Weed control in Lawns

In this guideline, we will study:

• Weed identification
• Weed invasion
• Weed management before planting
• Weed management in newly planted lawns
• Weed management in established lawns
• Renovating lawns

Weed control in Lawns

Every lawn has weeds, but in well-maintaining and actively developing turfgrass, they rarely cause issues. Giving a new lawn a good start depends on proper site preparation and grass selection before planting. Once the grass has been established, poor management habits that weaken it—such as inappropriate watering, fertilizer, or mowing—are the key causes probably likely to predispose it to weed invasion. Activities that lead to compaction also add considerably to turfgrass stress, making it more straightforward for weeds to invade.

An integrated weed control approach may decrease most weed populations to bearable levels and prevent big, ugly weed patches. For most lawns and park grass, total eradication of weeds is not a reasonable or required aim; rather, with good management, a lawn may be essentially free of weeds without using pesticides extensively.

Weed Identification

Management depends on identifying weeds and understanding their life cycles. Lawns abound with three main types of weeds: broadleaves, grasses, and sedges. Make sure you separate similar-looking lawn grasses from weedy grasses.

Weeds can have an annual, biennial, or perennial life cycle. Commonly found as either winter (cool-season) or summer (warm-season) annuals, annual weeds survive just one season. They should not be under control before flowering; they can generate seeds that sprout during the same growing season or the following year. Cool-season annuals may grow in summer (or year-round) in mild regions or lawns impacted by microclimates; warm-season annuals may grow in winter (or year-round).

Though seed is not produced until the second year, biennial weeds survive either vegetatively or by seed for two growing seasons. Though they release seeds, many perennial weeds reproduce vegetatively via creeping stems (stolons and rhizomes), tubers, or fleshy roots over many years. Once established, perennial weeds are often the toughest to manage.

Weed Invasion

Weeds are common invaders of turfgrass over- or under-watered, inadequately fertilized, badly mowed, or firmly compacted. Because there is more open space for a weed to spread, lawns damaged by plant diseases or insect pests grow weedy. Most weed invasions can be avoided with appropriate lawn care and sound preventative measures or corrected with overseeding. Finding the species of weeds present can help indicate the invasion’s underlying cause and guide actions to lower the weed count.

Weed Management Before Planting

A beautiful, healthy lawn starts with adequate preparation. Clear any current vegetation before planting so that your grass has the best opportunity to grow. If you have annual weeds, irrigate the area to encourage their sprouting, then either shallow cultivation or a nonselective herbicide like glyphosate or clove oil should assist you in eliminating them. If you are planting with seed or sod, especially, keep the process going until the area is totally weed-free.

Given they return year after year, perennial weeds are more difficult to eradicate. Digging as many as feasible and then tending the ground can help to bring any buried roots, branches, or tubers to the surface. Warm, dry conditions assist in their drying out process, therefore facilitating their removal. If your weed problem is severe, you might have to stop watering and continue working the ground for several months to bring up and eradicate any last propagules. Some weeds, such as purple nutsedge and field bindweed, are quite tenacious, though, and may call for several treatments using a systemic herbicide such as glyphosate.

Soil solarization can be a good method to manage weeds if you want a chemical-free approach before planting. After tilling and preparing the area, cover the moist soil with clear plastic sheeting (1 to 2 mils thick) and fasten the edges with dirt. In inland California, where high temperatures help kill weed seeds and roots, this approach performs best in the peak summer months—June through August. For optimal effects, keep the plastic in place for four to six weeks. Solarization may not work on stronger weeds like bindweed or nutsedge, though, and it is less successful in colder coastal locations or under shade.

Beyond simply weed management, the growth of your grass depends much on the condition of your soil. While sandy soils may benefit from additions to better retain moisture, many soils require some assistance; clay-heavy soils gain from amendments to promote drainage. Good drainage ensures that roots get adequate air, water, and nutrients, which are all necessary for healthy grass. If you are importing topsoil, be sure it comes from a reputable source devoid of pesticide residue, pebbles, and weed seeds. Right preparation can help you build the ideal basis for a long-lasting, rich, green grass.

Table 1. Special Weed Problems in Lawns and their Associated Conditions.

Select an Appropriate Turfgrass Species

Different kinds of turfgrass have different tolerances to severe temperatures, shade, drought, and wear. Their temperature preference and times of active development guide their two main classifications: cool-season and warm-season grasses.

