Crops Bulletin

August 1, 2013  
 Issue 9 


Prepared by

Paul Kassel

Extension Field Agronomist



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



The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, national origin, gender, religion, age, disability, political beliefs, sexual orientation, and marital or family status. (Not all prohibited bases apply to all programs.) Many materials can be made available in alternative formats for ADA clients. To file a complaint of discrimination, write USDA, Office of Civil Rights, Room 326-W, Whitten Building, 14th and Independence Avenue, SW, Washington, DC 20250-9410 or call 202-720-5964.





Waterhemp Struggles Continue: Glyphosate continues to struggle to control waterhemp in many northwest Iowa fields. Herbicide options for waterhemp in soybean are limited.

  • Flexstar - 10 month rotation to corn, 45 day preharvest interval (PHI)
  • Cobra- 45 day PHI
  • Resource - 60 day PHI
  • Cadet - full flowering, 60 day PHI

Label guidelines for glyphosate applications limit amounts and timing. WeatherMAX/PowerMAX info is listed as an example - other glyphosate formulations are similar. Repeat applications of glyphosate are often ineffective where glyphosate failed earlier in the season.

  • 44 oz./a single, 64 oz./a total in-crop WeatherMAX/PowerMAX application
  • WeatherMAX/PowerMAX can be applied through the R2 full bloom stage

Therefore the remaining options are cultivation or hand removal. Of course, neither is very feasible for large acre farming operations.


Recent Cool Weather: Growing degree days (GDDs) have lagged about 50 units since July 23. This cool weather will be a benefit to hybrids that pollinated and began grain fill during this time period.   Seasons with below normal GDD accumulation in August (1994, 2004, 2008) have produced some very favorable grain yields.


However, late planted/replanted corn will continue to be at risk from decreased yield potential and early frost because of the cool weather induced delay in development.


Check Corn Fields for Rootworm:  Check corn on corn fields for rootworm control performance. Evidence of root damage and high numbers of corn rootworm adults indicate that rootworm may be resisting rootworm traits and/or insecticides. Dig and wash corn root systems and look for roots that are pruned back to an inch and half of the stalk.

Prepared by Paul Kassel, Extension Field Agronomist

Phone: (712) 262-2264, Email: