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Hello Debbie,

The GDD reading (Growing Degree Days ) is a calculation of accumulated air temperatures based upon daily readings of those temperatures.

Applying Pre-emergent for crabgrass control can be done by monitoring either one of two indicators—

1: when soil temperatures are consistently 50 to 55°F at a 2 inch depth.

2: or when base GDD 32 in your ZIP Code is between 250 and 500.

You can use the “Crabgrass PRE” tab on the right of the GDD Tracker map to determine when to apply pre- emergent for crabgrass. Enter your zipcode, then click Crabgrass PRE Tab. The map and charts will update for your zipcode.

Link to the GDD Tracker for 48114- https://gddtracker.msu.edu/?model=7&offset=0&zip=48114

From this MSU article, which you may already have— https://www.canr.msu.edu/news/timing_crabgrass_pre_emergence_applications

“keep in mind the range of the optimum application window extends from 250-500 GDD. You don’t have to apply the first day the model indicates…, but remember in most years we stay in the optimum application window for at least a couple weeks, if not longer”.

Scroll through the chart labeled “Tabular Data” to see the current date. This chart also projects a couple days out past today’s date.

On the tabular data chart use GDD 32 column for 2022( the left hand side columns of data) to determine how many degree days are recorded for your ZIP Code. For today 3/4/22 the GDD is 28 for ZIP Code 48114.

When the base 32 Growing degree days column reaches 250 it will be time to apply crabgrass pre-emergent. The map is color-coded, and when your area is ready or ideal to apply crabgrass preventer, that area of the map will be green.

The tabular data chart contains the 2021 years data in columns to the right so you can compare how warm or cold it is this year compared to last year. Be careful not to mix these two columns of data up.

Below I attached a screenshot of the GDD tracker set for your ZIP Code today. I marked it with red arrows to point out the areas I write about here

If you have other questions or need more help with this please do write again. If it is easier for you, you may speak with a Garden Expert over the phone at MSU‘s toll-free Garden help Hotline. The Hotline is open Monday, Wednesday, Friday from 9 AM to noon. The number<personal data hidden>.