Weed Biology and Management 2, 194–199 (2002) RESEARCH PAPER Propanil-resistant barnyardgrass [Echinochloa crus-galli (L.) Beauv.] in Sri Lanka: Seedling growth under different temperatures and control B. MARAMBE* 1 and L. AMARASINGHE 2 1 Department of Crop Science, Faculty of Agriculture, University of Peradeniya and 2 Plant Protection Service, Department of Agriculture, Ministry of Agriculture, Peradeniya, Sri Lanka Experiments were conducted to (i) evaluate the efficacy of propanil formulations available in Sri Lanka in controlling Echinochloa crus-galli; (ii) study the seedling growth of propanil- resistant (R) and -susceptible (S) biotypes of the weed under different temperatures; (iii) quan- tify the level of resistance in R biotypes and; (iv) to suggest alternative control measures for R biotypes. Field studies showed that retail propanil formulations (36% a.i., EC) applied at 2.7kg a.i. ha -1 gave less than 30% control of E. crus-galli collected from several locations of the north dry zone of Sri Lanka. Chemical analysis revealed that there was no adulteration of propanil formulations at the retailer level. Growth studies conducted in controlled environments indi- cated that per cent germination and seedling growth of R and S biotypes were similar at the day/night temperature regimes imposed. However, per cent germination for plants grown under a 34/31∞C (day/night) regime was 27–29% higher compared to those grown at 28/ 24∞C. At the higher temperature regime, R and S biotypes reached the 2–3 leaf stage five days earlier, and the 4–5 leaf stage seven days earlier. The ED 50 values from the dose–response experiments indicated that the R biotype was four times more resistant to propanil than susceptible ones. The resistance index (RI) did not vary significantly under different temperature regimes. Quinclorac (25% a.i., SC) applied at 200 g a.i. ha -1 and bispyribac-sodium (10% a.i., SC) applied at 30 g a.i. ha -1 (recommended dosages) successfully controlled propanil-resistant biotypes of E. crus-galli. Conversely, oxadiazon and propanil (8% and 23% a.i., EC, respectively) applied at 280 + 805 g a.i. ha -1 did not result in satisfactory control. Keywords: barnyardgrass, propanil-resistant weeds, rice, Sri Lanka. the productivity of rice, which has shown yield stagna- tion during the past decade (Abeysekara 1999). Esti- mates from farm surveys have indicated that weeds accounted for about 40% yield loss in rice compared to 10.2% due to insect pests, 1.2% due to diseases, 28.2% due to floods, and 20.4% due to other abiotic factors (Herath Banda et al. 1998). Most of the rice in Sri Lanka is direct-seeded and grown in the dry zone, especially the north central province (Amarasinghe & Marambe 1998). Barnyardgrass [Echinochloa crus-galli (L.) Beauv.] is a major weed in lowland rice cultivation in many parts of the world, including Sri Lanka. The competitive pressure *Correspondence to: Buddhi Marambe, Department of Crop Science, Faculty of Agriculture, University of Peradeniya, Sri Lanka E-mail: bmarambe@cropsci.pdn.ac.lk Received 21 June 2001; accepted 31 July 2002 INTRODUCTION Rice (Oryza sativa L.) is the major staple food crop in Sri Lanka and rice agriculture is the main source of employ- ment for the majority of the rural population (Central Bank 2000). However, yield losses due to biotic and abi- otic stresses have been identified as major constraints to Blackwell Science, LtdOxford, UK WBMWeed Biology and Management1444-61622002 Weed Science Society of Japan 204December 2002 068 Propanil-resistant barnyardgrass in Sri Lanka B. Marambe and L. Amarasinghe 10.1046/j.1444-6162.2002.00068.x Research Paper194199BEES SGML