Iowa State University Extension and Outreach

East-Central and Southeast Iowa Crop Information


CROP UPDATE 6/16/2005

June 16, 2005

Stress-Induced K Deficiency in Corn

        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 endrows 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 knee 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 endrows 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. Antonio Mallarino will have an article in the next ICM Newsletter regarding the problem.

Insect Update

Soybean Aphids

        Brian Lang reported finding soybean aphids in NE Iowa on June 1. The bad news is this is the earliest he has found soybean aphids and the percent infested plants he is now finding is similar to what was found in 2003. The good news is the level of infestation (aphids per plant) is much lower than in 2003 and the number of beneficial insects he is finding is much higher. Perhaps mother nature is getting back in balance. Normal rainfall levels should help to keep the pest in check.


        Several growers have reported that millipedes have caused some stand loss in both corn and soybean fields this year by feeding on the seed prior to emergence. This is very unusual, since millipedes normally do not feed on live plant tissue. It is likely related to the very cool spring and slow emergence of the crops.

Disease Update

Soybean Rust

        Its beginning to look like soybean rust is not likely to be a major problem in Iowa this year. There have still been no reports outside of Florida and southern Georgia, despite extensive scouting. There has been another rust find on kudzu in a county in Florida that produces soybeans. Comments from X.B. Yang on soybean rust, including the potential impact of tropical storm Arlene can be found in the latest ICM Newsletter at You can monitor where rust has been found at

Weed Update

Herbicide Carryover

        There have been a few instances of problems with crop injury from herbicide carryover of several products this spring. The cool, dry August last year may have reduced the breakdown of some herbicides.

Equisetum (Scouring Rush, Field Horsetail, Snakegrass)

        This weed seems to be causing more concern recently. It is an ancient plant that has been around since the dinosaurs. Unfortunately it is very difficult to control. In the vegetative stage it looks like little Christmas trees, and in the reproductive stage it consists of hollow jointed tubes. Tillage can help to eventually thin it out. Other than soil sterilants, herbicides are not very effective. Glyphosate has no effect on it. A fact sheet on the weed and possible control methods can be found at .


Conservation Systems Field Day - June 22 10:00 a.m. Keokuk County

        Conservation Tillage systems will be highlighted at this field day on the John Kiekolf farm near Hedrick. The program will include Conservation system benefits for soil and crop yields, equipment considerations for succesful conservation systems, conservation systems and water quality, conservation security program overview, economics of conservation systems, and soybean rust/aphid update. To reach the site; from Hedrick go west 4.25 miles on Hwy 149.

SE Iowa Research & Demonstration Farm Spring Field Day - June 23 1:00 p.m.

        "Asian Soybean Rust Outlook", by Alison Robertson and X.B. Yang, will be the featured presentation at the annual spring field day tour at the Crawfordsville Research Farm. Also featured on the tour will be "Tile Drainage on SE Iowa Soils", by Greg Brenneman, ISU Extension Ag Engineer; "Vertical Tillage Results, Soil Conservation Progress and Rewards in Iowa, & Crop Season Review", by Bruce Trautman, NRCS Area Conservationist & Kevin Van Dee, ISU Farm Superintendent; and a choice between "Soybean Aphids - Will They Be Back?", by Matt O'Neal, ISU Entomologist, or "Is Grape Production For You?", by Patrick O'Malley, ISU Extension Horticulturist.

Brush up on Your Soybean Disease Identification Skills and Earn CCA Credits - Crawfordsville - June 23

        Other foliar soybean diseases will be showing up in June, regardless of whether soybean rust makes its way to Iowa. Can you tell the difference? Certified crop advisors can earn 5 CCA credits by attending a special CCA session in the morning of June 23 followed by the SE Iowa Research & Demonstration Farm Spring Field Day Tour in the afternoon. The morning session will focus on Foliar Soybean Disease Identification and will also feature a presentation on soil & water conservation. This would be a good review for soybean rust first detectors. The session starts at 9:30 a.m. If you are not a first detector and wish to become one you need to show up a half hour early (9:00 a.m.). By attending the morning session and the afternoon field day tour you can earn 3 hours in pest management and 2 hours in soil & water management. There is a $50 fee, which includes lunch. If you plan to attend, please send me an e-mail note by June 21 (you can pay at the door). The fee is $70 for those not registered by June 21.


If you have any questions, please feel free to contact the Iowa State University Extension Office.
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Last Update: June 16, 2005
Contact: Jim Fawcett

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