August 22, 2019
Issue 9
Brown silk 2, 4-D.    Corn fields with broadleaf weeds escapes may benefit from a late season 2, 4-D treatment to reduce competition and future weed seed production. This treatment will help reduce seed production from sunflower and cocklebur - but is less effective on reducing velvetleaf seed production. Less is known about late season 2, 4-D effects on waterhemp seed production, but seeds that have already formed will likely be viable.
Late season cover crops. Flooded areas or prevented plant acres can still benefit from a late summer seeded cover crop

-          Oats will provide some cover, soil health benefits and will not overwinter.
-          Cereal rye or winter wheat will provide soil health benefits, will overwinter and will     need to be terminated next spring.
-          Brassicas - such as forage turnips or forage radishes will provide soil health benefits and will not overwinter.
-          All of these options will provide some potential for livestock grazing. An oat crop may provide some harvestable fall forage.
Corn Progress.   The Useful to Usable website (go to MRCC, view tools) uses to local information to predict crop development and crop maturity.   The following are some predicted dates with a 100-day hybrid planted in northwest Iowa. Black layer date on the June 5 planting will likely occur before October 22 since every day of planting delay reduces GDD requirement by 7 GDDs/day.
Plant date                    GDDs as of Aug 21/average     black layer date
April 26                       1965/2050                                September 16
May 7                          1925/1970                                September 19
May 16                        1870/1890                                September 23 
June 5                          1645/1605                                October 22
Soybean growth stages, soybean aphid. The soybean crop will be susceptible to injury from soybean aphids for the following amounts of time.
          Stage                      description                               days susceptible to aphids
R4                    ¾ in. pod at top 4 nodes                                    24
R5                    1/8 in. seed in pod at top 4 nodes                       15  
                        R6             full size seed in pod at top 4 nodes                   0-5 -depends on soil moisture
The economic threshold for treatment is 250 aphids per plant, more than 80% of the plants infested and aphid populations on the increase. Erin Hodgson explains the science behind this economic threshold in this ICM blog article .

Prepared by:
  Paul Kassel- Extension Field Agronomist


Phone:  (712) 262-2264


Serving Clay, Buena Vista, Dickinson, Emmet, Hancock, Kossuth, Palo Alto, Pocahontas, Sac and Winnebago Counties



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