About GDDTracker 4.0

What is GDD?

Growing Degree Days (GDD) are a measure of heat accumulation used to estimate the growth and development of plants, insects, and schedule applications such as crabgrass preemergence herbicide and plant growth regulators. GDDTracker calculates GDD using the simple average method where a base temperature is subtracted from the mean daily temperature. GDDTracker starts counting GDD on February 15. GDDTracker has several models using different base temperatures based on turfgrass research.

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Poa annua Seedhead Suppression with Proxy/Primo

At-a-glance: Base Temperature: 32 degrees F, Target GDD Range: 200-500, Source: Calhoun - Michigan State University (2004)

As the rain falls, temperatures rise and the grass gets greener our thought turn to properly timing Proxy/Primo tankmixes on creeping bentgrass/annual bluegrass turf stands. Current thinking from MSU, based on the recent success and failures, suggests that superintendents wait for two mowings after full green-up or 200-250 growing degree-days on the GDD32 degree-day model. Results from 2003-06 showed greater success when the initial application was made earlier. We had declining results with each initial timing between 309 and 548. Best results in 2004 were with the 309 initial timing and decreasing slightly with each of the following initial timings. The results from 2005 indicated that even earlier initial timings were more effective. The second application should be made 21 days after the first. In nearly every case, two applications has performed better than one. Do not apply until all after full green-up.

Greens: Proxy/Primo tankmixes for greens should be made at 5 + 0.125 fl oz. per 1000 square feet. Repeat applications can be made 21 days later. If you plan on using Primo throughout the season you can start your program 14-21 days after the tankmix treatment.

Fairways/Tees/Approaches: Research at MSU strongly suggests using 0.2-0.25 fl oz. of Primo with 5 fl oz. of Proxy per 1000 square feet. Tankmixes that contained lower concentrations of Primo (i.e. 0.1-0.15 fl oz) have not performed. Tankmixes of Proxy/Primo at 5 + 0.25 fl oz. per 1000 square feet provided seedhead suppression and turfgrass quality equal or better than all other treatments in 2003. Tankmix treatments that included the reduced rate of Proxy (3 fl oz.) did not perform quite as well as the full rate treatments but were still comparable to the Embark treatments in 2002 and 2003. If Proxy is used at reduced rates it may be necessary to apply a second application 21 days later. The label currently suggests using 5 fl oz. followed by 3 fl oz. This approach was used with good success at the MSU west course in 2004. Overall the results from 2004 were disappointing, however, results from the same applications in 2005 were generally favorable.

Does it work? What should I expect? The main advantages of the Proxy/Primo tankmix are the saftening of the Primo on the annual bluegrass and the alleviation of the Granny Smith green color associated with Proxy on the bentgrass. There also seems to be some synergism with regard to seedhead suppression. Primo provides only a delay in seedhead expression when used alone. Although Proxy will reduce seedheads, tankmixes have provided better seedhead suppression than Proxy alone. Typical results from this program are a 40-45 percent reduction in seedhead production during the spring flowering pulse.

Poa annua Seedhead Suppression with Embark (GDD22)

At-a-Glance: Base Temperature: 22 degrees F, Target GDD Range: 680-1050, Source: Calhoun - Michigan State University (2010)

Embark is very effective at limiting Poa annua seedhead in the spring. However, significant turfgrass injury (yellowing) can be associated with Embark applications (particularly on Kentucky bluegrass surrounds and roughs). Although the label lists rates of 4-6 fl oz per acre, most people are in the 3-6 fl oz per acre range. Embark injury can be exacerbated when frost events occur within two weeks after an application. Injury symptoms can be masked by tankmixing with a fully-chelated iron source. In nearly a decade of trials conducted by Michigan State University maximum seedhead control and minimum turfgrass injury can be achieved when Embark is applied between 680-1050 GDD on the GDD22. Applications made in this range will result in greater than 95 percent seedhead free surfaces.

Greens: Embark T&O is labeled for use on putting greens. The application rate for Embark T&O are 10X more than for Embark 2S. Use extreme caution to make sure you carefully read the label to make sure which product you are using. Embark T&O is typically applied at 30-60 fl oz per acre. It should be noted that control will decrease as the rate decreases. Split applications may be used on a 14 day interval not to exceed a total of 60 fl oz per acre. Kentucky bluegrass/perennial ryegrass surrounds will be injury by over spray. Take appropriate measures to minimize over spray on surrounds.

Fairways: Many superintendents use Embark for the control of Poa annua seedheads on fairways because some transient discoloration is tolerable and the cost per acre is much less than the Primo/Proxy tankmix. Embark 2S is typically applied between 5 and 8 fl oz per acre on fairways.

Does it work? What should I expect? Embark is the gold standard for Poa annua seedhead suppression. The product cost per acre is relatively low and the effectiveness is quite high. Some severe discoloration can occur when the product is over applied. Injury can be exacerbated by frost events within the first 10-14 days of application. Cool temperatures following injury will extend the duration of visible injury. Proper timing is very helpful to minimize injury and maximize effectiveness. Typical results from this program are a 75-85 percent reduction of seedhead production during the spring flowering pulse.

Poa annua Seedhead Suppression with Embark (GDD50) - no longer used.

