Integrated Management of Paddy Weeds in Korea, with an Emphasis on Allelopathy
Annual weeds such as Echinochloa crus-galli and Monochoria vaginalis, and perennials such as Sagittaria trifolia, Sagittaria pygmaea, Eleocharis kuroguwai, Cyperus serotinus and Potamogeton distinctus, have been the most important weed species in paddy fields in Korea during the past two decades. Perennial weeds have increased from about 19% in 1971 to about 54% in 1981 and 60% in 1990. E. kuroguwai and S. trifolia are now the weeds most resistant to current herbicides, because their emergence takes place over a prolonged period. Biocontrol of E. kuroguwai has become possible by means of a plant pathogen, Epicoccosorus nematosporus, and of Scirpus planculmis by a pathogen Alternaria sp.. Residues of crops such as barley, wheat and rye had the allelopathic potential to reduce a population of P. distinctus in paddy fields. Phenolic compounds found in crop residues such as ferulic acid have been determined to have allelopathic potential, and also p-coumaric, sinapic, protocathechuic and caffeic acids. The integration of efficient herbicides with cultural control (using crop rotation, appropriate cultivation methods, crop residues etc.) and biocontrol (use of plant pathogens such as E. nematosporus and Alternaria sp.) can help make integrated weed management (IWM) a reality in Korea's rice production.