July 25, 2007
has been about a week since storms injured some fields. Now we can begin to get a better feeling for
the extent of the damage done to yields.
In corn, most of the stalk straightening is occur near or above the ear
leaf, making harvest a challenge. Some research at the University of Wisconsin
indicated about a 15-30% yield loss when corn is flattened at the pollination
were also smaller areas where hail damage occurred. About one third of the corn
yield is lost with a 50% loss of leaf area at silking.
Assessing Hail Damage to Corn (NCH-1) http://www.extension.iastate.edu/Publications/NCH1.pdf
can help in estimating potential yield losses. Of course it’s important to get
the insurance person out to look at corn and soybean fields if you have hail
insurance. Lodging and hail also increase the incidence of plant
diseases, including stalk rots. See Roger Elmore’s 2005 ICM
article for more discussion on corn lodging at http://www.ipm.iastate.edu/ipm/icm/2005/8-1/rootlodge.html.
Nitrogen losses from the heavy rains are showing up in
fields now. Symptoms begin with the
lower leaves and move up the plant and consist of leaf yellowing beginning art
the leaf tip and moving down the center mid-rib, forming a V pattern. See the South Dakota
web site http://plantsci.sdstate.edu/soiltest/Nutrient_Deficiency_Pages/CornD.html
and the University
of Minnesota web site http://www.extension.umn.edu/cropenews/2002/nutrientdeficiencyflowchart.pdf
for more pictures. Some yield increases
have been seen with additional nitrogen applications up until VT (tassel
emergence), but the odds of a response go down fairly rapidly after that time.
Soybean Aphid - Spraying Has Begun
Brian Lang reports that many
fields have been sprayed in Winneshiek, Clayton, and Allamakee counties in NE Iowa, with some fields having over 1000 aphids per
plant. Spraying has also begun in the northern part of east central Iowa. In general, it appears that numbers are still
below the economic threshold but are increasing. Aphid numbers can vary substantially from
field to field, so it is important to scout now and not spray unless the
threshold of 250 per plant (& at least 80% of the plants infested) is
reached. If fields are sprayed too soon, it is more likely that they will have
to be re-sprayed. It is also likely that many fields will not reach the
economic threshold. If you are going to
spray for soybean aphid, be sure to see item on spider mites following this
is best to count all aphids on a few plants to get a feel for what 100 and 250
look like and then estimate from that point on.
method of scouting developed at the University
of Minnesota that can
help to speed up the process can be found at http://www.soybeans.umn.edu/crop/insects/aphid/aphid_sampling.htm.
insecticide trial results on aphids can be found at http://www.ipm.iastate.edu/ipm/icm/2006/1-23/insecticide.html.
the latest Iowa
aphid information at http://www.ipm.iastate.edu/ipm/icm/2007/7-16/soybeanaphid.html.
information is available at http://www.extension.iastate.edu/Pages/eccrops/soybeanaphid3.html.
Fawcett and I are both a little surprised to be seeing two-spotted spider mites
in quite a few soybean fields, considering that most of the area has received
ample rainfall. I even ran into a field under center pivot irrigation with
substantial numbers of spider mites. The
two week stretch of hot, dry weather must have allowed populations to build up.
Although the level of infestation is low, if spider mites are found in a field
that is going to be sprayed for aphids, it would be best to use a product that
controls both pests, such as chlorpyrifos (Lorsban and the generics), to avoid spider mite
outbreaks. See http://www.extension.iastate.edu/Pages/eccrops/spidermite.html
for more information.
Sudden Death Syndrome
and Brown Stem Rot
Soybean Sudden Death Syndrome (SDS) is showing up in
some soybean fields and I am occasionally running into Brown Stem Rot
(BSR). See pages 70 –
72 of the March 26, 2007 Integrated Crop Management Newsletter or http://www.ipm.iastate.edu/ipm/icm/2007/3-26/bsr_vs_sds.html
for identification of SDS and BSR.
Asian Soybean Rust
threat has increased that we may eventually see some Asian soybean rust this
year in Iowa,
although the chances are still less than 40%, according to X.B. Yang.
Widespread problems with rust are now being found in northern Texas,
and X.B. reports it will likely be found in Oklahoma soon. It has also been found for
the first time this year in Arkansas.
