Why Growing Degree Days Are Critical to Crop Health

Tracy Pell

May 31, 2018

Every year on the farm seems to bring different weather conditions. Early season heat accumulation or growing degree days (GDDs) greatly affect crop growth, but a shift in the weather in early July or August can drastically alter trajectories. 

Why Do Growing Degree Days Matter?

Growing degree days matter because GDDs help predict when a crop will reach maturity.

Total GDDs over a crop’s growing season are about plant development and the accumulation of heat needed to reach maturity. When soybeans are planted later than May 20, you could experience a loss in soybean yields due to reduced GDDs.

While early planted corn is at the two leaf stage, the first nodal roots have begun growth from the top of the mesocotyl and are now providing the majority of nutrition to the seedling corn. The seminal root system (those roots growing from the seed) end their growth, but will continue to contribute small amounts of nutrition to the corn plants until crop maturity.

Healthy crops that are on target with GDDs are able to reach maturity faster, and better battle stress and pressure.

Strong Plants Can Better Battle Bugs

A corn plant will grow an additional two leaves per week at this stage of growth with normal temperatures and adequate moisture. In the earliest planted soybeans, from VE (emergence) to V1 (first node/unifoliate leaf), soybean cotyledons feed the plant until the unifoliate leaves emerge, which is why it is important to protect the cotyledons from insect damage.

Bean Leaf Beetle (BLB) feeding has been reported by Nebraska farmers, and a few soybean fields have reached treatment levels. Nodulation (nitrogen fixation) will begin soon in normal temperatures. Be sure to carefully examine soybean roots to locate the small nitrogen nodules that are attached to the roots.

If you haven’t already begun your weekly scouting, you’ll be underway soon. Stay focused on early season insects and weed escapes. Be prepared to rescue treat your crop if necessary, and consult with an extension agronomist. Review any product label before you make an application.

Help Plants Keep Up

There’s not much you need to do at this stage, if you are concerned about being behind on GDDs. But you can think through a few steps to keep crops healthy, strong and growing throughout the season—make in-season fertility treatments to feed crops at critical growth stages, and protect them from fighting weeds for critical nutrients or dealing with disease or insects.

With that in mind, here are few product-specific and mode-of-action-timing restrictions to remember when making post-emergence herbicide applications in corn.


Timing Restriction in Corn


12 inch corn


to 48 inch corn

Mesotrione (Callisto®)

8 leaf or 30 inches


6 leaf collars


8 leaf or 30 inches

Halex® GT

8 leaf or 30 inches


up to 45 days before harvest


36 inches

As always, be sure to read and follow label use directions and check out our guide to getting the most out of your chemical applications for more information

This information should not be used as a replacement for consulting the applicable product label. Please consult the label for the most complete and up-to-date information about any referenced product. Readers must have a valid applicator license to use restricted use pesticides. Please consult your state department of agriculture for complete rules and regulations on the use of restricted use pesticides as some products require specific record-keeping requirements.

Status® is a registered trademark of BASF Corporation. Capreno® is a registered trademark of Bayer. Impact® is a registered trademark of AMVAC Chemical Corporation. Callisto® and Halex® GT are registered trademarks of the Syngenta Group Company. Cadet™ is a trademark of FMC corporation.

Tracy Pell

May 31, 2018