A nice lawn can not only add to the appearance of your home, it can also prevent soil erosion and help to absorb heat and noise. However, invading weeds will often spoil lawn evenness and appearance. Weeds, which are often introduced through vehicles, human and animal movement or via the wind, compete with the lawn for water and nutrients. Control of these weeds can be difficult in a lawn situation, where manual removal may be ineffective and selective chemicals are required to ensure protection of the lawn itself. This Gardennote aims to provide information on the most common weeds in lawns and the methods used to control them. Weeds can be divided into broadleaf weeds, grasses and sedges.
Jo-jo or Bindii
Jo-jo (Soliva sessilis) is a mat forming annual weed that first emerges with the winter rains in May. Flowers are inconspicuous and are produced in spring at the base of the leaf axils. Seeds harden and become brown when mature, developing short, sharp spines which can make it impossible to walk barefooted on badly infested lawns.
Burr Medic (Medicago polymorpha) is an annual weed that can often invade lawns. It is usually hairless, with stems up to 60 cm long, and having clusters of two to seven flowers borne on short stems in winter and spring. The leaflets are oblong to heart shaped. The seed pods or burrs are like disc, or cylindrical in shape, and consist of oneto six coils that are densely spined. These burrs when mature and brown can often be painful to step on and attach easily to clothing like socks and shoes and also to pet hair, where the seeds are then spread to other areas.
Carrot weed (Cotula australis) is a native annual species with fern like leaves, and is often mistaken for Jo-jo at first glance due to its similar appearance. However unlike Jo-jo which produces its green flowers at the base of the leaves with no stalk, carrot weed flowers are white to pale yellow and occur on long slender stalks.
Caustic weed/eyebane/spotted spurge
Caustic weed (Chamaesyce drummondii (syn. Euphorbia drummondii)) is a prostrate multibranched annual weed that infests both gardens and lawn areas. The leaves are circular to oblong shaped and often have a purplish blotch in the centre. The flowers are inconspicuous and small and are often tinged pink. Flowers appear in summer to autumn.
There are many varieties of clover but white clover (Trifolium repens) is most commonly found infesting lawns. It is a prostrate perennial weed that has stems up to 30 cm long and has the ability to spread by rooting at each node. This makes removal difficult as any portion left behind has the ability to keep growing. Leaflets are oval to rounded, trifoliate, with a pale crescent on the upper surface. Flowers can be white, yellow or pink and occur in a cluster on slender stalks above the foliage. Flowers are borne in spring and summer.
Dandelion (Taraxacum officinale) is an increasingly common weed in lawns in Western Australia. It is a perennial, with a strong taproot and a rosette of toothed leaves. The stems are hollow, with only ever one flower head per stem. The distinctive flowering heads, which can be produced throughout the year, are 3 cm across, contain yellow florets and are followed by a sphere of plumed parachute seeds. The plant exudes milky latex if cut.
Flatweed (Hypochaeris spp.) is an annual or short lived perennial that is very common in lawn and garden situations. There are two species: Hypochaeris radicata which consists of a basal rosette of rough, bristly leaves and yellow dandelion like flowers at the tops of slender leafless stalks, and Hypochaeris glabra which is very similar in appearance, with the exception of the leaves being smooth and having slightly smaller flower heads. They can often be hard to tell apart, with many hybridising freely. Flowers may appear all year round but are most common in spring. Seeds form after flowering, with both species having feathery hairs (pappus) which enables seeds to spread readily via wind dispersal.
Cudweed (Gamochaeta calviceps) is an annual herb with a densely woolly, spike-like, leafy inflorescence. The leaves are spoon-shaped and somewhat woolly, and the flowers golden-brown.
Fleabanes (Conyza spp.) are upright annual herbs of various heights. They are typically grey-hairy plants. The stems branch below each pyramid of inflorescences resulting in a candelabra shape. Fleabanes flower in summer and are prolific seed producers. Each plant produces up to 110,000 seeds and the pappus on the seed enables it to be dispersed long distances by wind.
Among the mouse-eared chickweeds, Cerastium glomeratum is the most common weed of lawns. It is an annual weed. The flowers, produced in spring and early summer, are in clusters with white, notched petals, which often do not fully open. The leaves are ovate and the plant is densely hairy all over.
Creeping oxalis/wood sorrel
Oxalidaceae, the wood sorrels, are a family of perennial herbs, that regrow annually from tubers, bulbs or corms. The leaves usually consist of three heart shaped leaflets, similar to clover.In the metropolitan area, creeping oxalis (Oxalis corniculata) is a common lawn weed. It is highly branched with a lightly fleshy taproot, producing slender stems that creep horizontally, rooting at intervals and with leaves along the stem. Small yellow flowers in clusters of one to six arise on stalks from the leaf axils. Creeping oxalis flowers in spring and summer. Other wood sorrels common in lawns are O. perennans, which has larger flowers and O. pescaprae which is known as soursob or sourgrass.
Summer grass (Digitaria ciliaris) is an annual weed of lawns with spreading stems that grows close to the ground. Leaves are soft and hairy. A feature of this grass is the inflorescences which are 20–80 cm tall. They are composed of conspicious seed heads found at the ends of slender stalks.
Mullumbimby couch (Cyperus brevifolius) forms extensive rhizomatous patches in overwatered lawns and garden beds. It has bright green, shiny, grass-like leaves and may be mistaken for a lawn grass until it flowers in summer (often only on the margin of mown areas).
Parramatta grass (Sporobolus africanus) is a tufted perennial with basal leaves, to 50 cm tall. The dense, narrow inflorescence is dark green, flat, spike-like, to 20 cm long, produced from November to June. It is a lawn weed from Perth to Albany.
Winter grass (Poa annua) is a tufted annual grass, usually about 10 cm tall. It produces pale-greenish seed heads, mainly winter and spring, but can also flower in summer. It is a common weed in gardens and lawns.
Guildford Grass/Onion Grass
Guildford grass (Romulea rosea) is the most common of plants which grows from corms.
The flowers, with petals up to 1.8 cm in length, open first at ground level. As they mature, the flower stem elongates and bends over, eventually pushing the seed capsule back under the surrounding leaf litter.
Herbicides should be applied via a sprayer, dedicated to herbicides only. Avoid spray-drift and if other garden plants are contaminated, use a garden hose to wash the chemical off thoroughly.
Selective, pre-emergence herbicides are typically used to control annual weedy grasses and some annual broadleaf weeds in lawns. To control winter grass, pre-emergence herbicides need to be applied in autumn and winter, before the weeds have germinated. A regular application every 6 to 8 weeks will also control summer grass. Commonly available garden products contain pendimethalin or propyzamide.
Selective, post-emergence broadleaf herbicides can be used to control broadleaved weeds in lawns. Commonly available garden products contain one or more of the following active ingredients: MCPA, dicamba, DSMA, Bentazone, Bromoxynil, Mecoprop, 2,4-D, clopyralid.
Make sure that the products being used state on the label that they are for use on your variety of lawn and will control the targeted weed.
Look at the other posts and pages on the blog, you might be interested.
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