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GDD Calculator

Discussion in 'Pesticide & Herbicide Application' started by tremor, Oct 26, 2002.

  1. tremor

    tremor LawnSite Bronze Member
    Messages: 1,476

    I have a Growing Degree Day calcualtor (Excel based) that was built for Ag use. With some help, we can rebuild it for T&O use.

    Who wants in?

  2. RMDoyon

    RMDoyon LawnSite Member
    Messages: 230

    Okay I'll bite.
    What is a Growing Degree Day?
  3. tremor

    tremor LawnSite Bronze Member
    Messages: 1,476

    It was quicker to steal this definition than I could type it.

    Please keep in mind that this is a sterile definition of the term, but one can see the relevance & how we can use this data to accurately predict everything from when Chinch Bugs will begin to show and crabgrass will germinate to (with accurate input data) the time of day that Gypsy Moth Catepillars will hatch.

    Heating days are not if interest to us. That's for the use of energy providers and large scale fuel consumers (though commercial greenhouse operators would find it useful).

    The calculator I have requires a minimum of 2 daily entries. The high & low temperatures. It makes adjusyments for different crops & pests, which is why I think it will be useful for Turf & Ornamental pest prediction. For my own purposes, I have added cloud cover, humidity, soil temerature, & precipitation data points.


    Degree days are computed from each day's mean temperature (max+min/2). Each degree that a day's mean temperature is below or above a reference temperature is counted as one degree-day. The amount of fuel necessary for home or industrial heating is indicated by the mean temperature for that day. Estimates are that most people use their furnace when the mean daily temperature drops below 65F.

    Heating degree-days are determined by subtracting the mean temperature for the day from the reference temperature. Thus, if the mean temperature for a day is 50F and the reference temperature is 65F, there would be 15(65-50) heating degree-days on this day. On days when the mean temperature is above the reference temperature, there are no heating degree-days. Therefore, the lower the average daily temperature, the more heating degree-days and the greater the consumption of fuel.

    Cooling degree-days are used during warm weather to estimate the energy needed to cool indoor air to a comfortable temperature. Mean daily temperature is converted to cooling degree-days by subtracting the reference temperature from the mean. For example, a day with a mean temperature of 80F and a reference temperature of 65F would correspond to (80-65), or 15 cooling degree-days. Higher values indicate warm weather and result in a high power production for cooling. Knowledge of the number of cooling degree-days in an area in the summer gives power companies a way of predicting the energy demand during peak energy periods. A summary of heating and cooling degree-days can give a practical indication of the energy needed over the year.

    Growing degree-days are used as a guide to planting and for determining the approximate dates when a crop will be ready for harvesting. A growing degree-day is defined as a day on which the mean daily temperature is one degree above the base temperature-minimum temperature required for growth of a particular crop. For sweet corn, the base temperature is 50F and, for peas, the base temperature is 40F.

    The mean temperature on a summer day in Iowa might be 80F. If the base temperature for beans was 50F, then the beans would accumulate 30 growing degree-days. Theoretically, beans can be harvested when it accumulates a total of 1200 growing degree-days. So, if beans are planted in early April and each day thereafter averages about 30 growing degree-days, the beans would be ready for harvest about 40 days later, or around the middle of May. Although moisture, variation of temperature and other factors are not taken into account, growing degree-days serve as a useful guide in forecasting approximate dates of crop maturity.
  4. KenH

    KenH LawnSite Bronze Member
    from CT
    Messages: 1,622

    Id be interested. I 'used' to call the Ag station for updates, but as you can imagine, it became tiresome and I wasnt always on top of it.
  5. tremor

    tremor LawnSite Bronze Member
    Messages: 1,476


    Send me an email to:


    I'll keep a list for a few days to see who else wants in. Then I'll forward everone the program.

    Beware! It's a big file & it does contain macros....my antivirus program went nuts when I got it. LOL

    First make a list of pest targets we want to install. Then we'll need the Degree Day data to input for each pest. This is where I really need help. I haven't found a single source for all the data needed. But if a half dozen of us each volunteer to contact our local ag or turf science school we can move ahead more swiftly. Obviously all volunteers will have to "own a portion of the list". It will do no good to have 6 people all looking up the same thing & have no one looking up another.

    Once all the items are installed, it might be possible to post the data here for daily lookups.

  6. GroundKprs

    GroundKprs LawnSite Bronze Member
    Messages: 1,969

    Great mind tickler, Steve. This is copied from an older post :

    The observance of temperatures is essential to understanding the activity of nature. The temperature model of most interest to me is the growing degree day model. I will type "GDD50" or "gdd40" here, because I do not know how to type subscripts, but you will almost always see the "GDD" or "gdd" followed by a subscript number. This number is the baseline temperature for the model used in the writer's data. GDD's are modeled for different plants, and for different areas of the country, so you will see different baseline temperatures used. This idea of GDDs has been used for a long time in agriculture in our country. Where I am we generally use GDD50 for landscape plants.

