By Kyoko Scanlon, Forest Pathologist, Fitchburg;
Kyoko.Scanlon@wisconsin.gov

With the recent warm-up and little snow on the ground in February, you may wonder if the insects responsible for transmitting oak wilt (oak wilt vectors) may emerge earlier this spring.

Though it is impossible to know precisely when they emerge, there is a tool that can be used to help you ease your anxiety a bit.

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

University of Wisconsin-Madison Division of Extension’s Oak Wilt Vectors Emergence Thermal Model can help predict when oak wilt vectors may be coming. / Graphic Credit: Wisconsin Extension

A unique online tool, developed in 2021 as a collaborative project between the University of Wisconsin-Madison and the Wisconsin Department of Natural Resources (DNR), 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 and actual weather data. This helps refine the beginning of the periods when pruning, wounding or harvesting oaks should be avoided.

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

Users can also sign up to receive a daily email notification of current and five-day forecasts based on the average daily high temperatures from the previous week. Please be aware that this forecast could be off significantly if the temperatures of the upcoming week differ significantly from the previous week’s average. The model is not based on the predicted daily high temperature.

Please note that this interface is intended to supplement, not replace, the calendar dates specified in the DNR’s Oak Harvesting Guidelines. This interface 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 questions about this interface, please contact your Regional DNR Forest Health Specialist or Kyoko Scanlon, DNR Forest Pathologist, at Kyoko.Scanlon@wisconsin.gov.