Weeds – Grasses

The best way to control weedy grasses is to eradicate as soon as you see young plants.  If they become established, it is best to dig them out, being careful to remove all the roots and stems as they can regrow from pieces that are left behind.  Spraying with regular house-hold vinegar may kill some of the weeds – please avoid using herbicides (especially Roundup) as they leave chemicals in the soil.

Bermuda Grass

A fine-textured, fast growing perennial. Bermuda grass spreads underground by rhizomes and above ground seeds and stolons.  Can be difficult to eradicate once established.

Bermuda grass is a low-growing, wiry perennial. The leaves are generally smooth and pointed with a conspicuous ring of white hairs at the junction of the blade and sheath.

Improved hybrids of Bermuda grass have been developed specifically for use as turfgrass. These hybrid varieties do not produce seed, whereas common Bermuda grass produces seeds that remain viable in soil for at least 2 years.

Control:  Not an easy weed to control, especially when it must be controlled selectively within an already planted garden or lawn. Dig clumps from flower beds before they form a mat.  Be sure to remove all the underground stems, otherwise it can start new shoots.  If the area is too large to dig (such as in a lawn), try spraying with regular household vinegar*.

 

Crabgrass

Shallow-rooted weed that thrives in lawns and flower beds that receive frequent surface watering, in underfed lawns, and in poorly drained fields.  As the plant grows, it branches out at the base – stems can root where they touch the soil.  Seed heads form in mid to late summer.  Smooth crabgrass will set seed even if mowed to just ¼ inch.  Large crabgrass is not as tolerant of close cutting, therefore, smooth crabgrass is more common.

Control:  Controlling crabgrass before it sets seed is important, because the seeds can remain viable for at least 3 years in soil. Pull before it makes seeds. Keep lawns well fertilized and vigorous to provide tough competition for weeds. To dry out roots, water lawns deeply, but not frequently.

 

Kikuyu Grass(Pennisetum clandestinum)

A vigorous perennial grass, sometimes used as a turf in coastal areas; spreads readily by rhizomes and stolons. Eventually forms an impenetrable mat of wiry stems. Leaves are medium green and covered in fine hairs.

An extremely aggressive perennial weed. Kikuyu grass is grows best under cool to warm temperatures (60° to 90°F) and moist conditions; however, it also survives well at high temperatures (100°F).  In coastal and some inland valley areas, kikuyu grass might not go dormant in winter. In other inland areas of California, it often turns brown in late November and remains dormant until spring, depending upon the temperature.

Growth can exceeding 1 inch per day, and a patch can expand an average of 4 square feet per month when growing without competition.  It seems to be most commonly spread by mowing, cultivation, and renovation equipment.

This is a prostrate plant that spreads by producing a network of thick, fleshy stems that root at the nodes. These stems often form a thick mat or thatch above the soil surface or a network of underground stems 1 to 4 inches deep in the soil. Mowing stimulates flowering.

Leaves of kikuyu grass are light green and 1 to 10 inches long. It has pointed leaf tips and flat leaf blades that are about 1/8 to 1/4 inch wide; It is often mistaken for St. Augustine grass, which has rounded leaf tips with sharply folded or creased leaf blades. Kikuyu grass leaves and stems are slightly hairy, while St. Augustine grass is smooth.

Control:  Maintain turfgrass and ornamental areas to assure they are at maximum vigor so that these plantings are as competitive as possible to help slow the invasion of this weed. Monitor areas and remove patches as soon as possible. Dense turfgrass and ornamental plantings shade the soil surface, making the establishment of kikuyu grass sprigs and seedlings more difficult, although it still may become established.

It is usually easier and more sustainable to maintain kikuyu grass as the turf species when it is it about 40% of the lawn. However, if you choose to renovate an entire lawn and replant with another turf species, solarization may be used as an alternative to herbicides.