Because of the increased risk for Iowa,
sentinel plots in the state will be monitored more frequently in August.
Hopefully if it does arrive in Iowa
it will be late enough in the season so the impact will be minimal. For the
latest on where rust (and aphids) is being found see http://www.sbrusa.net/. Click on the little
arrow next to soybean aphid in the upper right corner to change the map to
FOR YOUR CALENDAR
Midwest Strip Till Conference – July 31
9 a.m. to 3:00 p.m.
Organized by Research and Extension of Iowa
the University of Minnesota, the University
of Wisconsin, and Hawkeye Community College.
Manufacturers will demonstrate equipment for strip-tillage and associated
operations, including auto-guidance systems and fertilizer injectors.
Researchers, farmers, and industry representatives will present the latest
information on strip-tillage related topics, including equipment selection,
fertility management, and guidance technology. Participants will review
information booths all day, and lunch is available on site. This program
is free and open to the public. Five Certified Crop Advisor CEUs (4.5 SW &
0.5 NM) will be available for a nominal fee. Expo details are at: http://wrc.umn.edu/outreach/striptillageexpo/midwest/index.html.
Continuous Corn “Field Day” – August 2
The public is
invited to attend
a “field day” in the Muscatine County Extension Office, 1514 Isett Avenue, Muscatine, on Thursday, Aug. 2, from 6-8:30
p.m. A complimentary dinner will be served courtesy of
Scott’s Outdoors, followed by the program.
RSVP is requested by July 30; please contact the Extension office at 800-992-0894 or 563-263-5701.
Hot topics for discussion will be the bioeconomy and no-till continuous corn production. Other
agenda items include swine manure application costs and nutrient values.
Deahr and Doug Nolte, both Muscatine
County cooperators with
the Iowa Learning Farm, will be discussing their farming practices and Iowa State University Extension Water Quality Engineer Dr. Matt Helmers
will demonstrate the ILF conservation systems rainfall simulator.
The Iowa Learning Farm is a partnership
between the Iowa Department of Agriculture and Land Stewardship; Iowa State
University Extension; Leopold Center for Sustainable Agriculture; Iowa Natural
Resources Conservation Service, in cooperation with Soil and Water Conservation
Districts of Iowa, Iowa Department of Natural Resources and
Iowa Farm Bureau.
Soybean Aphid and Bean Leaf Beetle Management Tour – August 8
Management techniques for the soybean aphid
and bean leaf beetle will be highlighted at a tour on the Iowa Learning farm
site on the Rob Stout farm south of West Chester
on Wednesday, Aug. 8. Since first being discovered in the Midwest
in 2000, soybean aphids have tended to be more of a concern in odd numbered
years, so this may be more of a pest this year than last. No-till soybean plots
that were planted with and without the seed treatment “Cruiser” are the focus
of research conducted on this Iowa Learning Farm site. Seed applied
insecticides can provide good early season bean leaf beetle control and also
provide some control of soybean aphids, especially when planting is delayed as
it was this spring. Also discussed at the tour will be value added crop
opportunities, including “low lin” soybeans. A rain
simulator will also be demonstrated at the site. A free meal, courtesy of
QUALISOY (http://www.qualisoy.com/) will
be available at 6:30 p.m. followed by the tour. The Iowa Learning Farm project
is a unique partnership of agencies, farm and conservation groups, the general
public and Iowa State University.
Iowa Learning Farm project staff work to increase the adoption of residue
management and conservation practices that are expected to improve water
Muscatine Island Research and Demonstration Farm Summer Field Day –
irrigation will be the emphasis of this field day. For more information see http://www.extension.iastate.edu/Pages/eccrops/meetmusc.html.
Soybean Rust First Detector Training – August 22
a.m. – 3:30 p.m.
who have not gone through the Asian Soybean Rust First Detector training or
First Detectors who would like a refresher should plan to attend one of the
trainings during the week of August 20.
The closest training is the one in Muscatine
on August 22 at the Muscatine Island Research and Demonstration Farm at
Fruitland http://www.extension.iastate.edu/Pages/eccrops/meetmusc.html. Details will be forthcoming.