Liz Bosak, Outreach Specialist, Department of Agronomy
Depending upon the herbicide, injury can occur after a pre-emergence application when corn is germinating in cool, wet soils. This year, if corn was planted in mid-April then you may observe some injury. However, it is important to remember that other environmental factors can mimic herbicide injury symptoms such as corn emerging in crusted or compacted soil. For this spring, WCWS has a re-designed online diagnostic tool, available at http://wcws.cals.wisc.edu/herbicide-injury-diagnostic-tool or from the main page http://wcws.cals.wisc.edu go to ‘Resources’ and then to ‘Tools’. The diagnostic tool asks three basic questions 1) When do injury symptoms appear? 2) Are both broadleaves and grasses affected or just one group? and 3) What are the symptoms and where do they occur? The original web-based tool was developed by Tim Trower and Chris Boerboom to accompany a handy two-page guide available at https://ipcm.webhosting.cals.wisc.edu/download/pubsPM/herbicideinjury_new.pdf. The following changes were made to the new version:
1. Each page shows your previous answers.
2. A ‘Start over’ button is located at the bottom of each page.
3. For each herbicide mode-of-action, an herbicide chart from the TakeAction poster available at http://takeactiononweeds.com/wp-content/uploads/sites/54/2014/01/herbicide-classification-chart.pdf or on the WCWS website under ‘Resources’, ‘Documents’(Fig. 1).
4. Simplified guides to symptoms that mimic herbicide injury during and after emergence are included on each mode-of-action page (Fig. 2).
5. Photo galleries for both corn and soybean injury symptoms are located on the same page (Fig. 3).
For pre-emergence applications in corn, the seedling shoot growth inhibitors, particularly the chloroacetamides, may injure seedlings when soils are cool and wet. Injury will not always be apparent aboveground. For example, corn plants with seedling root growth inhibitor damage will display clubbed root tips and grasses will be more affected than broadleaves. To get an idea of injury risk, check out the herbicide tables in “Pest Management in Wisconsin Field Crops” available in pdf and print formats at Cooperative Extension’s Learning Store, http://learningstore.uwex.edu/Pest-Management-in-Wisconsin-Field-Crops2015-P155.aspx.