Ronald Calhoun, environmental turfgrass specialist for Michigan State University, is filled with enthusiasm for the MSU GDD (growing degree day) Tracker and the resources it brings to the entire green industry, including sports field managers.

As noted on the Web site, “Growing degree day models use a base temperature for calculating biological activity on a given day. Base temperatures are related to the organism being tracked. For instance, insects are cold-blooded, and the base temperature for most insect models is 55 degrees. The base temperature will vary depending on the organism.”

Photos by Steve Trusty.
Shade patterns within a stadium impact temperatures, as well as light.

The GDD Tracker chart lists the minimum temperature, maximum temperature and average temperature. It includes the GDD for base temperatures of 32, 40, 42, 45 and 50 degrees; rainfall in inches; and the potential evapotranspiration. All of the data for these listings is given by day and date, along with the accumulated GDD totals.

According to the Web site, “One way to calculate growing degree days (GDD) is to use a simple average. In this method, you take the average temperature from a given day (low temp + high temp/2) and subtract the base temperature for the model you are tracking. If the result is less than zero, then the GDD total for that day is zero. If the result is greater than zero, then the result of the formula is your GDD total for that day. The models use cumulative totals to predict their target ranges. The GDD Tracker site starts recording on March 1 of each year. The GDD totals displayed for a given location will vary depending on the base temperature for each model and the target ranges for that model.

“Thus, if the base temperature is 50 degrees, and the average daily air temperature on a specific date was 58 degrees, the GDD for that date would be 8. For each day after that first listing date, the GDD numbers would be added together to give a total accumulative GDD figure.”

Calhoun notes that by basing predictions on growing degree days instead of an arbitrary calendar date, a customized report can be created for bug activity, crabgrass emergence, disease breakout and other situations in a specific area.

There is no charge to access the Web site or to sign up for the customized reports. To sign on, just enter your zip code and input the model you’d like to follow and at what level of that model you’d like to be alerted.

There are nearly 600 users spread across Michigan, eastern Wisconsin, the Chicago area, northern Indiana and Ohio. There also are some users in Pennsylvania and New York that are looking at a weather station that is close to their same latitude. They can compare their conditions to the recorded data and tweak it as needed to compensate for the different factors that impact local conditions.

Practical applications

The GDD Tracker initially started as a relatively low-level project, according to Calhoun. The intent was to gather enough solid data to track the timing for Embark applications, for seed head suppression on Poa annua, as a tool for golf courses in Michigan. He says, “It has quickly taken on a life of its own as turf professionals recognize how effective it can be. On that first project, we’ve tested Proxy/Primo tank mixes, as well as Embark, with various rates and timings based on the GDD. We can show which were most effective so turf professionals can plan their scheduling more precisely for the next year.”

Calhoun has tied the GDD Tracker data to broadleaf weed identification on the MSU Turf Web site ( Often weed activity isn’t identified until the weeds are in flower. Now you can go to the Web site, enter your zip code, and look at 10 weed flower pictures that would most likely be in bloom during a specific period. MSU is using the data collected to reassess much of the current weed control practices to more accurately target application periods.

For a broader picture of weather-related data go to the MSU Web site: for a listing of weather-based pest, natural resource and production management tools.

Wear patterns, such as this one at the front of the bleachers bordering the field, affect soil temperatures and should be considered when planning field maintenance procedures. Soil and surface temperatures may vary from general field temperatures in those sections bordering synthetic fields, rubberized running tracks and paved surfaces.

Looking ahead

The second full-state launch of the GDD Tracker will take place in Indiana, starting in March 2009, with Purdue as the cooperating university. Calhoun says, “The program should be workable with little tweaking for the areas of all the Big Ten universities, as well as Nebraska, Iowa and South Dakota. It’s fairly easy to have a cutoff point with these areas because of the cold winter temperatures.”

In addition to the statewide weather stations listed on the Web site, the program is getting additional data from six GDD weather stations that they purchased and set up in other states. There is one cooperating site in eastern Wisconsin, northern Ohio, Indiana and Illinois, and two sites in Minnesota. The data is sent from these sites to MSU to be plugged into the system for comparison. Those six stations are portable, so they can be moved to different sites to be sure of the data points. This information can be used in mapping conditions, much as the National Weather Bureau does when using data surrounding a “hole” (or area with no data feedback) to draw the lines for fronts or other weather patterns.

The same basic GDD Tracker concept would be workable at other sites, but would need adjustments for factors such as climatic pockets, like ocean moderation in the East, and for cutoff and start-up points in moderate temperature zones.

Calhoun says, “Another part of the system is the flashback. You can hit that button and it will redraw the map to show what the temperatures were one year ago on that day. You can tell if it was hotter or colder or about the same. There’s also a slider you can use to look up what the National Weather Service is predicting for up to five days into the future. That’s temporary information taken from the temperatures on their weather map. The predicted values will be replaced with the actual data as it become available. But the predictions can be helpful if you’re trying to determine the timing for a specific procedure that is very close to being beyond the temperature range for effectiveness.”

MSU is also looking at gathering cooling degree day data. Calhoun says, “Cooling is the exact opposite. We take the same temperatures and take the average of the cool nights to determine how much the soil temperatures are cooling down. We want to be able to quantify that from August 15 into November to assess where the peak is for the fall series of applications, such as broadleaf weed control, fall fertilization and seeding.

Calhoun notes that the GDD Tracker is not an arbitrary system that tells you what you must do and when you must do it. Instead, it’s a tool in the arsenal that helps you more precisely fine-tune your management program.

The author is a contributing editor for SportsField Management.