#625 Weed Identification and Control
A weed is any plant or grass growing where you don’t want it. We have lawn weeds for reasons like mowing too close or scalping, too little or too much fertilizer, too much shade or foot traffic, and insect or disease damage. Prevention of these problems is the best control. Other controls range from pulling by hand to using a wide variety of herbicides. Most lawn weeds can be prevented with a strong maintenance program that follows proper water and fertilizer practices. In flower and shrub beds, a 2-inch layer of mulch will help keep weeds at bay. If using herbicides, follow package instructions!
DIFFERENT GROUPS OF HERBICIDES
POST EMERGENT HERBICIDES
For weed killers, there are two basic groups of post emergent herbicides, selectiveand nonselective. Selective products kill weeds listed on the label but should not be used inside the drip line of desirable plants. Nonselective products kill weeds and plants listed on the label but may severely injure or kill nearly all other plants as well. Nonselective, foliar (applied by wetting the leaves) products are safe to use on weeds in tree wells and around ornamental shrubs as long as you don’t get solutions on leaves of the ornamentals. The most often used nonselective herbicides are Remuda® and Round-up®. These glyphosate based products will not move through the soil. Areas where it is applied can generally be replanted within a few days after use. As always, follow label instructions exactly when applying any herbicide. Don’t apply on a windy day or drift may cause injury of desirable plants.
PRE EMERGENT HERBICIDES
Understanding the difference in pre-emergent and post-emergent herbicides is important. Pre-emergents prevent weeds by stopping seeds from germinating but will not harm established plants. They’re most effective when applied before weeds begin showing up. Post-emergents emergents kill established weeds but don’t prevent new ones from sprouting.
Bermuda grass is a common turf grass that becomes a nuisance weed by spreading where it isn’t wanted. A vigorous perennial that thrives in our climate, it’s often mistakenly called crabgrass which is a different kind of weed altogether. Bermuda grass spreads underground by rhizomes and on the surface by fine, easily transported seed. It has a very fine, pointed leaf and spreads rapidly by use of runners.
Controls: Hand weeding is not very effective because the smallest stem or root piece will start a new crop. Glyphosate products like Remuda® or Round-up® are highly effective when applied to leaves of actively growing bermuda. Several applications may be needed for complete control. If runners are present in desirable turf, wipe them with a cotton rag soaked in the herbicide or place them on cardboard before spraying. This will avoid any residual turf damage caused by spraying. Use of herbicides while bermuda is dormant (brown) will have no effect.
Crabgrass is a summer annual that spreads rapidly through seed dispersal. A clumping, broad leafed, hairy, shallow rooted plant, it will thrive in a thin, under-fed, over watered lawn and will eventually take over if left unchecked.
Controls: Good cultural practices and regular fertilization keep a thick, healthy turf which prevents crabgrass from gaining a foothold in your lawn. Apply a pre-emergent in February to prevent seed germination. If the weed appears, spot treat with a commercial crabgrass killer and dig out any large clumps. Broadleaf weed killers have no effect on crabgrass.
Dallis Grass is a perennial that thrives in summer. Large flat stalks grow from a central crown-shaped ring 4-8 inches across. It spreads through rhizomes and seeds and can be difficult to spot in fescue lawns. It rapidly outpaces normal growth of fescue and shows itself for eradication.
Controls: Pre-emergents are not effective. Spot spray with a commercial crabgrass or grassy weed killer. Watch over spray in hot weather as it may damage other turf grass.
Bur Clover is a low-growing, trailing, densely matted, annual weed that reproduces by seed. Its clover-like leaves and yellow blooms will begin to dominate any poorly maintained lawn in early summer. If not controlled, it can crowd out lawn grasses.
Controls: Follow good maintenance and fertilizing practices to keep a strong, thick turf. Spot spray with a commercial, selective product like Bayer All-In-One Weed Killer or Ortho® Weed-B-Gon® to eradicate. Watch over spray in hot weather and wind drift around ornamentals.
Dandelion is a broadleaf perennial with prolific yellow flowers and jagged green leaves. It spreads by seeds and sprouting crowns from the roots. A single taproot will re-grow if broken off at or below ground level. Seed can germinate year-round.
Controls: A thick, healthy turf will restrict this pest. Apply a pre-emergent in early spring and use a selective broadleaf weed killer like Bayer All-In-One for individual plants. Watch over spray in hot weather.
Mallow is an annual that reproduces through seeds. It has large, fan-shaped leaves at the top of a long stalk and flourishes from early spring through fall. Mallow is usually found in thin, poorly maintained lawns.
Controls: Keep a thick, healthy turf. Use a pre-emergent in early spring to stifle seeds. Spot treat individual plants with a broadleaf weed killer.
Oxalis is an aggressive, clover-like perennial which develops a vigorous, spreading root system. Small, yellow flowers form seed pods that can shoot seed up to 6 feet when ripe. This weed can take over if not controlled.