Cool-season plants such as Kentucky bluegrass, perennial ryegrass, and tall fescue flourish around 60–80°F and may go into a semi-dormant state in hot or icy conditions.

Generally, cool-season grasses call about 25% more water than warm-season grasses cultivated in the same area and are less drought-tolerant. Select a species for your particular situation while laying a lawn. Poorly suited species demand more extensive care than well-adapted plants and are more vulnerable to weed incursions.

Selecting a planting date will help the turfgrass species compete with weeds and establish rapidly—plant warm-season grass from mid-spring through July. Early spring or fall is the time to grow cool-season grasses. The quick establishment of lawns will help them fight weeds more successfully. From the minute they are laid, sod-based lawns show few weed issues. Lawns grown from plugs, solons, or seeds might take up to two months to develop and are thus more vulnerable to weed incursions.

Weed Management in Newly Planted Lawns

Even with meticulous preparation of a planting location, some weeds will most likely grow in a new grass. As weeds show up, manually remove them. This will stop them from launching the invasion and creating seeds. Fertilization, mowing, and well-timed watering help manage weeds. The first several weeks following turfgrass root establishment are short, just reaching the top few inches of soil. Water is enough to keep the root zone wet without flooding the ground. Once the grass is established, use deep, infrequent watering to promote good root development into more profound depths. When the roots of young lawns are fully anchored in the ground, mow them for the first time. Ensure the ground is relatively dry to prevent the new turfgrass from being ripped from underneath.

Weed Management in Established Lawns

Irrigation

Many lawns are irrigated incorrectly. Bad watering techniques may damage grass, allowing weeds to creep in. Annual bluegrass, crabgrass, dallisgrass, and nutsedge flourish in under-irrigated lawns. Good grass requires consistent water coverage. Broken, blocked, or set too low or too high sprinkler heads may not cover all of the lawn and cause dry or dead patches in otherwise healthy turfgrass.

Generally speaking, deep, infrequent watering promotes strong root development. Only after the grass has recently been planted and the root system is growing should light, regular watering be necessary. Light and frequent watering of established grass produce a shallow-rooted lawn that is less resilient and lets shallow-rooted weeds like crabgrass have a competitive advantage. Grass should be watered sufficiently deep to reach the soil’s six to eight-inch depth. Between waterings, let the ground gradually dry out. Before water is once more sprayed, the top one to two inches of soil should be somewhat dry.

Different turfgrass species have different water needs; however, growth circumstances, climate, and time of year affect these needs. Generally speaking, warm-season grasses require watering once or twice a week. In warmer weather, cool-season grasses need irrigation more frequent irrigation up to frequently. Growing in shadow, turfgrass species call for less water than those growing in full sun.

Because clay soils hold water longer than sandy soils and because sandy soils drain water and dry up rapidly, turfgrass growing on clay soils does not require as regular watering as turfgrass grown on sandy soils. Sometimes, modest application rates and/or partition of total irrigation time into two or more applications per day are necessary on clay soils to facilitate water penetration and minimize puddling and runoff.

Mowing

Every type of grass has particular mowing height needs. Cutting some grasses too short could damage the turfgrass and encourage weed invasion. On the other hand, if some grasses are not cut short enough, the thatch layer might grow and reduce water penetration, compromising the turfgrass.

Mow grasses more often while they are actively developing. A conventional suggestion is to remove no more than one-third of the leaf blades at every mowing. If too much is removed at once, the grass may not recover for some time, allowing weeds an opportunity to spread.

Lawns afflicted with weed infestations can seem uneven. Frequent mowing of weedy lawns helps to avoid their patchwork look and stop the development of flowers and weeds. Make sure the mower blades are sharp enough not to harm the grass. To prevent the spread of weeds, cut the least weedy region first and the weediest section last for significant areas.

Afterwards, washing the mower’s underside and deck will eliminate weed seeds. The same holds true if mowers are taken from weedy lawns to other lawns to prevent spreading weed seeds and propagules. Steer clear of cutting grass when wet, like following irrigation or rain; running a mower over moist ground can cause compaction.

Fertilizing

If you want a good lawn, strictly follow fertilizer recommendations. Start a regular fertilizing schedule about six weeks after planting. Lawns should generally be fertilized four times a year while actively developing, using no more than one pound of real nitrogen per 1,000 square feet per treatment.

