Eclipta prostrata
(eclipta)

A native of Asia, now widely distributed in the tropical, subtropical and warm temperate regions (Holm et al., 1977). It is spread as a contaminant in rice seed in the Philippines (Rao and Moody, 1990) and is thought to have been introduced into France in contaminated seed (Jauzein, 1991). Seeds are carried from field to field by running water especially during the flooding period (Quisumbing, 1923).

E. prostrata occurs under both upland and lowland conditions. It is widespread in damp places (heavy soils with a constant and abundant water supply are preferred - Kranz et al., 1977), in ditches, and near rivers and swamps. It is a common weed of rice. However, its occurrence in lowland rice fields may be determined entirely by water management (Lee and Moody, 1988a).

E. prostrata is propagated by seed, and is a C3 species.

Garcia (1931) reported that seeds of E. prostrata failed to germinate when the moisture content of the germinating medium was as low as, or lower than, 30% saturation. As the moisture content increased, there was a corresponding increase in the percentage germination. According to Vongsaroj (1991), field capacity is ideal for germination of E. prostrata. E. prostrata is more sensitive to moisture stress than rice (Lee and Moody, 1988a).

Achenes of E. prostrata show no pronounced innate dormancy (Ramakrishnan, 1960; Lee and Moody, 1988b) (both ripe and unripe seeds germinate - Gupta, 1992). Germination is not affected by pH (Lee and Moody, 1988a) nor water quality (Gupta, 1992).

However, light is required for the germination of seeds of many weed species including E. prostrata. Lee and Moody (1988a) reported that there was no germination of E. prostrata achenes in the dark or when they were exposed to green, blue or far-red light, but germination under red and yellow light was as good as that under white light. In an upland soil, 74% of the achenes planted on the soil surface germinated, 18.5% emerged when planted 0.2 cm deep, and no emergence was observed at planting depths of 0.5 cm or greater. Under flooded conditions (2 or 5 cm deep), about 9% of the achenes germinated when planted on the soil surface and no emergence was observed when the planting depth was 0.2 cm or greater. Lee and Moody (1988a) noted that no germination of E. prostrata achenes occurred in the absence of oxygen.

Germination of E. prostrata is also significantly improved by alternating temperatures (Lee and Moody, 1988a). At a constant temperature of 35°C, 78% of the achenes germinated whereas at alternating temperatures of 35/20°C with a 12-h thermoperiod, there was 96.5% germination. Germination of E. prostrata achenes is also influenced by the duration of illumination after absorption of water. Ten hours' illumination was needed for maximum germination and 2 h for 50% germination. There was no germination with exposure to light for 30 min or less (Lee and Moody, 1988a).

Flowering of E. prostrata started during the fifth week after emergence, and mature achenes were produced from the sixth week (Lee and Moody, 1988b). Usually 10-14 days were required for the achenes to mature. About 200 inflorescences and 14 000 achenes were produced per plant. (Seed weight: 0.292 mg/seed - Pancho and Kim, 1985).

Weber et al. (1995) reported that as soil fertility declined in maize-based cropping systems with a high frequency of cereal cropping and a low frequency of cereal cropping in the northern Guinea savanna in Nigeria, E. prostrata became a more important component of the weed flora. Oka (1988) also reported that E. prostrata benefitted from the impact of environmental stresses at a coastal site subject to saline winds following the destruction of a windbreak forest. E. prostrata is tolerant of highly polluted places (Rao et al., 1983) and has high salt adaptability (Choudhuri and Varshney, 1975; Varshney and Sharma, 1979). Lee and Moody (1988a) reported that there was 81.5% germination of E. prostrata achenes in 0.8% NaCl solution and 13.5% germination in 1.6% NaCl solution.

E. prostrata is reported to be a host of rice sheath blight Rhizoctonia solani [Thanatephorus cucumeris] (Kardin et al., 1977; Kannaiyan and Prasad, 1980); Sclerotinia blight of groundnut, Sclerotinia minor (Melouk et al., 1992); dry root rot of chickpea, Macrophomina phaseolina (Singh et al., 1990); and tobacco necrosis satellivirus which also causes tulip necrotic disease (Nahata and Kusaba, 1979).

E. prostrata is an alternative host of Amsacta moorei which also feeds on newly emerged sorghum and castor bean (Ricinus communis) (Agarwal et al., 1989) and of the girdle beetle, Oberea [Obereopsis] brevis (Shrivastava et al., 1989).

It is an alternative host of the root-knot nematodes Meloidogyne incognita (Soerjani et al., 1987) and M. graminicola (Rao et al., 1970); the ring nematode Criconemella onoenis; Tylenchorhynchus claytoni (Satyanarayana Prasad et al., 1980); the rice root nematode Hirschmanniella oryzae (Mathur and Prasad, 1973); and the corn cyst nematode Heterodera zeae (Parihar et al., 1991).

