August 13, 2007
Soybean Aphid Update - Many Fields Over Economic Threshold
Many fields are over the economic threshold of 250 aphids per plant (& 80% of plants infested) and spraying has been going strong. Some have seen aphid numbers decline recently in fields that haven't reached the threshold, so fields need to be scouted to determine whether an insecticide treatment is justified. The hot weather may be doing some good. Some studies have shown that soybean aphid's rate of reproduction slows with temperatures above 86F and stops at 95F. Heavy rains may reduce aphid numbers somewhat, but it is not likely that rains will solve the problem.
Many are seeing the small white aphids again this August. These are soybean aphids and are also causing damage, so should not be ignored. Don't confuse the shed white skins with the living aphids. And look closely to see if the majority of aphids are winged or have broad shoulders, which means they have wing pads and are going to form wings. If the majority are winged or are forming wings, they will leave the plant, and perhaps the field, and an insecticide application may not be necessary. Also, brown colored aphids are either dead or will soon die, so do not count them.
August is a critical
month for soybeans so its important to protect those good potential yields out
there, especially with the price of beans today.
How long will we need
to scout and manage soybean aphids? In SP-247
Soybean Aphids in
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
trial results on aphids can be found at http://www.ipm.iastate.edu/ipm/icm/2006/1-23/insecticide.html.
See the latest
Asian Soybean Rust
X.B. Yang now predicts
that there is a greater than 50% chance that
Soybean Sudden Death Syndrome
Soybean Sudden Death Syndrome (SDS) began to show up in some fields over three weeks ago and is becoming more evident as the season progresses. Fields that were flooded earlier in the season and fields south of Highway 92 seem to be most severely effected. While nothing can be done at this point for the 2007 crop, be sure that future soybean plantings are done with a variety that has as low a susceptibility to SDS as possible. Also, where there is SDS there is usually also soybean cyst nematode (SCN), so if the field has never been scouted / tested for SCN, it definitely should be. For more information on SDS, see pages 70 72 of the March 26, 2007 Integrated Crop Management (ICM) Newsletter or http://www.ipm.iastate.edu/ipm/icm/2007/3-26/bsr_vs_sds.html. For information on examining soybean roots for SCN see page 192 of the June 25, 2007 ICM Newsletter or http://www.ipm.iastate.edu/ipm/icm/2007/6-25/scn.html, and for soil sampling for SCN, see page 246 of the October 9, 2006 ICM Newsletter or http://www.ipm.iastate.edu/ipm/icm/2006/10-9/scn.html.
White mold is also showing up in some soybean fields, especially those with a heavy white mold incidence in 2004 (corn-corn-soybean rotation). Nothing can be done for the 2007 crop, but the next time soybeans are planted in the field, plan to use good white mold management techniques. Information is available from the North Central Soybean Research Program at http://www.planthealth.info/whitemold_basics.htm; be sure to use the links on the left side of the screen.
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 p.m.
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 trainings are the ones
Fall Field Day
September 6, 2007 - 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. Watch http://www.extension.iastate.edu/Pages/eccrops/meetserc.html.
If you have any questions, please feel free to contact the Iowa State University Extension Office.
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