LEERSIA HEXANDRA Sw.

Family: Poaceae

Perennial; lax, ascending branched stems, 30-100 cm tall, nodes with distinct collar of white hairs; long rhizomes which form a dense mat; leaves flat, linear, to 20 cm long, midrib markedly scabrid below; ligule pale membrane. Inflorescence open panicle of ascending branches; spikelets oblong, 3.4-4.8 mm long.

Lowland and hydromorphic areas, moist soils or where flooding is shallow, drainage ditches and field margins; widespread and common. Unpleasant to remove by hand due to the risk of laceration from the scabrid midrib on the underside of the leaf.

It is widely spread in tropical countries of all over the world.

Countries: Burkina Faso, Thailand

PASPALUM CONJUGATUM Berg

Family: Poaceae

Common name: Carabao grass, Zacate amargo

Annual or perennial, culms spreading and branching below. Leaves flat, narrowly lanceolate, 8-20 x 0.5-1.2 cm. Spikes 2, terminal on slender peduncles; spikelets imbricate. It reproduces by seeds and flowers all the year.

It is a pantropical species and grows better in undisturbed soils. The plant is found in the settled areas, along trails, streams, and orchards.

Countries: Guyana, Costa Rica

PASPALUM DISTICHUM L.

Family: Poaceae

An erect or ascending perennial grass, with slender rhizomes and extensive stolons forming thick mats. The stem is much-branched, horizontal, giving rise to secondary roots. Leaves are flat or folded, 3-12 cm long, 2-6 mm wide usually hairy on the basal margins, sheaths loose, keeled, finely hairy towards the top and ligule 0.75-1.25 mm long. This weed has 2 (rarely 1 or 3) terminal erect to spreading spike-like racemes, up to 7.5 cm long, each bearing usually solitary greenish to yellowish spikelets in 2 rows along one side. The spikelets are appressed, elliptical and the upper glume hairy. The fruit is a brownish caryopsis.

It propagates mainly by creeping stolons and to some extent, by seeds. This weed is found in damp or wet situations, in wetland rice, and in dryland field crops and vegetables planted in bunded fields.

P. distichum is difficult to control because the detached stolon fragments regenerate easily and are tolerant of many herbicides. Stolons left on the soil surface for a while may be dessicated under the action of sun and air.

Countries: Iran, Nepal, Congo (Democratic)

PASPALUM SCROMICULATUM

Family: Poaceae

Perennial; tufted stems 15-100 cm tall; rooting at the lower nodes; leaves 5-30 cm long; ligule white membrane. Inflorescence 1-5 (-15) racemes bearing disc-like spikelets 1.5-3 mm across.

This plant is common in uplands, widespread in the forest and savanna zone.

Countries: Nepal, Togo, Vietnam,

Family: Poaceae

Perennial with creeping stems, 30-60 cm tall, stoloniferous; leaves stiff, ascending, 2.5-15 cm long. Inflorescence usually paired racemes, each about 1.5-7.5 cm long; spikelets ovate, flattened, 3-4.5 mm across.

P. vaginatum grows well in mangrove rice, coastal swamps and river deltas.

Countries: Sierra Leone

POTAMOGETON DISTINCTUS A. Benn

Family: Potamogetonaceae

A fleshy, broadleaf perennial weed, with a glabrous, shiny appearance. An aquatic perennial that grows in rice paddies, ditches, canals, marshes and ponds. It grows from May to October and flowers in July to August. Deep and/or prolonged flooding promote growth. It competes strongly with rice lowering yields and impeding water flow. Floating leaves are long petioled, alternate, lance-oblong to lance-elliptic. Submerged leaves are short-petioled, alternate, pellucid and thin, linear-lanceolate. Elongated flower stalks bear densely flowered spikes borne axillary from the stipules of floating leaves

It propagates by rhizomes and seed, but it spreads mainly by fast growing rhizomes and multiplies mainly by excised stems and overwintering scale-buds, formed several per rhizome.

Flooded rice is the most suitable environment for the growth of this weed. It is common throughout Korea.

It is rather difficult to control due to deep distribution of rhizomes in the soil and strong ability for regrowth. Stems are simple or short-branched.

Countries: China, Egypt

PHALARIS MINOR. Retz.

Family: Poaceae

Stem purplish; leaves dark green at the early stage. The length of internodes is more than wheat thus making it taller than wheat at maturity. P. minor has both tillering and branching which gives it a rosette shape.. A large number of seeds are shattered before harvest. Each ear head produces 400-600 seeds. The caryopsis is elliptic (oval) with a lateral embryo and soft endosperm. Seed colour varies from green (immature) to light yellow and glossy dark brown with hard seed coat. After harvest seed remains dormant for 6 months. Panicle is ovate-oblong , spikelets narrower not so conspicuously striped. The glumes are of 4-6 mm in length, the wing of the keel narrower; fertile lemma lance-ovate about 3 mm long, acute and sterile lemma solitary about 1 mm long. Propagation is by seed.

P. minor grows well in cultivated and waste places. It is a weed of many winter season crops, including wheat and barley. P. minor is common in Eurasia, South and North America, East and Southern Africa, and Australia.

It is controlled by several herbicides, the application rates of whom varies according to soil and growing conditions. Of the newer herbicides, P. minor is sensitive to fenoxaprop-P-ethyl, sulfosulfuron and clodinafop propargyl and provides satisfactory control under field conditions. Clethodim, sethoxydim, fluazifop-P-butyl, propachlor, metazachlor, atrazine and metribuzin can be used depending upon crop selectivity.

P. minor have evolved resistance to isoproturon in India; cross-resistance was also observed with diclofop-methyl.

Countries: India, Iran, Morocco, Nepal, Pakistan

PHYLLANTHUS AMARUS Schum. & Thonn.

Family: Euphorbiaceae

A slender, branched, glabrous annual herb, 20-60 cm high. Leaves oblong to elliptic, shortly petioled, rather pale beneath, 5-8 mm long. Flower axillary, corolla whitish or pale green, the sepals 5, green with white margins. Capsule 1.5-2 mm across. It reproduces by seeds.

A plant found in sub-tropical and tropical environments. It is a rare weed, mainly found in vegetables, legumes and other arable areas.

Conventional cultural methods are enough for its control.

Countries: Bahamas, Togo

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