Early spring is the time of year to prevent crabgrass in your lawn. I just spread Scotts Turf Builder with Halts crabgrass preventer on the lawn. A few years ago I tried going the organic route and used a corn gluten product that was supposed to stop crabgrass. It smelled nice, like masa harina, the corn flour used in making corn tortillas! The problem was it didn’t work very well for me.
So I’m back to Scotts. The product that I put on the lawn has a high nitrogen fertilizer in it that will help the grass green up quickly. It also has a crabgrass preventer that Scotts calls Halts. I did some checking to find out what Halts is – it’s the chemical dithiopyr.
In the world of herbicides, there are preemergent and postemergent herbicides. Preemergent herbicides prevent weed seeds from germinating and/or developing normally. Postemergent herbicides affect weeds that are already growing.
Dithiopyr is a preemergent herbicide – it doesn’t kill crabgrass that is already growing. Instead it prevents the crabgrass seeds from growing into crabgrass plants. It’s put on the lawn in early spring when the forsythia bushes are blossoming. This is the time to apply dithiopyr because crabgrass seeds haven’t started to germinate but they will begin to grow within the next 2-3 weeks as the soil warms.
I’m fascinated by the way this chemical works. Dithiopyr is a mitotic inhibitor of normal cell division in the germinating crabgrass seed. If you remember back to biology class, mitosis is the process by which cells multiply. During seed germination, mitosis is happening at a rapid rate. Dithiopyr affects mitosis in germinating crabgrass seeds by inhibiting the formation of the microtubules which are necessary for the chromosomes to separate correctly during cell division. When dithiopyr is present, the germinating crabgrass seeds are unable to grow into healthy plants because its cells can’t divide normally. And that means no crabgrass!
But whether you care about how this herbicide works or not, the important thing is that it works. If you want to have a crabgrass-free lawn, a preemergent herbicide is the way to go.