Pre-emergent herbicides are the work horse of any weed control program. A proactive element, pre-emergent herbicides typically contain chemicals that create a protective barrier in the soil which says in place for an extended period of time depending on the use rate. The key player here is usually a compound like prodiamine or dithiopyr or simazine. When applied to the lawn, these chemicals form a shield that inhibits the germination of weed seeds.
Now, weeds are pretty clever. They wait for the right conditions—specifically, the right soil temperature—to sprout. Once the conditions are right for seed germination, the pre-emergent steps in like a bouncer at a club, denying entry to these weed seeds. It disrupts the cell division process in the germinating weeds, essentially putting a halt to their growth which leads to death.
Timing is crucial because you want to get the pre-emergent down before the weeds start their germination dance. You'll want to apply pre-emergent herbicides in early spring before the soil temperature hits the optimal range for weed seeds to sprout. That's usually when forsythia bushes start blooming
So, keep an eye out for those yellow blooms, and that's your cue to lay down the pre-emergent. Once it's applied, water it in to activate the herbicide and ensure it forms that protective barrier. Keep in mind that a pre-emergent herbicide, by definition, won't affect existing weeds; they're more of a preventive measure. So, nipping those weed problems in the bud, quite literally!
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