Iowa State University Extension and Outreach

East-Central and Southeast Iowa Crop Information


June 16, 2005

June 16, 2005



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 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 end rows 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.


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.

Soybean Rust

It's 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


Two-spotted Spidermites

I ran into a field where two-spotted spidermites were damaging soybean.  Interestingly, it was on heavier soil where there had been some rainfall recently.  For information on scouting for and managing two-spotted spidermites in soybean, see pages 148 - 149 of the July 22, 2002 Integrated Crop Management Newsletter or


Potato Leafhoppers

High numbers of potato leafhoppers can be found in many 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  Remember, waiting to see hopperburn is waiting too long as substantial losses have already occurred by that time.


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 Southeast Research and Demonstration Farm, Crawfordsville. 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 - SE Iowa Research and Demonstration Farm - June 23

Other foliar soybean diseases will be showing up this summer, 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 Jim Fawcett 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
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