At-a-Glance: Base Temperature: 50 degrees F, Target GDD Range: 25-60, Source: Danneberger, Vargas - Michigan State University (1983)

This model is no longer recommended; it is provided for reference. In four of six years this model overestimated a few warm days early in the season. Due to the higher base temperature and low number of GDD units necessary to reach the target, this model can quickly pass through the target range. Conversely, in cooler weather, this model in unable to account for biological activity that is occurring. Users are encouraged to use the GDD32 model featured on this site.

Poa annua Seedhead Flush (GDD22)

At-a-Glance: Base Temperature: 22 degrees F, Target GDD Range: 1050-2900, Source: Calhoun - Michigan State University (2011)

This model predicts the spring flowering pulse of Poa annua. The target range for this model covers the heaviest flower production pulse in the spring of the year. More work needs to be done to find an appropriate start date for this model in the southern portion of the GDDTracker user range. This model has not be ground-truthed in the southern parts of Illinois, Indiana and Ohio.

5086 (GDD50) - no longer used.

At-a-Glance: Base Temperature: 50 degrees F, Target GDD Range: Various

The 5086 model is one of the oldest GDD models used by biologists and agricultural practitioners. The 5086 has both a base temperature (50 degrees F) and a ceiling temperature (86 degrees F). This model is provided for convenience for individuals wishing to track GDD using these parameters.

Crabgrass Preemergence Timer (GDD32)

At-a-Glance: Base Temperature: 32 degrees F, Target GDD Range: 250-500, Source: Calhoun - Michigan State University (2004)

Proper timing of preemergence herbicides is critical to successfully suppressing summer annual grasses like crabgrass, goosegrass, and foxtail. These grasses need the proper soil temperature and soil moisture to germinate and establish. Eighty percent of the germination will occur when the 0-2 inch depth soil temperature is consistently reaching 60-70 degrees F. Preemergence herbicides need to be applied before the soils reach this optimum range. Therefore this model uses GDD to indirectly measure soil temperatures in a turf situation. As with all the models, discretion and understanding of local conditions should be considered. The target range for this model attempts to predict when the 0-2 inch depth soil temperatures consistently reach 50-55 degrees F and therefore provided adequate time for the preemergence herbicide to be incorporated before germination occurs.

More info: https://www.canr.msu.edu/news/timing_crabgrass_pre_emergence_applications

Crabgrass Germination Timer (GDD50)

At-a-Glance: Base Temperature: 50 degrees F, Target GDD Range: 200-600, Source: Calhoun - Michigan State University (2004)

This model correlates GDD accumulation with data from MSU field trial where dataloggers monitored soil temperature in the spring, before, during and after the main germination period of crabgrass. This model can be used to verify preemergence performance and as a trigger to conduct scouting (south-facing slopes, knolls, sidewalk edges, bunker faces).

Dollar Spot Suppression with Early Season DMI Application (GDD50)

At-a-Glance: Base Temperature: 50 degrees F, Target GDD Range: 140-175, Source: Dwyer and Vargas - Michigan State University (2004)

Recent studies at MSU have shown promising results from an early application of a DMI fungicide for suppressing dollar spot later in the season. This was first reported by Dr. Phil Dwyer at the 74th Annual Michigan Turfgrass Conference. Research into the mechanism of activity and refining the application timing has been continued by Ron Detweiler and Nancy Dykema in Dr. Vargas' lab.

Purdue Broadleaf Timer (GDD50)

At-a-Glance: Base Temperature: 50 degrees F, Target GDD Range (Ester, Ester/Amine, Amine): 110-150, 150-200, 200-600, Source: Schleicher, Throssell, Reicher, Weisenberger - Purdue University (1995)

Proper timing of herbicides is critical to good control. Broadleaf weed control is best accomplished in the fall of the year. However, the spring provides a opportunity to reduce broadleaf weeds at a time of year that we typically have more enthusiasm for such endeavors. In cooler temperatures, amine formulations will be less effective than their alcohol-base ester cousins. Using and ester formulation early in the season will provide better results. However, later in the spring, as landscape plants are flowering and air temperatures are warmer, ester formulations should be shelved for amine formulations. Amines will work better later in the spring with less potential volatility on a warm day.

Broadleaf Weed Flowering (GDD50)

At-a-Glance: Base Temperature: 50 degrees F, Target GDD Range: Various, Source: Calhoun - Michigan State University (2006)

This model predicts the relative flowering times for broadleaf weeds in the lawn and landscape. Understanding the lifecycle of a plant is helpful in developing a cultural management plan. Herbicide applications are unnecessary and ineffective on annual weeds that are flowering (as they are completing their lifecycle and will soon die with or without your help). It is helpful to be aware of what plants are currently flowering (i.e. early spring flowering is likely to be a winter annual) to avoid making these ill-advised applications. Conversely, flowering of perennials may represent a reasonable time to try and eliminate them with a broadleaf herbicide application. This model uses observed data from Michigan to predict the relative flowering times for winter annuals, summer annuals, biennials and perennials common to turf and landscape sites. You can read more about turf weed management at https://www.canr.msu.edu/turf/weeds.

Feedback to improve the site or add features

The team at GDDTracker.net looks forward to hearing from you. It will be your input that will help us improve the functionality of the site in the future. If there is a feature you would like to see added or changed, odds are, it would make the site more helpful and easier to use. Communicating your ideas with the GDDTracker.net team will allow us to incorporate them into future versions of the site.