Extension Entomology Mail Mike Catangui, Ph.D. Associate Professor & Extension Entomologist
June 21, 2006 (Issue 060621)

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Time is of the Essence my Friends (Update 7-16-06)

I was at the SE Farm near Beresford today to check on our soybean and corn
research plots.

Soybeans at the SE Farm and most of the counties along I-29 and including
Brown County are now in full bloom or R2 stage.

The most interesting report came from our crew that aphid numbers are high and
very early at the NE Farm near South Shore this season.  We have never found
high numbers (up to 1500 on some plants) of soybean aphids at the NE Farm.
Buckthorns are absent for the most part in Codington County.

Thus, the theme so far based on numerous reports from crop consultants, Extension
educators, coop agronomists, sentinel #rap plots, and our entomology crew, is that
soybean aphids are at least 2 weeks early this season, and that we are finding them
in areas not known for high infestations in the past.

As of today Friday July 14, 2006, soybean aphids have now been sighted in 16 counties.

Take action now.  You snooze, you lose.  It's your money for your kids.

Just to share a technique with you in sampling the aphids:  almost all of them are on
the newest fully-expanded uppermost trifoliate right now; we pluck 10 tender trifoliates
per 20 feet of row for a total of 30 leaflets per plot.  We then freeze the leaflets and
aphids for easy counting in the lab.  We pluck them ! That's it.

Alates From Buckthorn Still Flying (Update 6-29-06)

(Note:  Dr. Louis Hesler tells me that the winged aphid above may actually be a cowpea aphid
Why was it on soybean?  Don't know yet.)

Winged aphids are still actively migrating from buckthorns, at least here in our
plots in Brookings, SD.

Also very close to producing alates are overcrowded colonies already on
nursery soybean plants.  The two alate forms may overlap in colonizing the entire
field.

I think that the steps are as follows:  1) Alates migrate from buckthorns into
soybean seedlings.  2) Alates arriving in plants close to ant colonies are cared
for and defended from natural enemies by worker ants (Lasius neoniger, Formica
neogagates, Myrmica americana, among others).  3) Soybean aphids in these
nursery plants become overcrowded within 2-3 weeks and start producing alates
of their own.  4) These nursery plant alates then invade the entire soybean field.

The importance of ants in rendering natural enemies inutile is quite clear to me.
Yes Buford, I used a fancy word inutile.
 

Numbers More Further Along in Brookings (Update 6-23-06)

                 

    This afternoon (Friday, June 23, 2004), I inspected our plots   
    here in Brookings, SD to see whether aphids were around.
    Boy, was I surprised.  The plants were merely V2 but aphids
    were already quite abundant (pictures above).  Myrmica
    americana worker ants were tending the aphids which were
    already reproducing viviparously.  What I find quite interesting
    is, first, V2 is quite early for an aphid infestation this big, and
    second, this is the first time that I have seen Myrmica americana
    tend soybean aphids.  I found this ant species quite commonly in
    open rangelands in western SD and ND.  As soybean aphid
    tenders, they were aggressive and defended the aphids well
    when I tried to touch the aphids.  And one last observation: there
    were no natural enemies in sight.  Donde esta ladybird beetle?
 

Soybean Aphids Already on the Field     

I looked at some soybean plants this morning in Crooks, SD on my daily commute to work.  Take
a look at them cute aphids already snug like a bug in a rug (pictures above).  They appeared to be
newly deposited by the winged aphids migrating from buckthorns.  The plants were still mainly V3
with a smattering of V4s.

Growers can start scouting the fields now and take action if necessary at R2 (full bloom) which is
merely 2-3 weeks from now.

I will regularly update this Web page as I traverse the vast expanse of soybean crops in the state.

In the meantime, you can peruse  http://plantsci.sdstate.edu/ent/entpubs/sa_ss_et_SD.htm
 

 . . . . Aphid Alert . . . . . Soybean Aphids in Brookings, Crooks, Tea, Yankton, Turner County, McCook County, Beresford, Davison County, Lake County, Charles Mix County, Brown County, Codington County, Hutchinson County, Lincoln County, and Kingsbury County . . . .       

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 Web Posted on Wednesday, June 21, 2006 by Mike Catangui. Last Updated on Wednesday, July 26, 2006.