June 19, 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. 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 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.
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.
Asian Soybean Rust
On June 14th, a commercial
soybean field in
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
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:
FOR YOUR CALENDAR
Help Celebrate ISU’s 150th Birthday With Jack Payne at the
SE Iowa Research & Demonstration Farm Spring Field Day - Crawfordsville
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
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
Hybrid Results & Rating Corn Roots
Jon Tollefson, ISU Extension Entomologist
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:
Jim Fawcett, ISU Extension Crop Specialist
Ø Soil Bulk Density and Water Infiltration Rates with Different Tillage Systems
Mahdi Al-Kaisi, ISU Extension Agronomist – Soils
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
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
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
If you have any questions, please feel free to contact the Iowa State University Extension Office.
Nondiscrimination Statement and Information Disclosures