View Full Version : GDD Calculator

10-26-2002, 11:11 AM
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?


10-26-2002, 01:51 PM
Okay I'll bite.
What is a Growing Degree Day?

10-26-2002, 02:53 PM
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.

10-26-2002, 05:01 PM
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.

10-26-2002, 05:30 PM

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.


10-26-2002, 05:40 PM
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.

10-26-2002, 06:00 PM

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?


10-26-2002, 06:13 PM
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.

10-26-2002, 07:23 PM
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.


10-26-2002, 08:14 PM
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.

10-26-2002, 08:44 PM

i will keep looking

10-26-2002, 08:45 PM
I have a few college textbooks which list many insects and the GDD's for each. I can send some over to give you examples. I will shoot you an email.

10-26-2002, 08:54 PM

10-26-2002, 08:57 PM

this is a good one for models

10-26-2002, 09:13 PM
are we supposed to be looking for models?

found this also;;;;; Though fall applications are most effective for controlling broadleaf weeds, spring applications are warranted for new lawns or areas that did not get treated last fall. Spring applications will be most effective if you wait until dandelions are flowering or at the puffball stage (but still not as effective as fall applications). Applications before mid-April will only "burn" the leaves and weeds will grow back by summer. We have found that growing degree accumulations with a 50 degree F base (GDD50) must be a minimum of 110 before ester formulations of 2,4-D are effective and 150 GDD50 before amine formulations are effective. Between 1/1/02 and 4/15/02, GDD50 accumulation in Vincennes is 260, Bloomington is 227, Indianapolis (Zoo) is 200, West Lafayette is 140, Bluffton is 105, and Michigan City is 99. Though degree day models provide an estimate, realize that many of these degree days were accumulated early in the spring and it still remains fairly cold throughout the state. Though control improves later in the spring, unfortunately so does the chance of off-site target damage to ornamentals, gardens, etc. Amines tend to be less volatile than esters thus reducing the chances for off-target damage later in the spring. To further increase efficacy, apply so the product will dry on the leaf for 24 hours or more before a rain, do not mow immediately prior to application to maximize leaf area, and do not mow for three days following application to allow the products to translocate

10-27-2002, 08:57 AM

This will be even more work than I thought it would.

So far, 4 of us are in. Ant, Grassguy, KenH, & ,myself.

Is that correct?

Ant, the last post you made is the data we need, but here's the catch, degree day threshold limits for each pest we'll likely concern ourselves with may vary by region. In other words, Haruo Tashiro claims 897-950 GDD45 for Chinch Bugs in Ontario, Canada as the threshold for chemical treatment where activity has been observed. This corresponds with the 3rd instart nymph stage at a times when most eggs have hatched but Adults haven't moved out of the target area. (quote from HTashiro's book, Turfgrass Insects of No.America & Canada)
As Jim/Groundskeeper has pointed out to me, this threshold point may vary for different cities.
For data collected in New Jersey by Mailloux & Streu 1981, GDD58.3*F was the degree day accumulation point where the egg hatch was COMPLETE by 115GDD58. We can work around this inconsistancy but it will take a lot more time.
It also points out the need for support from sources that have already collected field data for some period of time in a format that we're able to work with.
Via email, Jim also rightfully points to the fact that the data cells in the excel program I have are not "cell protected". So a misplaced key stroke, even once, will destroy the integrity of all results after the flawed data input.
Jim likes the idea of a database system. I agree with this. But if one currently exists, I still haven't found it. If available, it is probably through a chargeable subscriber service.

Turf diseases are going to be excluded in my preliminary version of the calculator. I am developing one for Pumpkins that includes humidity & precipitation data for one disease only. Powdery Mildew.
To establish these figures for every turf disease would require program writing that is way too complex for my level of computer literacy.



10-27-2002, 09:31 AM
DTN or Farmdata does it all for me. It already has the GDD for the whole region and it is updated everyday.

Don't see why need to tie up space on the one eyed monster.

Just my thoughts.

Call your local Extension Service. They must have a Pest News Alert. In KY they send one out every week and it covers Ag as well as turf. Give your local agent a call you may be suprised.

10-27-2002, 10:04 AM

Does Farmdata send it via email? Just a guess, but they probably don't cover the metro NY area due to low demand here. I could be wrong, so I'll check it out.

I checked on the files size too. The document takes up less space than an average jpeg image.

The idea is to make 2 data entries every day. Theoretically, from a $39.00 resttable, high/low thermometer that has been properly located in a permanant location at yout home or office. Or the user could pay for DTN or pickup the data from the newspaper or any number of free websites that provided the exact same doppler images that DTN broadcasts (but for free).

Our local ag station doesn't open until 9AM. Then you've got a little better than 50/50 chance of reaching voicemail. I check emails at 4:20AM every weekday. But I can't reach the ag station at that hour. When they get in, I'm either stuck in traffic or meeting with my first or second appointment of the day.

If this calculator works properly & the daily inputs are made, the prediction points are there all the time. It wouldn't take any longer than checking emails. I can't dial a phone number that quickly, let alone expect to get the info I'm after every single day. The ag station folks here are great. But I don't think they want me "checking in" once a week.

