August 23, 2008
State University Extension Information for Southeast Iowa
By Jim Fawcett, ISU Extension Field Agronomist
4265 Oak Crest Hill Rd. SE
Iowa City, IA 52246
Soybean aphid numbers have declined in most fields now and most soybean fields are at or near R6 (full seed size) when treating for soybean aphids is less likely to pay, so hopefully we are done with aphids for one more year. Populations should be dropping soon in fields where the numbers are still high, as the winged aphids return to buckthorn plants to lay their eggs.
Bean Leaf Beetles
Bean leaf beetle numbers have been extremely low in fields that I have been in the last 2 weeks. The later planting of soybeans this year probably helped to keep beetle numbers low earlier in the season and itís possible that the recent wet weather may reduce the population of the 2nd generation beetles. Hopefully this is a pest we wonít have to deal with this summer, but fields should continue to be scouted.
Northern Corn Rootworm Beetles
The most numerous insect pest (other than
aphids) being found in most soybean fields again this summer is the northern
corn rootworm beetle (greenish beetle about the size of bean leaf beetles).
Fortunately the beetle seldom does enough leaf feeding in soybeans to cause
economic problems, although they will feed on soybean leaves. It is another
indication to me that we do have problems with this pest in rotated corn, since
itís likely that this is where many of the beetles are coming from. Managing
the problem on rotated corn will be discussed at the field day in
Sudden Death Syndrome
Soybean sudden death syndrome is more
widespread than Iíve ever seen it in the past. I can find it in most soybean
fields that Iíve been in, although in most cases it is in fairly small patches.
It occurs most in areas where there has been some soil compaction, such as in
end rows, or where the drainage is poor. The disease is caused by a soil borne
fungus and the infection of the plants actually occurred early in the growing
season. The disease is not actually spreading from plant to plant as it may
appear as the patches become larger. Early planting in cool wet soils and
flooding during the vegetative stages will increase the problems with this
disease. Although early planting was not common this year, the excess rain that
many areas of eastern
Asian Soybean Rust
X.B. Yang now predicts that there is a
greater than 50% chance that
Virgil Schmitt has reported seeing some corn fields that are exhibiting double
or multiple ears developing from one node. This is a phenomenon called
ďtwinningĒ that was observed from
It is quite easy (if not always accurate) to estimate corn yields, since itís
just a matter of counting kernels. Maybe the heat & humidity will drop one
of these days so corn yield estimates can be taken without dieing from heat
exhaustion. To estimate corn yields pull several ears of corn at random and
count the number of rows of kernels and the number of kernels per row. Ignore
kernels less than half size at the tip of the ear. Also measure off 1/1000 acre
along one row in several places in the field and count the number of ears:
1/1000 acre = 26 ft 2Ē in 20Ē rows (or measure 13 ft 1Ē and count ears in 2 rows)
17 ft 5" in
14 ft 6" in 36" rows
13 ft 9" in 38" rows
Number of kernels per 1/1000 acre = kernels per row X rows per ear X ears per 1/1000 acre.
Divide this number by about 90 to get bu/A (since there are about 90,000 kernels per bushel).
FOR YOUR CALENDAR
White Mold, Sudden Death, Rotation Resistant Rootworms & Fungicides on Corn
Corn and soybean disease management and managing
rotation resistant rootworms will be featured at the Dean Folkmann
farm just east of Newhall (just west of Linn Coop). 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. BASF and Linn Coop.
will be providing a free meal and 6:00 p.m. followed by the tour. If you plan
to attend, please call the
Fall Field Day
September 6 - 1:30 p.m.
Topics will include grain storage issues, grain marketing, low linolenic soybeans and other alternative crop opportunities, and managing extended diapause northern corn rootworms.
If you have any questions, please feel free to contact the Iowa State University Extension Office.
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