By Kyoko Scanlon, Forest Pathologist, Fitchburg, Kyoko.Scanlon@wisconsin.gov or 608-235-7532

Oak wilt is a serious disease that occurs when insects carrying oak wilt fungal spores land on a healthy oak tree’s fresh wound. To prevent oak wilt infections, it is important to avoid pruning, wounding and harvesting oaks when these insects are abundant, generally from April through July. Predicting exactly when these insects start to emerge in the spring can be difficult as their emergence is highly weather-dependent, and spring weather varies significantly from year to year.

In 2021, the Oak Wilt Vectors Emergence Thermal Model tool, a unique estimation tool, was developed as a collaborative project between the University of Wisconsin-Madison and the Wisconsin DNR to help with these predictions. This online tool offers localized recommendations about the emergence status of the two most important insects that transmit oak wilt in Wisconsin. The interface uses a degree-day model (Jagemann et al., 2018) constructed from insect trapping data and actual weather data, which helps refine the beginning of the periods when you should avoid pruning, wounding or harvesting oaks.

UW Extension’s Oak Wilt Vectors Emergence Thermal Model can help predict when oak wilt vectors may be coming. Photo Credit: UW Extension

The tool runs on the UW Extension AgWeather website and is easy to use. You only need to enter two pieces of information on the homepage: your location and your date of interest. You can enter your location of interest by selecting the closest GPS coordinates from the drop-down menu, marking the location on the map or simply clicking “Get my location” to use your current location.

This online tool has received some significant improvements since its first development two years ago, thanks to Ben Bradford from UW-Madison, the web manager of the website. For example, you can now sign up to receive a daily email notification. Besides the current recommendation, the site provides users with the daily forecast for the next five days based on the average of the maximum temperatures from the previous week. This forecast is not based on the predicted maximum temperature for the following week.

Please note that this tool is intended to supplement, not replace, the calendar dates specified in the DNR’s oak harvesting guidelines. This tool provides degree-day-based information about the beginning of the oak wilt high-risk period, not the end of the high-risk period.

If you have any questions about this interface, please contact your Regional DNR Forest Health Specialist or Kyoko Scanlon, DNR Forest Pathologist, at Kyoko.Scanlon@wisconsin.gov.