Solarization may control infestations in areas that are to be replanted. For solarization to be effective, it must be used in full sun during the hottest part of the year (generally mid-July to mid-September for most of California), and the area must be kept covered with clear plastic mulch for 4 to 6 weeks. (See Pest Notes: Soil Solarization for Gardens and Landscapes in References.) It is unlikely that solarization will be effective in coastal locations due to seasonal fog and overcast skies.

 

Annual Bluegrass (Poa annua)

Common annual weed in lawns; easy to pull or hoe from flowerbeds.  Usually a cool-season lawn, but it dies off when rains lessens in the spring and temperatures rise.  Discourage it by maintaining thick turf grass.

It has light green flattened stems that are bent at the base and often rooted at the lower stem joint. Leaf blades are often crinkled part way down and vary from 1 to 3 inches long with typical Poa boat-shaped leaf tips. The boat-shaped leaf tips, which curve up like the bow of a boat, are a distinguishing characteristic.

Annual bluegrass has a fairly weak and shallow root system and needs frequent rainfall or irrigation to survive.

Control: Once a few annual bluegrass plants become established in turf or ornamental areas, spread can be rapid because of its prolific and rapid seed production. Mowing, foot traffic, birds, and cultivation all spread seed.

Hand pulling or hoeing to remove annual bluegrass can be effective as long as it is done frequently.

No single control procedure has been successful in controlling annual bluegrass in turfgrass. Early removal of solitary infestations has been successful when practiced diligently. Open spots should be overseeded to establish a vigorous turfgrass. Removal of grass clippings might help reduce the number of seeds that reach the soil.

Use deep and infrequent irrigation to discourage the development of shallow-rooted annual bluegrass.

Leaf blades that are crinkled part way down are a key characteristic of annual bluegrass

 

Nutsedge (Nutgrass)

The two most common species of nutsedge in California are yellow nutsedge, Cyperus esculentus, and purple nutsedge, C. rotun­dus. Yellow nutsedge grows throughout California, while purple nutsedge grows mostly in the southern portions of the state.

Nutsedge has three long, leaflike bracts at the base of each flower head. Yellow nutsedge has light brown flowers and seeds, while purple nutsedge flowers have a reddish tinge and the seeds are dark brown or black.

Although nutsedges resemble grasses and often are referred to as “nutgrass,” they aren’t grasses but are true sedges. Their leaves are thicker and stiffer than most grasses and are arranged in sets of three at their base; grass leaves grow across from each other in sets of two. Nutsedge stems are solid, and grass stems are hollow.

The upright, grass-like weed thrives in waterlogged soil, and their presence often indicates drainage is poor, irrigation is too frequent, or sprinklers are leaky. Once established, however, they will tolerate normal irrigation conditions or drought. It can be identified by its bright green, ¼-inch-wide leaves with a conspicuous midvein. Flower head is golden brown. Small, roundish tubers may be found at the root tips. Spreads by tubers or seed.

Control:  Once established, nutsedge plants are difficult to control.  Prevent establishment by removing small plants before they develop tubers.  The majority of tubers occur in the top 6 inches of soil, but can grow as deep as 14 inches.  Tubers can survive in the soil for up to 3 years.

A weed often confused with yellow or purple nutsedge is tall umbrella sedge, (Cyperus  eragrostis), another perennial sedge that grows in wet, soggy soils. Tall umbrella sedge is a large, light green sedge that doesn’t produce tubers. It spreads by seed or by new plants that form on short, thick rhizomes around the base of the mother plant. If left unmowed, it grows taller than nutsedge, but in a mowed turf you can distinguish it from nutsedges by its tendency to grow in tight clumps that are less than 1 foot in diameter, its wider leaves and stems, and its short, thick rhizomes and lack of tubers.

Another weed often confused with nutsedges is green kyllinga, Kyllinga brevifolia, which also is a major problem in turf and ornamental plantings. (See Pest Notes: Green Kyllinga in References.) Green kyllinga flowers are visibly different from those of nutsedges, and the plant produces rhizomes but not tubers.

 

Happy Gardening!

Lisa

An Hour to Garden

2014