is harder to dig in areas where the corn looks the best.

These symptoms are more likely to show up on soils that are low or marginal in K, so soil samples should be taken if the soil hasn't been tested recently. 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 Cropshttp://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.

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.  It is often seen when there is a big change in temperatures, especially when the weather changes from cool to very warm. 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.

 

SOYBEAN

Asian Soybean Rust

On June 14th, a commercial soybean field in Texas was confirmed to have soybean rust. This county had rust identified earlier in the year.  Moisture conditions vary with most areas remaining dry, although some additional rain has now occurred in the southeast and in parts of the high plains. The reports of rust occurrences to date are similar to last year with some exceptions of earlier reports of rust in Louisiana and in Texas on a commercial soybean field.  Still not much development of rust in the southeast U.S., but it continues to slowly spread.  Weather conditions are favorable for continued development of the disease. Current forecasts suggest that more typical rain patterns will continue in Florida which will favor soybean rust development and spread. For a map of where soybean rust has been found so far see http://www.sbrusa.net/.

 

Soybean Aphids

Since soybean aphids have tended to be worse in the odd numbered years, we need to be ready for this pest in 2007. I have not seen any aphids yet in fields that I have scouted, although they have shown up in low numbers in NE and central Iowa. Relatively high numbers have already been found in soybean fields in Ontario. For more information see the last ICM Newsletter at http://www.ipm.iastate.edu/ipm/icm/2007/6-11/aphids.html.

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

FOR YOUR CALENDAR

 

Help Celebrate ISU’s 150th Birthday With Jack Payne at the

SE Iowa Research & Demonstration Farm Spring Field Day - Crawfordsville

June 21

 

Doors open at 11:00 with a free health screening and displays on alternative energy, the bioeconomy, and trading carbon credits. A free lunch, courtesy of Farm Credit Services, is available at 11:30. Jack Payne, ISU Extension Vice President, will be speaking at 12:15. The farm tour begins at 1:00, where the stops include:

 

¨     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

¨     Bt-Rootworm Hybrid Results & Rating Corn Roots
Jon Tollefson, ISU Extension Entomologist

 

CCA Credit Opportunity – June 21 - Crawfordsville

 

Earn 5 hours of CCA credits, including 2 hours in soil and water, by attending a special CCA session beginning at 9:00 a.m. followed by the afternoon field day. The morning session will include:

 

Ø     Alternative Crop Research in Iowa   

Jim Fawcett, ISU Extension Crop Specialist

 

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

Mahdi Al-Kaisi, ISU Extension AgronomistSoils

 

Ø     Fungicides – Review of Products & Research Results in Corn & Soybeans - Daren Mueller, ISU Extension Plant Pathologist

 

There is a $50 registration fee ($70 after June 19). Give the Johnson County Extension Office a call or send me an e-mail note if you plan to attend. You can pay at the door.

 

NE Iowa Research & Demonstration Farm Field Day Nashua – June 28, 1:30-4:30

 

Tour topics include weed management (Bob Hartzler, ISU Extension Weed Scientist), corn rootworm (Marlin Rice, ISU Extension Entomologist), soybean insects (Matt O’Neal, ISU Entomology), and fungicides for corn and soybeans (Allison Robertson, ISU Extension Plant Pathologist).  Dutch-treat refreshments and an evening meal will be provided by the Riverton Lucky Clovers 4-H Club from 4:30 to 6:30 pm followed by the Horticulture Tour listed next.  Directions:  From the Hwy 218 & B60 intersection (Hwy 218 exit to Nashua), take B60 one mile west, then one mile south, and then one-quarter mile east to the farm. CCA Credits available.

 

 

Soybean Aphid and Bean Leaf Beetle Management Tour – August 8

 

Management techniques for the soybean aphid and bean leaf beetle will be highlighted at a tour on the Iowa Learning farm site on the Rob Stout farm south of West Chester on Wednesday, Aug. 8. Since first being discovered in the Midwest in 2000, soybean aphids have tended to be more of a concern in odd numbered years, so this may be more of a pest this year than last. No-till soybean plots that were planted with and without the seed treatment “Cruiser” are the focus of research conducted on this Iowa Learning Farm site. Seed applied insecticides can provide good early season bean leaf beetle control and also provide some control of soybean aphids, especially when planting is delayed as it was this spring. Also discussed at the tour will be value added crop opportunities, including “low lin” soybeans. A rain simulator will also be demonstrated at the site. A free meal, courtesy of QUALISOY (http://www.qualisoy.com/) will be available at 6:30 p.m. followed by the tour. The Iowa Learning Farm project is a unique partnership of agencies, farm and conservation groups, the general public and Iowa State University. Iowa Learning Farm project staff work to increase the adoption of residue management and conservation practices that are expected to improve water quality.

 

If you have any questions, please feel free to contact the Iowa State University Extension Office.

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Last Update: June 19, 2007
Contact: Jim Fawcett fawcett@iastate.edu


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