July 26, 2004

 

CORN

Gray Leaf Spot

Gray Leaf Spot has shown up in some corn fields south of Highway 92 at levels not observed in nearly a decade.  It is generally unlikely that a fungicide application will be cost-effective when used in a timely fashion.  Looking at some of the fungicide options, Tilt and Stratego must be applied by silking at the latest at the onset of the disease, which eliminates both products at this point in the season.  Quadris only has a seven day harvest interval, but the label states to use it at the onset of the disease, which again eliminates it as being a viable option.  The bottom line is that it is best to just let it run it's course this year and emphasize gray leaf spot resistance / tolerance when selecting hybrids the next time corn is grown in the field.

Corn Rootworms

Corn rootworm pressure has been surprisingly high in 2004, resulting in many insecticide failures.  If you have not yet evaluated the performance of any rootworm insecticides used, now is a good time to dig up a few root masses, wash them off thoroughly with a hose, and inspect the roots.  To help you evaluate what you see, go to http://www.ent.iastate.edu/pest/rootworm/nodeinjury/nodeinjury.html.

SOYBEAN

White Mold

White mold is occurring at high levels in some fields along and north of I-80.  At this point in the season, there are no good management options.  In the future in those fields, the best management tactics are moving away from drilled or 15-inch rows back to 30-inch rows and selecting varieties with greater tolerance and/or less susceptibility to white mold.  In addition, an application of Cobra or Phoenix when flowering begins will help stimulate the soybeans immunity to white mold.  The fungicide Topsin is labelled for use on soybean and is effective against white mold, but the cost-effectiveness is questionable.  For more information, see Iowa State University publication 1731 "Soybean White Mold."

Soybean Aphid

Soybean aphid numbers remain generally very low.  However, the populations can explode very quickly, and the recent cooler weather may prompt that, so continue to remain vigilant.  Scouting and threshold information can be found on pages 66 - 67 of the June 14, 2004 Iowa State University Integrated Crop Management Newsletter or at http://www.ipm.iastate.edu/ipm/icm/2004/6-14-2004/soythreshold.html.

Bean Leaf Beetle

Bean leaf beetle numbers also continue to be generally low.  However, numbers in some fields, especially south of Highway 78, are approaching threshold, so, again, remain vigilant.  Scouting and threshold information can be found on pages 160 - 161 of the August 9, 1999 Iowa State University Integrated Crop Management Newsletter or at http://www.ipm.iastate.edu/ipm/icm/1999/8-9-1999/blbeffects.html.