June 16, 2005
Potassium Deficiency Symptoms
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.
Lang reported finding soybean aphids in
beginning to look like soybean rust is not likely to be a major problem in
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 http://www.ipm.iastate.edu/ipm/icm/2002/7-22-2002/spidermites.html.
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 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.
FOR YOUR CALENDAR
"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
If you have any questions, please feel free to contact the Iowa State University Extension Office.
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