When it comes to keeping weeds at bay in your lawn or garden, using a pre-emergent herbicide is one of the most effective strategies. Pre-emergent herbicides work by creating a chemical barrier near the surface of the soil that prevents weed seeds from germinating and sprouting. Choosing the right pre-emergent herbicide for your needs depends on several factors like the type of weeds you want to prevent, your lawn or garden type, and timing of application.
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How do pre-emergent herbicides work?
Pre-emergent herbicides work by inhibiting weed seeds from germinating. When applied properly before weed seeds germinate, the herbicide forms a barrier near the soil surface that blocks the weed seeds from sprouting. The herbicide does not kill existing weeds, rather it prevents new weeds from emerging. Pre-emergent herbicides are selective, targeting the germination process of weed seeds only. They do not affect mature plants or transplanted seedlings.
Timing of application
For pre-emergent herbicides to be effective, timing the application correctly is crucial. They need to be applied before the targeted weed seeds germinate. This window is typically early spring before soil temperatures reach 55-60°F. For summer and winter weeds, apply pre-emergents 2-4 weeks before their germination period. Proper timing prevents weed seeds from sprouting that season. Pre-emergent herbicides bought in spring will not last all season, so a second application mid-season may be required for full season control.
Common pre-emergent herbicide active ingredients
Some of the most common active ingredients in pre-emergent herbicides include:
- Prodiamine – Controls a wide variety of grassy and broadleaf weeds. Used for lawns, gardens, and under ornamental trees.
- Dithiopyr – Controls crabgrass, annual bluegrass, foxtail. Used for lawns.
- Pendimethalin – Controls annual grasses and certain broadleaf weeds. Used for lawns, driveways.
- Oryzalin – Controls annual grasses and small-seeded broadleaf weeds. Used for flower and vegetable gardens.
- Trifluralin – Controls annual grasses and broadleaf weeds. Used for flower gardens and between patio stones.
These active ingredients vary in their longevity, effectiveness on certain weeds, and approved applications. It’s important to choose a product containing the right active ingredient for your specific needs.
Most effective options for lawns
For homeowners wanting to control weeds in their lawn, below are some of the most effective pre-emergent herbicide options:
Prodiamine
Prodiamine is one of the most popular pre-emergents for lawns. It provides long-lasting control (up to 5 months) against a broad spectrum of weeds including crabgrass, foxtail, spurge, chickweed, oxalis, and more. It is safe for all lawn types. Products containing prodiamine include Barricade, Stonewall, and Scotts Halts.
Dithiopyr
Dithiopyr is very effective against crabgrass and annual bluegrass in cool season grass lawns. It also controls other grassy weeds like foxtail and provides some broadleaf control. Dithiopyr products include Dimension and Hi-Yield Crabgrass Preventer.
Pendimethalin
Pendimethalin provides good control of annual grasses like crabgrass, foxtail, and goosegrass along with some broadleaf weeds. It works well in warm season grass lawns. Pendulum Aquacap and Scotts Halts Crabgrass & Grassy Weed Preventer contain pendimethalin.
Most effective options for gardens
Some top pre-emergent herbicide choices for keeping flower and vegetable gardens weed-free include:
Oryzalin
Oryzalin is a common choice for annual flower and vegetable gardens. It is effective against small seeded weeds like pigweed, lambsquarters, annual bluegrass, and more. Oryzalin products include Surflan and Miracle-Gro Garden Weed Preventer.
Trifluralin
Trifluralin works well in established perennial gardens, shrub beds, and ornamental tree rings. It controls annual grasses and small-seeded broadleaf weeds. Trifluralin can be found in products like Miracle-Gro Garden Weed Preventer and Green Light Rob’s Trifluralin.
Corn gluten meal
For organic gardeners, corn gluten meal is a natural pre-emergent option originating from corn. It provides good control of annual grasses like crabgrass. There are several corn gluten meal products available at garden centers.
How to apply pre-emergent herbicides
Proper application is key to getting the most effective weed control from pre-emergent herbicides:
- Read and follow label directions carefully for timing, rate, and application method.
- Control existing weeds before applying a pre-emergent herbicide.
- Water the area lightly before and after application to move the product into the soil.
- Apply at the right time before target weeds germinate.
- Spread product evenly over the treatment area.
- Wear protective equipment like gloves during handling and application.
Conclusion
Using pre-emergent herbicides is one of the best ways to prevent weed problems in your lawn and garden areas. Products containing prodiamine, dithiopyr, pendimethalin, oryzalin, and trifluralin are very effective options, providing several months of weed control when applied properly. Key tips are to choose a product designed for your specific needs, apply at the right time before weed seeds sprout, and follow all label instructions carefully for success with pre-emergent herbicides.