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Weedy Rice Observatory

Weedy rice is a troublesome weed widespread all over the world. Weedy rice includes a range of biotypes belonging to numerous species. The wild species Oryza barthii and O. longistaminata or weedy biotypes from the cultivated O. glaberrima are among the worst weeds in West Africa and Sahel. O. granulata, O. officinalis, O. rufipogon and O. nivara can give severe infestation in Vietnam and other South-East Asian countries. Red rice is the most common weedy biotype of the cultivated rice (Oryza sativa var. sylvatica) in all rice growing areas with temperate climate. Known in Italy since the last century, and for some time considered as a pathologic strain of the crop, red rice shows a wide variability of anatomical, biological and physiological features. At seedling stage, red rice plants are difficult to distinguish from the crop, while after the tillering the identification of the weed is possible thanks to many gross morphological differences in comparison with the rice varieties: more numerous, longer and more slender tillers, leaves which are often hispid on both surfaces, tall plants, pigmentation of several plant parts (in particular of the pericarp), easy seed dispersal after their formation in the panicle. The break off of the seeds onto the soil before crop harvesting allows the weed to disseminate and feed the soil seedbank. The spread of red rice became significant mainly after the shift from rice transplanting to direct seeding, and started to be very severe, particularly in European Countries over the last 15 years after the cultivation of weak, semidwarf indica-type rice varieties. At present, the spread is mainly related to the planting of commercial rice seeds containing grains of the weed. The weed affects rice yield because of its high competitive capacity. The red layer of the weed grains harvested with the crop have to be removed with an extra milling but this operation results in broken grains and grade reduction.The close similarity between red rice and the commercial varieties has prevented the application of herbicides that are able to selectively control the weed. The main weed control strategies that are applied by rice growers are those of the planting of clean seeds, chemical or mechanical control both in pre- and post-emergence of red rice in crop pre-planting (e.g. with the stale seed bed technique) or in crop post-planting (e.g. by cutting the panicle) and rotation. In most cases, two or more of these strategies are combined. In some conditions, the weed pressure is so high that the only way to reduce red rice populations is to adopt rotation, although, this practice shows some constraints in particular environmental conditions such as in the presence of saline and hydromorphic soils.

Research
The seriousness of red rice problem induced the European Commission to fund a 3-years research project (known with the acronym BICORER) aimed at studying the biology and control of the weed. The project coordinated by the Dipartimento di Agronomia of Turin University, includes 11 institutions of main European rice growing countries: Italy, France, Portugal and Greece.
Main results of this research are reported in the issue n. 9 of Medoryzae included in this site.

International meetings
FAO Global Workshop on Red Rice Control (Taller Global de Control de Arroz Rojo). Varadero, Cuba, 30 August-3September 1999.
Coordinator: Ricardo Labrada Romero (ricardo.labrada@fao.org)

Literature

Some basic literature on weedy rice is reported hereafter.

Baker J.B., Sonnier E.A., Shrefler J.W., Integration of molinate use with water management for red rice (Oryza sativa) control in water-seeded rice (Oryza sativa), Weed Sci. 34 (1986) 916-922.

Català M., Chemical and cultural practices for red rice control in rice fields in Ebro Delta (Spain), Crop prot. 5 (1995) 405-408.

Chancellor R.J., The depth of weed seed germination in the field, in: Proc. Br. Crop. Prot. Conf. Weeds (1964) 607-613.

Chon M.A., Hughes J.A., Seed dormancy in red rice ( Oryza sativa) 1. Effect of temperature on dry afterripening, Weed Sci. 29 (1981) 402-404.

Craigmiles J.P., Introduction, in: E.F. Eastin (Ed.), Red rice research and control, Tex. Agric. Exp. Stn. Bull., 1978, 5-6.

Diarra A.R.J., Smith R.J., Talbert R.E., Interference of red rice (Oryza sativa) with rice (O. sativa), Weed Science 33 (1985) 644-649.

Diarra A.R.J., Smith R.J., Talbert R.E., Growth and morphological characteristics of red rice (Oryza sativa) biotypes, Weed Science 33 (1985) 310-314.

