Oryzalin – This chemical is used in Surflan and several other brands as a broadleaf weed killer also effective against spurge. In turfgrass, it gained popularity for pre-emergent weed control on established, warm-season turf (including Bahiagrass, Bermudagrass, buffalograss, centipedegrass, St. Augustine grass).
All summer you’ve stared angrily at those patches of crabgrass. And you’re still not over this spring, when so many dandelions sprouted that every time the wind blew it looked like snow.
Exactly when your soil turns that temperature will depend on your local climate, and what the weather is like this season. Mid-winter? Early spring? Late spring? Maybe, maybe and maybe.
Could It Damage Your Lawn?
Other popular pre-emergent chemicals include:
Prodiamine – The active ingredient found in the popular Barricade brand pre-emergence herbicide, which tackles about 30 different broadleaf and grassy weeds, including the dreaded crabgrass and annual bluegrass (poa annua).
Don’t expect a miracle. You will not kill all your weeds. The herbicide will not reach all the seeds buried in the soil and weed seeds can sit dormant for years before sprouting. Others will arrive by air in your lawn, sprouted from weeds from your neighbor’s yard or a random patch of weeds miles upwind.
Most of the herbicides you’ll find at the garden center are going to be selective, Grubbs-Bowling says, but choose carefully.
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One other less scientific way to tell when it’s pre-emergent season is to look for early indicating flowers like forsythia. They’re one of the first species to bloom in the spring; typically right around the time soil is reaching the optimum temperature range.
Timing is everything, especially when it comes to the application of pre-emergent herbicides like LESCO’s Stonewall to control summer annual weeds. The general guide is to get the application down before the top 2″ of soil are 50-55 degrees Fahrenheit for five or more consecutive days.
This factor is very important because 20% of the weed seed will start germinating at that time. The other 80% of weed seed germination, especially crabgrass, goose grass and foxtail happens when the soil temperatures reach a consistent 60-70 degrees Fahrenheit. By applying the product just before the soil is a consistent 50-55 degrees, you’re giving it enough time to become activated by water, soak into the soil, and create the chemical shield between the seed and the soil before germination.
1: Map it Out
In addition to proper timing, there are a few other guidelines to maximize pre-emergent results:
Not sure when the soil reaches 50-55 degrees? Start with the USDA’s CRN/SCAN Soil Map to see when the ground typically reaches this temperature in your area. This map is fed by a collection of climate monitoring stations across the country, so you can estimate timing for projects nationally, if needed. Once you have an idea of when this occurs, check the project site using a probe thermometer in the days leading up to this window. Rain and sun exposure can influence the soil temperature and impact your timeline.
Visit your local SiteOne branch and speak with an associate to determine what timing and pre-emergent product will work best for your project. You can also ask an associate for SiteOne’s LESCO® product calendars for general timing and product guidance in your region.