Thatch

Regular thatch removal will assist in maintaining your turfgrass’s health and competitiveness with weeds. Between the turfgrass blades and the ground surface lies a layer of organic stuff called thatch—stems, stolons, roots. Regular and even helpful is a little covering of thatch; it helps control weed germination.

Certain grass species, especially warm-season creeping grasses, create thick thatch layers that can stop nutrients, water, and air from moving through the ground. Usually, you should dethatch your grass when the thatch layer thickness exceeds one-half inch. Some species, such as Kentucky bluegrass, bermudagrass, or zoysiagrass, might involve dethatching annually. For some species, including tall fescue, dethatching could be either necessary every five years or not at all. On tiny lawns, gently remove the coating of thatch with a thatching rake; on creeping-type grass lawns, such as bermudagrass, cut across the lawn to the soil surface with a verticutter or dethatcher.

Aeration

Intense traffic over time can firmly compact dirt. Limiting the oxygen, water, and nutrients accessing the roots helps slow turfgrass development and raises its susceptibility to weed invasion. Regular aeration will help to lower soil compaction. Lawns with deep clay soils or heavy foot or equipment traffic may need aeration several times a year, while lawns with little activity may need to be aerated once a year or less.

Sometimes called aerators, aerators cut small soil cores or generate channels or pores in the rooting zone. On small grassy areas, a hand-held aerifier could be plenty. More significant regions gain from machine-driven verifiers, which equipment leasing firms provide. Aerate when the grass is in vigorous growth. While some weed seeds could flourish in the area then, aeration will create temporary holes in the grass that will gradually fill in a few weeks. Usually left on the grass surface, soil cores break down quickly under watering; some may carry weed seeds. On lawns known to be weedy, following aeration should be considered applying a preemergence insecticide.

Hand weeding

Manual plucking may be all you need to control sporadic weeds if you follow correct and frequent management practices. Preventing infestations of creeping woodsorrel (oxalis), nutsedge, dandelion, spurge, dallisgrass, and Bermudagrass calls especially for hand weeding.

Remove weeds when they are still young and before they set seed or form rhizomes or tubers. Eliminate small areas before they grow in scope. Regularly doing this will help your grass be weed-free. Take out the whole weed, including the root. Eliminating weeds with a thick taproot calls for a dandelion fork or fishtail weeder. More significant portions can be excavated, and clean dirt can be filled in the holes.

Herbicides

Generally, herbicides are not required if your grass is in good shape. Use them as part of an integrated management program that includes good cultural maintenance practices when needed. Not all herbicides can be used on all grass species, and no herbicide can eliminate lawn weeds. Before deciding on a herbicide, determine your weed problem or problems and turfgrass species.

Some perennial grasses, among the most severe lawn weeds, cannot be adequately managed with herbicides without harming the turfgrass. The goods listed here are primarily for home lawns.Herbicides are categorized in numerous ways:

• preemergent or postemergent
• contact or systemic
• selective or nonselective.

Before weeds appear from the ground, preemergence herbicides kill weed seedlings as they germinate and attempt to surface. Although preemergence herbicides are useful against numerous broadleaf weeds, they are primarily employed in lawns against annual grass weeds such as annual bluegrass and crabgrass. Following weed emergence from the ground, postemergence herbicides target actively growing weeds. Postemergent herbicides may exhibit either systemic or contact action.

Applied to immature weeds, contact herbicides are most effective; they induce localized damage where the chemical comes into touch with the plant. Among these are diquat, carfentrazone, vegetable oils and herbicidal soaps. In contrast, systemic herbicides migrate into the plant, causing harm in more places and can control older weeds. Examples include glyphosate, quinclorac, triclopyr, 2,4-D, dicamba, and mecoprop mixes (active chemicals in many broadleaf weed killers).

Herbicides can help keep your lawn weed-free, but choosing the right one is essential. Selective herbicides target specific weeds without harming your grass. For example, 2,4-D is excellent for removing broadleaf weeds while leaving grass untouched, whereas fluazifop works the opposite way—it kills grassy weeds without affecting broadleaf plants.

On the other hand, ‘nonselective herbicides’ don’t discriminate—they kill just about anything they touch, including your lawn. These should only be used before planting new grass, during a lawn renovation, or for spot treatments on stubborn weeds. Some standard options include diquat (a contact herbicide), plant-based oils (also contact herbicides), and glyphosate (a systemic herbicide that works throughout the plant).

