Herbicide use and occurrence of Echinochloa spp. in rice fields in dry and intermediate zones of Sri Lanka.
Weed surveys were carried out in 251 rice fields in the dry and intermediate rice growing zones of Sri Lanka in 1994-95. All species within 5×5 m plots were identified and farmers interviewed regarding weed management practices. During October-December 1994, 132 weed species belonging to 32 families were identified in 176 fields. During April-August 1995, 96 different weeds belonging to 21 families were identified in 75 fields. In both seasons, Echinochloa colona [E. colonum] and E. crus-galli ranked among the 10 most important weed species, while E. frumentacea and E. stagnina occurred less frequently. Overall, frequencies of Echinochloa species were higher during the dry yala season (April-August). Canonical correspondence analysis revealed that E. crus-galli was a typical species in frequently-irrigated rice fields, whereas E. colonum was also frequent under drier regimes. The range of herbicides used was very limited, propanil and MCPA being the most frequently applied. Only 37.5 and 31.9% of interviewed farmers reported using the recommended doses of propanil and MCPA, respectively.