Lawn weed control is among the most tedious elements of a lawn care regimen. What products to use, the timing of their application, and their relative safety are just a few of the questions a lawn owner needs answered in order to begin a weed control program.
Weeds can be controlled with chemical herbicides or through organic methods.
Chemical Weed Control
Chemical weed killers, when used properly, can be an effective component of an Integrated Pest Management program. Weed control with herbicides should be part of a larger lawn care program designed to encourage turf health and vigor, and keep weeds to a minimum.
Herbicides can act upon a weed in two different ways.
- Pre-emergent herbicides act upon weed seeds, seedlings or form a barrier in the soil to prevent weed seed germination or establishment. Pre-emergents are usually used in the spring to prevent crabgrass seeds from establishing when the soil temperatures begin to warm up. A properly timed application can provide control for several months. Products like Dimension (ai-dithiopyr) and Pre-M (ai-pendimethalin) work at suppressing all seeds in the soil, so any re-seeding projects are out of the question for a few weeks. Tupersan (ai-siduron) is notable as the only pre-emergent herbicide with the ability to suppress crabgrass and be used in conjunction with grass seed.
Post-emergent herbicides work on actively growing weeds and can be further broken down into selective or non-selective categories.
- Selective herbicides can be applied to a lawn and target weeds while having little effect on grass. Products containing the active ingredient 2,4-D, dicamba, and MCPP are commonly used to control a wide variety of broadleaf weeds. Grassy weeds and grass-like weeds can be harder to selectively target with herbicides. Products containing the fenoxyrop ethyl, dithiopyr, or quinclorac can be used for post-emergent crabgrass control. Some products may require repeated applications for effective control. Nutsedge is a particularly stubborn weed to eradicate in the lawn, the relatively new product Sedge Hammer (ai-halosulfuron), formerly known as Manage, is the only herbicide to successfully target both yellow and purple nutsedge.
Non-selective herbicides kill everything they come in contact with, including lawn. Extra care must always be taken when handling non-selective herbicides to prevent spillage or accidents. The most popular non-selective herbicide is probably Round-Up (ai-glyphosate). Its new formulation Quick Pro adds the active ingredient diquat dibromide for fast acting results within 24 hours. Non-selective herbicides tend to be used very sparingly in a lawn unless applied meticulously to individual weeds or wiping out an entire lawn due to be renovated.
How Are Herbicides Applied?
Herbicides are commonly applied in granular and liquid form. Granular herbicides are easily applied with a common push-type spreader and can come blended with a fertilizer. The downside of granular applications is that they must be broadcast over a large area, applying chemical in places that may not need it. Pre-emergent crabgrass control and "weed and feed" products are common granular forms of herbicide. Liquid herbicides are diluted with water and sprayed onto the plant with a hand-held or backpack sprayer. Spot spraying broadleaf weeds, like dandelions or clover with a selective post-emergent herbicide is effective and saves the lawn from excessive chemicals
Organic weed control is much more than killing weeds safely. It is first about growing healthy turf in fertile soil and minimizing weed pressure. Organic weed control is further achieved by using an Integrated Pest Management (IPM) program to establish weed thresholds, prevent weeds, and eradicate as a last resort.
There is no quick fix, magic spray weed killer in organic lawn care. Organic weed control is more about the holistic organic management of the lawn and soil, which results in fewer weeds. The theory (and practice) being that a healthy lawn and soil will promote turf growth which will out-compete weeds.
Correct cultural practices must be performed to reduce the opportunity for weeds to thrive. Weeds thrive on weak, stressed turf and compacted, unhealthy soil. Eliminate those conditions and grass will win over weeds.
- Mow at the highest level possible to encourage a dense lush, lawn capable crowding out of weeds.
- Reduce compaction by aerating.
- Improve water and nutrient uptake by de-thatching,
- Topdress with compost.
- Re-seed bare patches in the fall to avoid them from being taken over by weeds in the spring.
- Avoid scalping the lawn when mowing. Damaged crowns recover very slow and give weeds an opportunity to establish.
- Water deeply and infrequently, maintain adequate soil moisture but do not over-water.
If the need for eradicating weeds is still present, a multitude of organic methods are available.
- Corn gluten meal is an organic pre-emergent herbicide with fertilizer. Like it's chemical counterpart, it suppresses seed germination and provides a quick green up.
- Acetic acid in vinegar has plant killing properties and can be used as a non-selective weed killer. Household vinegar does not get above 5% acetic acid and weeds would need repeated applications. Stronger concentrations are available as weed killers. Remember, non-selective means it kills all plants, so handle with care.
- Herbicidal soaps are natural products for controlling mosses and algae and there are numerous weed killing formulations using natural oils, concentrates and other organic substances. They are all non-selective herbicides and as of yet, there are no organic broadleaf (selective) herbicides available.
- Mechanically remove weeds with manufactured weed puller tools, long screwdrivers, hand trowels, or bare hands.
- Weed flamers are gaining popularity as an organic weed control. They are basically modified propane torches used to burn problem weeds.