Table 2. Examples of Herbicides Available for Use in Residential Lawns.*

B. Selective Postemergence Herbicides (Herbicides applied after weeds emerge).

C. Nonselective Herbicides for Use in Turfgrass Renovation
(Will kill existing lawn and plants).

Herbicides for Broadleaf Weeds

On grass lawns, annual broadleaves are the easiest weeds to manage. Many products are on the market and designed for particular weeds or usage on particular turfgrass species. Usually, postemergence, systemic herbicides with combinations of two or three active chemicals, such as dicamba, mecoprop, or 2,4-D, are effective in suppressing many broadleaf weeds without harming grass lawns. Triclopyr is also an effective broadleaf herbicide but will cause injury to bermudagrass lawns and other stoloniferous turfgrass; it is safe to use on most cool-season turfgrasses such as bluegrass, ryegrass, and tall fescue lawns. Often combined with the other broadleaf herbicides to boost the speed or scope of weed control, newer herbicides such as carfentrazone and quinclorac also have broadleaf weed activity.

Broadleaf herbicides and their combinations are also effective against perennial broadleaves. However, more than one application may be necessary. Especially when applications are made in windy conditions, many postemergence broadleaf herbicides are prone to drift in the air and may contact desired plants. Also, be aware that certain postemergence broadleaf herbicides, such as dicamba and triclopyr, can be absorbed by tree roots growing in lawns and may cause tree harm if applied too close to the tree drip line. Always refer to the herbicide label for particular application instructions and safety considerations.

Herbicides for Grass Weeds

Common preemergence herbicides, such as benefit, bensulide, dithiopyr, oryzalin, pendimethalin, and prodiamine, will help adequately control annual grasses, including crabgrass, foxtail, and annual bluegrass, in established lawns. Preemergent herbicides that target a smaller spectrum of weeds in certain turfgrass species are dimethenamid-p, ethofumesate, and indaziflam.

Applying any preemergence herbicide 2 to 3 weeks before weed germination is the secret to their success. Preemergence herbicides are most effective when the ground is moist. Still, the grass is dry at the time of treatment and when carefully irrigated into the lawn immediately following application. It may take three treatments per year (early fall, late winter and mid-spring) to clean up a large weed infestation, but herbicides should not be needed year after year if cultural practices are adapted to favour the turfgrass. After using a preemergence herbicide, be advised that overseeding or reseeding lawns may not be feasible until weeks or months later.

Controlling weedy grasses developing on existing lawns using postemergence herbicides is far more challenging. Though not as efficiently as preemergence herbicides, products containing quinclorac are accessible to homes and help to control crabgrass, foxtails, and barnyard grass infestations; numerous applications are needed in the summer and following years. Though applications are rare in residential lawns and more common in highly managed golf courses and commercial turfgrass, professional applicators may use ethofumesate (a preemergence herbicide with some postemergence activity), foramsulfuron, and sulfosulfuron to remove grass weeds from turfgrass lawns selectively.

Some permanent grasses, such as bermudagrass, dallisgrass, or knotgrass growing on a tall fescue lawn, are tricky to manage. Often, a nonselective systemic herbicide such as glyphosate or the grass-selective systemic herbicide fluazifop is required. Use spot treatments since these herbicides will also harm grass. Applied in early fall, before the weedy grass enters dormancy, they are most effective when weeds actively develop. Regular triclopyr, fenoxaprop, or fluazifop will also help control Bermuda grass development in a tall fescue lawn. See the labels on products for particular instructions.

Herbicides for Broadleaf and Grass Weeds

When using preemergence herbicides, apply them after any aerating and/or dethatching; otherwise, the herbicides will be removed from the soil with the cores or the thatch, and the herbicide activity will be reduced. Some preemergence herbicides for use in lawns will effectively control specific weeds (both grasses and broadleaves), as indicated on their labels.

Herbicides for Sedges

Spot administrations of a nonselective systemic postemergence herbicide like glyphosate can destroy sedges like green killing and yellow and purple nutsedge. Alternatively, two treatments of the selective postemergence herbicides halosulfuron, sulfentrazone, or sulfosulfuron efficiently eliminate sedges from lawns.

Highly prolific and helps this sedge spread its green-killing seed. Most preemergence herbicides stop killing seedling emergence quite well. Yellow and purple nuts are mainly distributed via tubers. No preemergence herbicides damage nutty tubers in cool-season grass. Dimethenamid-p has an action on nudges and green killing in warm-season lawns; metolachlor is registered for control of yellow nutsedge (and its tubers). Both of these items are for professional use only.

