Issue No. 14, Article 4/June 24, 2005
The Soybean Aphid Watch Continues
People throughout the Midwest continue to monitor soybean aphid popula-tions, and we have not witnessed much of an increase in densities from last week (June 13) to this week (June 20), at least not in Illinois. However, I will share with you the information we gathered, as well as reports from others, to keep you up to date.
On June 20 and 21, a pair of our summer employees scouted for soybean aphids in 18 fields in eight primarily northeastern and north-central Illinois counties (Boone, Ford, Grundy, Kendall, Kane, LaSalle, McHenry, and Winnebago). They are using the speed scouting method developed by entomologists at the University of Minnesota (http://www.soybeans.umn.edu/crop/insects/aphid/aphid_sampling.htm). Using this method, scouts discontinue sampling in a given field after 11 plants have been examined if the number of infested plants (defined as plants with 40 or more aphids) is 6 or less. In all 18 fields examined, the number of plants with 40 or more aphids was less than 6 (i.e., indicating no need for treatment). The average densities among the 18 fields ranged from 0 to 13.5 soybean aphids per plant (total number of aphids counted divided by 11 plants sampled), well below published economic thresholds. Our guys found no soybean aphids in 4 of the fields they surveyed, and 6 of the fields surveyed had an average of 1 or fewer soybean aphids per plant. One field in Kane County had an average of 9.8 soybean aphids per plant, with a range of 0 to 34 aphids per plant. Soybean aphids were found on 10 of the 11 plants sampled. One field in McHenry County had an average of 13.5 soybean aphids per plant, with a range of 0 to 51 aphids per plant. Soybean aphids were found on 7 of the 11 plants sampled. Soybeans ranged from V3 to V7 in the 18 fields surveyed, and multicolored Asian lady beetles were found in 5 of the fields.
Other reports of soybean aphids in Illinois follow:
- An average of 1 to 3 soybean aphids per plant in 4 fields in Kendall County on June 21 (David Onstad, Department of Natural Resources and Environmental Sciences)
- A range of 0 to 6 soybean aphids per plant in 3 fields in Stephenson and Winnebago counties on June 21; 30% of plants infested in a field in Lee County on June 20, with a range of 0 to 25 aphids per plant (Jim Morrison, Extension crop systems educator, Rockford)
- 300 to 400 aphids on some plants in a soybean field (V4 soybeans) in Lee County on June 17, although the field average was relatively low (i.e., most plants not infested with many aphids). Many of the aphids on the heavily infested plants were alatoid nymphs, which will molt into winged adults (Jim Donnelly, Ag View FS).
Soybean aphids on soybean leaves in Lee County (photo courtesy of Jim Morrison, University of Illinois).
Soybean aphids on stem and leaves of a soybean plant in Lee County. Note the lady beetle and the ants (photo courtesy of Jim Donnelly, Ag View FS).
In addition to all of the soybean aphid sightings in northern Illinois, Ron Hines, senior research specialist at the Dixon Springs Agricultural Center, found some soybean aphids as well as spider mites and thrips on soybean plants in Pope County. The numbers were low (1 to 2 per trifoliolate), but their presence in a southern Illinois county at this time of year is worth noting.
We recently received notification that the U.S. Environmental Protection Agency (U.S. EPA) has granted Valent USA a federal label for Orthene 90S in soybeans. Also, Valent will be issuing a 2(ee) label to allow the use of
Orthene 90S at 0.56 lb per acre for soybean aphid control. The current federal label indicates a rate of 0.83 to 1.1 lb of Orthene 90S per acre for control of soybean aphids. This same range of rates includes control of bean leaf beetle and green cloverworm, among others. We have had no experience with the efficacy of Orthene against soybean aphids, so I can offer no comments. However, you should be aware of the label. If I receive any information about the efficacy of Orthene against soybean aphids, I will share it in a future issue of the Bulletin.
The soybean aphid watch will continue so that we will be able to detect any significant upturn in their densities. In the meantime, keep watching for their presence, and let us know what you find.--Kevin Steffey