July 25, 2007
Iowa State University
Extension Information for Southeast Iowa
By Jim Fawcett, ISU Extension Field Agronomist
4265 Oak Crest Hill Rd. SE
Iowa City, IA 52246
Rotation Resistant Rootworms
Root feeding by rotation resistant rootworms played a role in causing
some of the lodged corn during last week’s storms. In most cases it is the
northern rootworm beetles that are being observed in these fields, indicating
that it was likely extended diapause populations from eggs laid two years ago
that is causing the problem. Emergence traps were placed in several eastern
Iowa corn fields this on soybean ground this month to try to get a better feel
of how widespread a problem we have with both the extended diapause northern
population and the western variant that is laying eggs in soybean fields.
Flattened corn has partly goosenecked back up, but most of the straightening
has been above the ear.
Soybean Aphid - Spraying Has Begun
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, with some
fields over the economic threshold in Jones County,
and some fields in Linn and Benton counties getting close to the economic
threshold. 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.
a little surprised to be seeing spider mites in quite a few fields, considering
that most of the area has received ample rainfall. 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 Lorsban, to avoid spider mite outbreaks.
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.
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
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 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
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
Soybean Aphid and Bean Leaf Beetle Management Tour - August 8
- 6:30 p.m.
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
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
Iowa Learning Farm project staff work to increase the adoption of residue
management and conservation practices that are expected to improve water
Pest Management Tour - August 27 - 6:00 p.m.
and soybean disease management and managing rotation resistant rootworms will
be featured at the Dean Folkman farm just east of Newhall. X.B. Yang will
discuss the results of a white mold fungicide trial on the farm and give a
soybean rust update. Early observations about fungicides sprayed on corn this
year will be discussed as well. Patti Prasifka, ISU Entomologist, will discuss
the results of the rotation resistant rootworm
monitoring that has been done in the area this year as well as management options
for the problem.