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Thinking About Your Preemergent Herbicide Applications?

Tuesday, February 24, 2015   (0 Comments)
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Written by Pamela Sherratt and Dr. John Street, The Ohio State University 

Typically, March and April are the months depending on location in Ohio to apply preemergence herbicides in turfgrasss.

However, extremely cold weather to date has soil temperatures well below normal and soils are frozen in the upper soil profile. Although weather conditions can vary quite readily and result potentially in rapidly rising soil temperatures, late February and early March at least are predicted to continue to bring the bitter Arctic/Siberian chill and cold conditions. I don’t care whether it’s called the "Polar Vortex” or the "Siberian Express”, it is simply way too cold for "old man Street." 

This is the time of year when turfgrass managers begin to start thinking about preemergence herbicide applications (March). The good news is with wet soils, snow/ice cover, and frozen soils and most likely the coldest February on record (Ouch!) there is still plenty of time before worrying about the need to apply preemerence herbicides. So, relax, have your plan in place and simply be prepared.

Our best recommendation to be prepared for the proper timing of preemergence herbicide applications for crabgrass control is based on soil temperatures. Why? Because it is an accurate and excellent quantitative measure/guide as to when annual grasses (i.e. crabgrass) will first begin to germinate ( the target window) in the spring.. Crabgrass will typically start to germinate in lawns and landscapes when "nighttime soil temperatures at the 2’ depth reach 50-55 F for several consecutive nights”. So, you can monitor soil temperature daily to see the target window approaching and it can varying significantly from year to year.

So, although there are several methods that can be used to monitor nighttime soil temperatures, the OARDC Weather System website provides daily soil temperatures at the 2” and 4” soil depths every 5 minutes 24/7 (WOW!). It also provides a wide array of other climatological data. You can find this site at the OARDC Weather System website or the OTF website - click on OARDC Weather System on the bottom, click the weather station location closest to you on the map, and then enter the date(s) under the hourly category. We usually use the 2” soil depth temperature at 6AM. Once the nighttime soil temperature at the 2” depth reaches 50-55F for several consecutive nights like a clock crabgrass will start to germinate. 

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