    To understand the idea of growing degree days, please first read <a href="http://www.wunderground.com/about/faq/degreedays.asp">THIS PAGE</a>. Later you may wish to search for much more info by a search in Yahoo or Google for "growing degree day."

    The life stages of many plants and insects have been tracked and recorded in relation to GDD. So one can anticipate the flowering of a certain plant, or the hatch of a certain insect, if they are aware of the current GDD figure for their area. I have established an average GDD accumulation based on NOAA historical data for our area, and enter this year's data to anticipate activity in the current season. I just enter each day's high & low temps into a file, my database does the calculations. For example, last year we had a terrific warmup, and then sustained heat for a while; I knew things would start to happen earlier than normal:

    1- on 4/21, the average historical temps give 1 GDD, and in 2001 it was 109 GDD (this is not unusual, because average historical temps tend to give a lower figure in the beginning of the season.)
    2- on 5/10, historical GDD= 78.0, 2001 GDD= 352.5 (this figure historically reached on 6/3 =>certain things are gonna happen 4 weeks earlier than normal!)
    3- on 5/31, historical GDD= 312.0, 2001 GDD= 535.5 (this historical figure usually reached on 6/13 => things have stabilized a little, but still 2 weeks ahead of normal.
    4- state extension data tells me that 2nd generation of euonymous scale hatches around GDD50 = 1300, which historically occurs on 7/18-19; this year on 7/13 GDD50 was 1289. If I waited for the usual time, I would have missed optimum control window by a week.

    While most of my examples are in ornamentals, not turf (but there is so much more happening in ornamentals - lot more fun!), there are also applications to turf maintenance. Dandelion leaves grow a waxy coating to overwinter. Even when they start to grow in the spring, this wax prevents absorption of herbicides to some degree. Ever do that early spray and just burn off the leaves, and had to re-treat later? That was because not enough herbicide was absorbed to get to the root. If I am tracking GDD50, I know in our area that I can expect control using an ester formulation after GDD50=80, and after GDD50=110 (or is it 130? - couldn't find notes) I can use amine herbicides with good results. You will often see data on turf referring to soil temperatures, with temps measured at a certain depth. These uses are usually in reference to root infecting diseases, because they operate in the soil medium. Discussions of other turf problems refer to ambient (air) temps, especially for diseases that operate above ground, infecting the grass leaves.

    Got more I could say, but don't have time. Search your own extension website, visit your county cooperative extension officer, and see if your state has GDD models for you to work with. Along with GDD, knowledge of phenology is neat: learn how to manage microclimates - areas, usually sheltered from normal environmental influences, that can have actual GDD a month ahead of or behind the rest of the outdoors in your area.
  7. tremor

    tremor LawnSite Bronze Member
    Messages: 1,476


    You're no stranger to this. Can I count you in?
    I have it set at GDD40 & GDD50 now. Very easy to copy in additional columns for added flexibility.
    It will require input for all concerned areas. In other words, what is accurate here in southern CT, won't be for Ken in Central CT. Yet it might work fine for you in IL just by coincidence, but only at certain times.
    This is why we need many people working on the model. Even then, there will be gaps in accuracy.

    I'd like to build this thing with the help of several people who all have some experience with the concept. After it's all set up, we can share it with anyone who want's it.

    It will be up to individual users to keep their own document current. If they do, the data will provide fairly accurate predictions. If they don't, then it's useless.

    Are you in?

  8. GroundKprs

    GroundKprs LawnSite Bronze Member
    Messages: 1,969

    Steve, on the calculation of GDD, a database is much simpler. You have to program all the cells of a spreadsheet for as long as you want to use it. You can easily have a database do the simple math calculations, design is a lot simpler, and you can use it a little or as much as you want. Unless you are wanting to specify different baseline temps; but even if you do want to use just 2 or 3 baselines, a database still wins.

    Only problem would be what database everyone would want to use. I suppose Excel spreadsheet is available to most. Could probably be written in Microsoft Works database, and imported to Access for those who use it.

    And temp data costs now. Used to be able to get official numbers from NOAA website, but now need to buy a yearly subscription to have access to all historical records. The information highway is becoming a toll road. :mad:

    Set mine up years ago in a simple flat file database (non-relational), just enter today's high & low, and you get today's GDD, year to date GDD, and comparison to historical GDD on this date.

    If you want, email me the Excel file, so I can see the functionality. GroundKprs@aol.com

    BTW, there are GDD calculators beginning to appear on web. Michigan State has one. I believe it is also a subscription service.
  9. ant

    ant LawnSite Silver Member
    Messages: 2,466

    i am in steve;i knew it won't take you long to post it...
    good job..

    i track min.-max. temp's each day here in southern n.j.

  10. grassguy_

    grassguy_ LawnSite Senior Member
    from Ohio
    Messages: 633

    Steve, I'm sure we can get data on the turf insect DD from Dr. David Shetlar at Ohio State. From My knowledge he's kind of perfected this DD knowledge for many grubs and surface insects. I'm not sure what his website is but ill track about and see if I can come up with some info on it.

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