June 30, 2006
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 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. 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.
Soybean Aphids & Potato Leafhoppers
can be found in most soybean fields in the area, but fortunately leafhoppers
seldom cause economic problems in soybeans because of the hairs on soybean
leaves. The small leafhopper nymphs look similar to aphids, but I have not
found aphids in any soybean fields in EC or
So far there has only
been one case of rust being found on soybeans in the
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.
FOR YOUR CALENDAR
Walk July 6 - - 6:00 p.m. Steve Streets Farm East of Onslow (
Controlled Drainage and Tile Installation Field Day Wednesday, July 12
(Rain Date July 13)
9:00 a.m. to 4:00 p.m.
· Trenching and Plowing Equipment in Operation in the Field
· Shallow, narrow spacing of tile vs. wider, deeper spacing
· Controlled drainage experiment
· Constructed wetland to reduce nitrates in tile water
· Commercial & Educational Exhibits
11:00 a.m. 2:30 p.m. Special Session for CCAs with presentations by Dr. Matt Helmers and Dr. Jim Baker. Earn 3 hours of credit in soil and water ($40 fee). Send Jim Fawcett an e-mail note by July 10 if you plan to attend the CCA session or want more information.
Muscatine Island Research & Demonstration Farm Spring Field Day July 17, 2006 5:00 p.m.
Details will be forthcoming. This will have a commercial horticulture orientation.
If you have any questions, please feel free to contact the Iowa State University Extension Office.
Nondiscrimination Statement and Information Disclosures