Occurrence and Control of Weeds in Direct-seeded Rice Paddy in Korea.

Abstract

The planted area of direct-seeding rice cultivation in Korea, which began in 1991, increased remarkably up to 117, 500 ha in 1995, but decreased to 63, 900 ha in 1998 and then rose to 71, 700 ha in 1999. Farmers preferred dry paddies to flooded paddies at first for direct-seeding, but in recent years this has changed due to frequent rainfalls at seeding time. The number of weed species occurring in paddy fields in Korea was 23 in direct seeding on dry paddy and 18 in direct-seeding on flooded paddy. Echinochloa crus-galli was the most dominant weed species in direct-seeding on dry paddy and was followed by Cyperus difformis, Cyperus serotinus, Ludwigia prostrata and Aneilema japonica. The dominant weed species in direct-seeding on flooded paddy were Echinochloa crusgalli, Eleocharis kuroguwai, Scirpus hotarui, Monochoria vaginalis and cyperus difformis. On the contrary, Eleocharis kuroguwai, Sagittaria pygmaea, Sagittaria trifolia, Echinochloa crus-galli and Monochoria vaginalis were dominant weeds in machine transplanted paddy fields. Occurrence of weedy rice, especially red rice, was also increased greatly in directly-seeded rice fields, although effective herbicides or other practical control methods are not yet developed. The recommended herbicide application for controlling weeds in direct seeded dry paddies and flooded paddies in Korea is the systemic application of two time points: before and after water logging, in case of medium weed occurrence. Additional application is recommended for heavy weed occurrence. It seems that direct seeding is one of the most attractive rice cultivation techniques for labor and cost saving. However, it is still an unstable technique because of poor seedling establishment, more occurrence of weedy rice, lodging problem and lack of satisfactory seeding machines. Direct-seeding rice cultivation is expected to increase in future by farmers in Korea who understand the technique better.