June 16, 2005
Stress-Induced K Deficiency in Corn
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.
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.
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.
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.
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 http://www.ipm.iastate.edu/ipm/icm/2005/06-13. You can
monitor where rust has been found at http://www.sbrusa.net.
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)
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 http://www.ipm.uiuc.edu/bulletin/article.php?issueNumber=12&issueYear=2005&articleNumber=9
FOR YOUR CALENDAR
Conservation Systems Field Day - June 22 10:00 a.m. Keokuk County
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.
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
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.