Eastin E.F., Additional red rice research, in Texas in: E.F. Eastin (Ed.), Red rice research and control, Tex. Agric. Exp. Stn. Bull., 1979, 30-34.

Fay P.K., Olson W.A., Technique for separating weed seed from soil, Weed Sci. 26 (1978) 530-533.

Ferrero A., Finassi A., Vidotto F., Prediction of red rice seedling densities from seed bank, Meded. Fac. Landbouwwet. Rijksuniv. Gent (1996) 1181-1187.

Ferrero A., Vidotto F., Balsari P., Airoldi G.F., Mechanical and chemical control of red rice (Oryza sativa L., var. sylvatica) in rice (Oryza sativa L.) pre-planting. Crop Protection (1999) 18, 245-251.

Footitt S., Cohn M.A., Seed dormancy in red rice, Plant Physiol. 100 (1992) 1196-1202.

Footitt S., Vargas D., Cohn M.A., Seed dormancy in red rice.X. A 13C-NMR study of the metabolism of dormancy-breaking chemicals, Physiol. Plant. 94 (1995) 667-671.

Ghesquière A., Andre F., Feougier G., Braun P., Un riz adventice, in: ITCF, (Ed.), Riz: Du débouché à la culture, 1995, 41-44.

Goss W.L., Brown E., Buried red rice seed, J. -Am. Soc. Agron. 31 (1939) 633-637.

Grundy A., Mead A., Bond W., Modelling the effect of weed-seed distribution in the soil profile on seedling emergence, Weed Res. 36 (1996) 375-384.

Hoffman M.L., Owen M.D.K, Buhler D.D, Effects of crop and weed management on density and vertical distribution of weed seeds in soil, Agron. J. 90 (1998) 793-799.

Kwon S.L., Smith R.J., Talbert R.E., Comparative growth and development of red rice (Oryza sativa) and rice (O. sativa), Weed Sci. 40 (1992) 57-62.

Leopold A.C., Glenister R., Cohn M.A., Relationship between water content and afterripening in red rice, Physiol. Plant. 74 (1988) 659-662.

Ogg A.G. jr, Dawson J.H., Time of emergence of eight weed species, Weed Sci. 32 (1984) 327-335.

Pantone D.J., Baker J.B., Weed-crop competition models and response-surface analysis of red rice competition in cultivated rice: a review, Crop Sci. 31 (5) (1991) 1105-1110.

Rahaman A., James T.K., Patterns of weed seedling emergence in two new Zealand soils, in: Proceedings 8th EWRS Symposium "Quantitative approaches in weed and herbicide research and their practical application", Braunschweig, 1993, 665-672.

Roberts H.A., Feast P.M., Fate of seeds of some annual weeds in different depths of cultivated and undisturbed soil, Weed Res. 12 (1972) 316-324.

Saavedra M., Garcia-Torres L., Hernandez-Bermejo E., Hidalgo B., Influence of environmental factors of the weed flora in crops in the Guadalquivir valley, Weed Res. 30 (1990) 363-374.

Sagarra J., Importancia del conreu de l’arròs a Catalunya. Produccions i aprofitaments, in: L’arròs tecniques, Fundacio’ La Caixa, Amposta, 1987, 7-10.

Seshu D.V., Sorrells M.E., Genetic studies on seed dormancy in rice, in: Rice Genetics, IRRI, Manila, 1986, 369-382.

Smith, R.J. jr., Control of red rice (Oryza sativa L.) in water seeded rice (Oryza sativa L.), Weed Sci. 29 (1981) 61-62.

Stoller E.W., Wax L.M., Temperature variations in the surface layers of an agricultural soil, Weed Res. 13 (1973) 273-282.

Tarditi N., Vercesi B., Il riso crodo: un problema sempre più attuale in risicoltura. Inf. Agrar. 49 (11) (1993) 91-95.

Vidotto F., Ferrero A., Germination behaviour of red rice (Oryza sativa L.) seeds in field and laboratory conditions. Agronomie (2000) 20, 375-382.

Last update: 23/04/03