If applied at the right time, a good pre-emergent will form a barrier that keeps your lawn weed-free for months. If the timing of pre-emergent application is wrong, however, all the money and effort spent spreading the product will be for nothing.
If you apply pre-emergent too early or too late, new weeds will come roaring to life. Timing and applying pre-emergent weed killer application is critical to success and keeping a healthy lawn. Pre-emergent or pre-emergence weed killer is one of the most misunderstood weed control methods.
Here are the things you need to know before you get started using pre-emergents for weed control:. The best month for applying pre-emergent weed killer varies by region. In northern areas of the US and throughout most of Canada, temperatures may not be ideal for spring pre-emergent application until as late as May. Warm coastal regions in Florida and California may require spring pre-emergent weed killer as early as January.
For your pre-emergent herbicide to be most effective, time your application based on soil temperature, not the date on the calendar. This will ensure you stop weeds before they sprout. Spring pre-emergent weed killers are designed to stop invasive grasses, such as crabgrass and foxtail, as well as spring weeds like dandelions.
Check soil temperature by viewing a local soil temperature map online or through the use of a soil thermometer. The reason temperature is so important is because warming soil triggers weed seeds to germinate.
By applying pre-emergent once soils consistently reach this temperature, you will stop the widest range of weeds. If you live in the warm southern states, or along the west coast, fall and winter are aggressive growing seasons for winter weeds like annual bluegrass and deadnettle. This will keep those winter weeds from sprouting.
If pre-emergent herbicide is applied too early, it may have reduced effectiveness or no effect at all. Various pre-emergent products are available for lawns, vegetable gardens, and flower beds. Ahead, learn when to use pre-emergent and when not to. Applying a pre-emergent herbicide will prevent seeds from sprouting, but the most effective times to use it are in the spring and again in the fall. Rather than setting a specific date for applying a pre-emergent, a good rule of thumb is to use pre-emergent when spring soil temperatures are around 55 degrees for at least 48 hours.
In southern USDA growing zones , such as Louisiana, this means around the first of March, while the temps will be more conducive to applying a pre-emergent in North Dakota when June arrives. This usually corresponds with daytime temperatures that range from the mids to the mids, indicating the soil is cooling to the temps at which cold weather seeds prepare to sprout. Both types of pre-emergent herbicides, liquid and granular, work in the same way to keep weed seeds from sprouting, and choosing one is often more about personal preference.
A typical step in keeping a lawn lush involves reseeding in late spring or early summer to add more grass to the turf and create a denser yard. A pre-emergent chemical solution may contain one or more of the following active ingredients: Benfluralin - a dinitroaniline herbicide developed to inhibit root and shoot development to prevent weed growth in lawns, crops, and ornamentals. Dithiopyr - a mitotic herbicide developed to inhibit weed root growth in lawns, vines, and ornamentals.
Isoxaben - a benzamide and isoxazole herbicide developed to control broadleaf weeds in vineyards and nut tree orchards. Oxadiazon - a dinitroaniline herbicide developed to control the growth of broadleaves, grasses, sedge, bush vines, and bramble. Pendimethalin - a dinitroaniline herbicide developed to inhibit cell-division and cell elongation to destroy or prevent weed growth in crops, lawns, and ornamentals.
Prodiamine - a dinitroaniline herbicide developed to control weeds in crops such as soybeans, alfalfa, cotton, and ornamentals. Siduron - a dinitroaniline herbicide developed to prevent weeds when seeding or overseeding a lawn.
Trifluralin - a dinitroaniline herbicide developed to control a variety of annual grass and broadleaf weeds in tree fruit, nut, vegetable, and grain crops. How Does Pre-Emergent Work? Depending on the formula used, pre-emergent works in one or more of three ways: Inhibits plant root growth Inhibits seed cell division Inhibits specific enzymes essential to the growth of certain plants As you can see from the previous list, most pre-emergents have dinitroaniline herbicides.
Does pre-emergent kill weeds? Does pre-emergent kill crabgrass? Last year, did you have enough space on your property to store plowed snow? Get a Quote. Ensure you remain compliant with the law by reading up on the local rules below. Eddy Zakes. November 10,
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