It 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
There 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 its 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 Elmores 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 State University web
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
It 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.
Another 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.
Some insecticide trial
results on aphids can be found at http://www.ipm.iastate.edu/ipm/icm/2006/1-23/insecticide.html.
See the latest Iowa
aphid information at http://www.ipm.iastate.edu/ipm/icm/2007/7-16/soybeanaphid.html.
More information is
available at http://www.extension.iastate.edu/Pages/eccrops/soybeanaphid3.html.
Jim 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
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
The 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 aphids.
FOR YOUR CALENDAR
Midwest Strip Till Conference July 31
9 a.m. to 3:00 p.m.
Organized by Research and Extension of Iowa State University, 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.
Bioeconomy and Continuous Corn
Field Day August 2
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 Scotts Outdoors, followed by the
program. An RSVP is requested
by July 30; please contact the Extension office at 800-992-0894
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. Mike 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
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 quality.
Muscatine Island Research and
Demonstration Farm Summer Field Day August 14
Drip irrigation will
be the emphasis of this field day. For more
information see http://www.extension.iastate.edu/Pages/eccrops/meetmusc.html.
Asian Soybean Rust
First Detector Training August 22
9:30 a.m. 3:30
Individuals 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.