Predicting Corn Herbicide Application "Windows"

June 4, 1997 4(11):74-75

Joe Lauer and Chris Boerboom
Corn Agronomist and Weed Scientist

The cool growing season we have had so far during 1997 has slowed corn emergence and consequently changed the normal timing for some our management decisions. The decisions most influenced by the cool growing year are postemergence application of herbicides. Table 1 describes the projected last dates for application of herbicides based on the growth and development model published in the Wisconsin Crop Manager on May 22, 1997 (4(9): 58-59), the Growing Degree Units accumulated thus far, and the 30-year average for temperature at Madison, WI. In this table, postemergence herbicides have been grouped to approximate the corn growth stage. The maximum labeled growth stage for these herbicides may not exactly coincide with these corn V-stages but should be close. Keep in mind that these are only projected windows for herbicide application. These projections are subject to weather fluctuations. Also, keep in mind that there are numerous other factors that go into a herbicide application decision such as weed size at the time of application. Because of the cool temperatures this year, weed size and development may be greater than normal compared to corn. Always follow directions on the label.