3/27/2018 - By Harrell's

Spring is right around the corner.......This is a great time of the year as flowers begin blooming, birds are chirping, and the weeds are germinating! We should be thinking about applying preemergence herbicides real soon. As a matter of fact, a great way to determine the best time to apply these preemergence applied herbicides is the use of soil temperature. This is the most accurate means of proper application timing. Over time, many golf course superintendents have learned to coincide some biological occurrence with this timing, such as forsythia blooming or dogwood trees.

I recommend that you go to Wal-Mart or any store that carries cooking thermometers. Buy several of these thermometers and place them around the golf course in various places with different environmental and/or soil conditions. Mark the thermometers with a water permanent ink (Sharpie) at the two inch measurement from the pointed end of the thermometer. Place them in the soil to a depth of two inches (on the mark). For crabgrass, preemergence herbicides should be applied when soil temperatures at a two inch depth are 53 F for two consecutive days. For goosegrass, the timing is when soil temperatures reach 58 F at two inch depth for two consecutive days. Many superintendents will look at applying preemergence herbicides early to make sure they beat weed germination. This works, but the problem is loss of longevity. These herbicides work by producing a herbicide barrier that prevents the weed seed from germinating and becoming established. As this herbicide barrier becomes diluted over time, weed control becomes less effective. The longevity of control is based on herbicide, application rate, and application timing relative to weed germination. With a little bit of effort and data collection, a golf course superintendent can take all of the guessing out of preemergence weed control.