Herbicides for Newly Seeded Lawns

Herbicides should be used carefully on freshly planted lawns as they are sensitive. On newly sown or established cool-season turfgrass for control of broadleaf seedlings and warm-season grass weeds like crabgrass, foxtails, and barnyard grass, just mesotrione and siduron among the preemergence herbicides can be employed. Available to home gardeners, mesotrione is combined with planting beginning fertilizer. Only a trained applicator should use siduron; it should not be used on warm-season grass species. Once the turfgrass has generated several tillers and mowed twice or three times, post-emergent herbicides selective for broadleaf weeds can be sprayed once.

Weed and Feed Products

Some fertilizer formulations contain either preemergence or postemergence herbicides (or both) for weed control (typically crabgrass prevention or broadleaf weed control). Use these combination products only when the lawn has a known weed problem and not every time you fertilize. Only apply herbicides when you are convinced treatment is required and have seen significant quantities of weeds. With preemergence products, this means depending on past season weed counts. Be sure the active component in the product will control the weed species causing your difficulties and that the application’s timing is suitable. Applying preemergence herbicides after most of the target weeds have sprouted is pointless.

Other Weed Control Products

Maize gluten meal is a fine yellow powder that is a waste product from the processing of maize. It is typically sold for weed control. It may be top-dressed onto existing grass and has significant nitrogen content. Although studies done in the Midwest point to repeated applications of corn gluten meal possibly preventing some weed emergence, the data are inconsistent.

On California lawns, maize gluten meal was insufficient for weed control in tests. However, maize gluten meal may aid in weed management since its high nitrogen concentration functions as a fertilizer, making turfgrass more competitive with weeds. Additionally, it may function as a mulch to reduce weed germination. Together, these elements help corn gluten meal succeed at a low density of annual weeds on thick grass. Meal composed of corn gluten has little effect on already existing weeds.

Herbicide Success Tips

Garden and lawn firms promote their brand names of herbicides. These trade names are so numerous and change regularly that they cannot all be mentioned in this article. Look for the common term or active ingredient listed on the label in the tiny type under “Ingredients” to guide your herbicide shopping. Unlike brand names, common names for active substances don’t vary from business to company. Different products will differ in the percentages of active substances they contain. Many products are made as higher-concentration liquid sprays that need mixing with water; others are designed as ready-to-use, allowing for the ease of no mixing; others are granules.

Use herbicides at the specified rates and at the appropriate time of year, following all package guidelines attentively. Be sure the herbicide is efficient against the weed you are attempting to control and that it is suggested for your kind of grass. Inappropriate application could damage or kill intended landscaping plants, including valuable grass.

Remember that many broadleaf weed herbicides can harm shallow tree roots developing in the grass or cause drift; hence, use great care. Avoid using herbicides under hot, dry, or windy circumstances, as they might damage surrounding ornamentals or grass.

Remember that you cannot reseed desired turfgrass species for several weeks or months following application when you are using preemergence herbicides. Apply preemergence herbicides after any aerating or dethatching; otherwise, the herbicides will be removed from the soil with the cores or thatch, disrupting the uniform herbicide barrier on the soil surface.

Renovating Lawns

Find out why your lawn grew weedy before you renovate it. Was the appropriate grass species you were cultivating for your location? Did you apply the suggested mowing, fertilizing, and watering techniques? Did your drainage work well? Correct the issues that let weeds overrun your lawn in past years before you replant. Apply sound lawn care techniques to help to lower new weed incursions.

If weeds have taken over a tiny portion of your lawn, you could consider a partial overhaul. Clear the impacted area, pull and eliminate weeds, then use a garden rake to work the soil, breaking up clods and clearing weed waste. After adding starting fertilizer and soil additives, level and harden the ground. Irrigate once again once sod, seed, stolons, or plugs patch the ground.

If your lawn consists mainly of weeds, a complete makeover might be required. Killing and removing the current grass and weeds comes first in a whole overhaul. One can eliminate a lawn in several ways. You may remove the weeds and grass, prepare the ground for planting, and then solarize the ground. You might also rototill the old grass and gather the weeds and old turfgrass. Until the trash is all gone, you will have to keep tilling and raking.

Another approach is to kill the current grass and weeds with a nonselective pesticide like glyphosate, clear all the plant material you can, and till the soil until the trash is gone. After removing the old grass, prepare the place as advised above and plant the new lawn.