It's more than a little interesting that those of us who are interested in this are from major metro centers where ag has just about disapperaerd. Maybe you guys do have better quality ag station support than us metro guys. It seem the Metro Ag folks are too bust nattering with some landscape architect or "master gardener" on the rare occasion I pop in. The last 2 times I've asked for pathological help at Cornell Valhalla, I've ended up in New Haven. Both times Cornell was wrong. New Haven is great, but under staffed.


10-27-2002, 12:23 PM
For those in NY an closely surrounding areas ....

Also, there is AWS Weatherbug ... a small add sponsored program which sits in the taskbar and constantly updates current conditions and also advises of local weather alerts for your area.

10-27-2002, 01:53 PM
Be careful downloading weatherbug. I believe it is a type of spyware, with popups all the time. I had to take my computer to a tech to finally get rid of it.

10-27-2002, 02:15 PM

That is a useful link. But that is also the data that I already have.

The data that I still need is the actual degree day thresholds for the various insect pests that we deal with.

Once I have them all (I have BTA, Hyperodes Weevil, Hairy Chinch, & a few grubs) the document will be about finished. As long as the data doen't really vary by region. Thus the need for threshold data (not a running tally of recorded DD's) for each pest by region.

It's out there. Just scattered all over creation. Apparently no one has yet placed all the data in one data base.

That may be the only unique thing about this idea. LOL


10-27-2002, 06:07 PM
give me some time i will dig them up..

10-27-2002, 06:43 PM
the ones i found was for tree and shrub..if you wont i wlll post them.

10-27-2002, 07:22 PM
I have the weatherbug as well on my taskbar, also accuweather.com has the data from the Akron/ Canton Regional Airport which is very close to me. Surfing I found a few other GDD moels , but I think Ant has posted them earlier.

10-27-2002, 08:28 PM
Don't lose the Tree & Shrub stuff because that's next. I have a good start on Trees already, but we'll need more.

As of today I've located:
Bluegrass Billbugs, Hairy Chinch, Hyperodes Weevil, Masked Chafer Adults, Black Turfgrass Aetanius.

I'm going to go read Tashiro for a while tonight so I'll be snoozin' soon. But he's got a lot in his book.

I haven't gotten any weed data except for Dandelions. (I have never tried to kill a dandelion & failed though!!)


10-27-2002, 10:22 PM

10-27-2002, 11:50 PM
I apologize if I didn't read the begins of this thread completely, thus misunderstanding the overall intention.
If you need me to attemp to help locate some additional pest threshold info, just let me know which one you desire the most or are having the most dificulty in finding and I will do my best in the small amount of spare time that I have to find it.
Probably would have a lot more if I didn't spend so much time here ...
Well, have to run ... time to go to my LSA meeting again, coffee sucks but you can meet some nice people there...:drinkup:

10-28-2002, 09:06 AM

The lawn insects I have so far are in my last post.

We need all common Grubs except Masked Chafers.

We need all the Sod, Grass, & Southern Webworms.

We need all Cutworms & Armyworms.

I would like to include other insects that I may have little knowledge of, from areas to my south. Transition & south may harbor things I'm not aware of. We never see Crane Fly larva damage around here. But some of the members run into them.
Good DD threashold level data will include points such as

"In the spring, adult Hairy Chinchbugs emerge from winter harborage locations between 100dd50* (or 100GDD50) & up to 150dd50*. Third instar nymphs appear between 215dd50 & 235dd50 & are most succeptible to insecticide treatments at this time."
*** EXAMPLE ONLY (all made up- no truth to these numbers) ***

How the info is written (caps, abreviations etc) isn't important. Though the threshold data should be presented in Farenheight. I found & was already confused by some Celsius (centigrade) presentions. This can be converted, but it's not as easy as it sounds.

Different starting low temps like 45*F, 50*F, etc don't matter either. The program has different starting lows now.

I fear that some insects are behaving in an unpredictable patern & may not respond well to GGD paterning. This might explain the voids. I re-read most of Tashiro last night (...zzzzzzzzzz) & was surprised how little he discusses GGD's. But no explaination was offered for the omissions. He heralded Chinchbug DDG's as a fantastic means of predicition. Then never mentions it again in the next 100 pages. Go figure.

10-29-2002, 02:59 PM
im very new at all of these experiences but the data plan sounds like a great and very helpful idea. i think a lot of people would be able to plan every application easily

10-30-2002, 08:24 AM
I haven't taken the time to read each post in its entirety so I apologize in advance if it looks like I plagarized an idea.

NOAA calculates the GDD for corn all over the USA. RAther than make double entries everyday why not make a single entry daily or weekly. Since we know what the GDD is for corn all pests we want to track could be related to the corn GDD. If corn was 50 and pest x was 60 then a factor of 1.2 could be used in the formula.

I'm not super experienced in Excel. Can you write If/then type statements for one cell dependent on the values in another? The goal being a pop up warning or color code once certain GDD are reached for the target pest.

06-04-2006, 09:59 PM
Lets Kick This One Around..