Variability

In Japan, Umemoto et al. (1987a) reported two types of E. prostrata based on morphological differences of their leaves and achenes. These variations were attributed to the soil moisture conditions in the different habitats. Photoperiodic flowering response was approximately related to the latitudinal differences in the habitats and was not related to morphological differences. Strains collected from Honshu did not flower under 16 h daylength (qualitative short-day response) whereas those collected from Okinawa flowered in the same number of days both under natural daylength and long daylength (quantitative short-day response). One strain collected from Taiwan showed a day-neutral response (Umemoto et al., 1987b).

Lee and Moody (1989a) collected 14 ecotypes of E. prostrata from different habitats in the Philippines. There were differences in growth type and leaf characteristics, reproductive characteristics, and morphological characters among ecotypes. Using cluster analysis, the 14 ecotypes were classified into four groups, lowlands, uplands, mountainous roadsides, and high altitudes and specific soils. The ecotypes from the mountainous roadsides had the largest shoot weight and produced the largest leaves. The upland ecotypes had serrate leaf margins and the highest achene production. The ecotype from the saline soil had the smallest and the thickest leaves; that from high altitude was a short plant with high achene production.

Dissimilarities among the ecotypes did not necessarily correspond with their geographical habitats. For example, the Tarlac ecotype was similar to those from the lowlands despite the fact that it was from an upland habitat, while the Iloilo ecotype was similar to those from the mountainous roadsides although it was from a lowland area.

Thus E. prostrata has a high dispersability and a high adaptability to changing environmental conditions. Ecotypic variations may be an adaptation response to differences in geographical, edaphic, climatic and biotic factors.

Moody et al. (1994) observed Altica sp. feeding on E. prostrata in South Cotabato, Philippines.

Medicinal, pharmaceutical

• Traditional/folklore

E. prostrata is not readily confused with any other common weed species but if necessary, useful distinguishing features include the white flowers, the two-rowed involucral bracts and the absence of pappus (Holm et al., 1977).

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Introduction

Early control is necessary to prevent competition from this rapidly growing weed (Kranz et al., 1977). In drill-seeded rice in Arkansas, it did not compete with rice during the early season but lowered grain yields when competing with rice during mid- to late-season (60-120 days after emergence). Thus, control by mid-season is essential to prevent yield losses (Smith, 1988b).

Cultural Control

Germination and growth of E. prostrata in lowland rice are suppressed by flooding for 3-4 weeks after planting. Lee and Moody (1988b) reported that seedling growth of E. prostrata was greatly reduced when flooding occurred at or before the four-leaf stage. Flooding at the four-leaf stage resulted in a 53% reduction in plant height compared to the unflooded control. In contrast, seedlings flooded at the six-leaf stage were 51% taller than those in the unflooded control at 40 days after emergence. Seedlings at the six-leaf stage, which appears to be a critical stage, or older became acclimatized and persisted under flooded conditions. Garcia (1931) noted that seedlings 2.5 cm tall were quite resistant to flooding. Singh et al. (1983) reported that submergence of E. prostrata at the vegetative stage with 90 cm water for 4 days caused defoliation of all of the leaves except the terminal leaf; E. prostrata at the flowering stage was unaffected by submergence.

E. prostrata is easily controlled by hand pulling and cultivation. Vigorously growing lawn grass soon causes its disappearance from ornamental turf (Pope, 1968).

Chemical Control

E. prostrata is susceptible to paraquat (Madrid et al., 1972), 2,4-D, oxadiazon (Terry, 1983), fenoxaprop-ethyl, thiobencarb + fenoxaprop-ethyl, propanil + lactofen (Khodayari and Smith, 1985), thiobencarb + fenoxaprop, propanil + esprocarb, propanil + fenoxaprop (Smith, 1988a), bentazone + quinclorac (Sabri Gamil Ahmed et al., 1989), molinate + 2,4-D (Srinivasan and Pothiraj, 1989), imazethapyr (Wilcut et al., 1991), acifluorfen + bentazone, lactofen (Jordan et al., 1993a), clomazone + fluometuron, clomazone + pendimethalin + fluometuron (Jordan et al., 1993b), anilofos + 2,4-D (Rao, 1995), rimsulfuron (Bewick et al., 1995) and ethalfluralin (Grichar and Porteous, 1996). It is moderately resistant to butachlor, fluorodifen (superseded), thiobencarb (Terry, 1983) and trifluralin (Madrid et al., 1972). Ampong-Nyarko and de Datta (1991) also indicate resistance to fenoxaprop and piperophos; moderate resistance to butachlor, fluorodifen (superseded), oxadiazon, propanil and thiobencarb; and susceptibility to bentazone, 2,4-D, MCPA, glyphosate, oxyfluorfen and paraquat. Contradictory results have been reported as to its level of susceptibility to atrazine and its level of resistance to propanil (Madrid et al., 1972; Terry, 1983).