Growing Degree Days – The Under Utilized Management Tool

The seeding season is beginning to wrap up for a large number of producers across western Canada.  But wait, there’s still an important step in setting yourself up for a successful growing season. Today we look at the importance of accurate seeding date records and how growing degree days can help you develop a management schedule.

Seeding doesn’t spare much time for notes and observations, but without complete seeding records you are setting yourself up for a less effective scouting season from that point on. So before it’s too late make sure to document your seeding records while it’s fresh in mind. In 2015, we’ve made that a bit easier: just head over to My Farm Manager where you’ll find a new seeding widget on the Fields page.  The new seeding widget also lets you adjust seedable acres, improving the accuracy of total yield and resulting profit reports.

OK, so now that you’ve got your seeding records in order, let’s look at how seeding date, weather and soil temperature notes are utilized.

At the basic level, seeding info is going to help you determine which fields to scout first. Of course this can be taken a step further: the real efficiency comes from one of the most under utilized tools in western Canadian agriculture; growing degree day (GDD) calculation.

Calculating growing degree days is based on this simple formula:

Daily GDD = ((Tmax + Tmin) ÷ 2) – Tbase

For example a day with a high of 24 and a low of 8 and 5 degree base would accumulate

((24+8)/2)-5 = 11GDD’s

The ability to predict a specific crop stage, relative to insect and weed cycles permits better management cycles and a allows for a more timely response to potential issues in the field. This is especially important when several different crops are being grown, each with a different management schedule for herbicide application, insect/fertility management and harvest.

If we know wheat first emerges around 125GDD’s and moves into 2 leaf stage around 170GDD’s then we can effectively gauge when to scout for cutworms, stand establishment counts and potential fertilizer injury. This capability loses its accuracy if seeding date is not accounted for.

There are a number of websites that allow you to look at how many GDD’s have accumulated through specific points in the season (see below), including data from previous years. For example, www.farmzone.com or http://weather.gc.ca.

So, if you know historically that from June 15th to July 2nd your area get 80GDD’s, or you estimate from your 14 day forecast, then you can add that number onto your already accumulated GDD’s to help determine when you will need to line up a custom sprayer for your fungicide application, or even whether you can plan to be away for the weekend to watch your kids baseball game.

Seeding date is also crucial in conjunction with GDD’s if you are trying to better understand yield variations in any trial work you are doing.  Ever had a year where you had an early frost that caused grading or yield loss? Are you working on managing maturity? If you utilize GDD’s in conjunction with seeding records over multiple years, you can better identify the practices, products or varieties that decrease time to maturity and effectively mitigate risks to your production.

There are a number of ways beyond the above-mentioned uses for GDD’s to be effective on farm. What are some ways you have strategically used GDD’s (or similar tools) to benefit your operation? Do you plan on using this tactic this year? Leave us a comment and let us know!