Controls: Apply a pre-emergent in early spring. Spot treat existing plants with a broadleaf weed killer or pull them by hand. Watch over spray in hot weather and drift on windy days.
Purslane is a succulent, low-growing annual that reproduces by seeds. It thrives in hot, dry summers and shows up later than most weeds in bare spots, flower and shrub beds and thin lawn areas.
Controls: A late spring application of pre-emergent herbicides will control infestations. Pull the shallow rooted plants whenever you see them.
Spurge is a low-growing, spreading annual that can live through a mild winter. It forms dense mats of mouse-eared leaves over a central taproot and spreads through heavy seed production. This one is especially noticeable along the edges of lawns, driveways and sidewalks. It also thrives in bare spots and thin turf areas.
Controls: Prevention is the best cure. Keep your lawn thick and healthy. Apply a pre-emergent along lawn edges and pull whenever it appears in walk and driveway creases. Pull large plants carefully so you Don’t break the taproot and spot spray small plants with a commercial broadleaf weed killer product.
Lawn Weed Identification: Common Lawn Weeds
Weeds are a common occurrence in most lawns and gardens. While many of them are quite familiar, there may be some that are not. Learning about some of the most common types of weeds can make it easier to eliminate them from the landscape.
How to Identify Weed Types
In order to identify weed types and bring them under control, it’s important to understand how they grow. Like other plants, weeds can be annual or perennial. Annual weeds are less troublesome as far as control measures go. While they are known to sprout up nearly anywhere due to seed dispersal, their root systems are relatively shallow. This makes them easy to pull and eradicate, although doing so before they set seed is recommended.
Common annual weeds include:
Perennial weeds, on the other hand, have more extensive root systems, including taproots, making them more difficult to control. In addition, these weeds come back each year, especially if the roots are not destroyed. Some of the most common (and problematic) perennial weed types include:
Lawn Weed Identification
One of the best ways to identify lawn weeds is by looking closely at the soil in your landscape. Many common lawn weeds can be found growing in certain types of soil, making this an excellent way to identify specific types you may have growing in your landscape. Here are some of the most commonly seen weeds:
Dandelions: Dandelions are well known in many lawns and gardens– their fuzzy yellow blooms popping up nearly anywhere. While their deep taproots make them difficult to control, they generally spread through their easily recognized white, fluffy seedheads.
Ragweed: Ragweed is commonly known by many allergy sufferers. This annual weed can be seen most often during summer (and autumn) months and recognized by its fern-like foliage.
Crabgrass: Crabgrass is a homeowner’s worst nightmare, creeping up throughout the lawn. This summer annual lies flat to the ground and has reddish purple stems (both smooth and hairy). It forms slender spike-shaped seedheads just below mowing height, making it difficult to manage.
Spotted spurge: Spotted spurge has a reddish purple spot in the center of each leaf and the sap is milky (which may cause a rash in sensitive individuals). This annual weed can be pulled up easily in moist soil. Improving the density of lawn grass can help keep it under control.
Common chickweed: Common chickweed is a mat-forming weed with tiny, star-shaped white flowers. This annual thrives when conditions are cool and moist. Mouse-ear chickweed is similar, however, this weed is perennial with hairy stems and leaves, and is more tolerant of summer heat.
White clover: White clover is a perennial weed that forms creeping runners and produces white, fluffy-looking blooms. Since this weed is a legume which fixes nitrogen, it is often found in lawns with low fertility. Adding nitrogen to the soil can help ease the population of clover.
Common nettle: This is prolific in soil that borders gardens and open fields. This perennial weed has many varieties, including stinging nettle. While it may look like an ordinary, hairy weed with attractive little flowers, it can cause a very painful sting if you touch it. Nettles can often be aggressive spreaders, with creeping roots.
Broadleaf plantain: Broadleaf plantain is a low-growing perennial. It has broad leaves with prominent veins and may smother lawn grass if left untreated, which generally calls for maintaining thick lawn coverage.
Knotweed: Knotweed is an annual weed, common along sidewalks. It usually thrives in dry, compacted soils. Knotweed forms a tough, wiry mat of stems and blue-green leaves with small white flowers. It is often confused with spurge, however, this weed does not produce a milky sap. It does produce numerous seeds, which can be reduced with annual aeration.
Ground ivy: Also known as creeping charlie, this weed is extremely difficult to control, as this creeping plant (recognized by its round, scalloped leaves, square stems, and small purplish flowers) can form large patches in shady, moist areas of the landscape.
Annual bluegrass: Annual bluegrass, also known as poa annua, is a bright green, low-growing grass that thrives in cool, moist weather. While it produces a number of white-colored seedheads and forms patches throughout the lawn, this weed is known to suddenly die out in hot, dry weather.