臺灣之稻作採水田栽培，其耕作面積及生產量均為各作物之首。水田由於經常處於湛水之狀況，適於水生及水陸生雜草之發生。其雜草相與旱田者迴然不同。本省文獻中所記錄之水田雜草有42科165種。其草相組成與地緣相鄰之我國大陸、日本、韓國、及菲律賓相近。全省性發生而危害程度大者為鴨舌草、稗草、球花蒿草、野茨菰及螢藺等5種草。重要性次之者包括母草、定經草、印度水豬母乳、水莧菜、喇叭草、田字草、雙穗雀稗、兩耳草、木蝨草、牛毛氈、鱧腸、滿天星及瓜皮草等13種。部份雜草如野茨菰、螢藺、瓜皮草等其發生呈明顯之地區性差異。以栽培季節言，野茨菰等在一期作較多，鴨舌草及印度水豬母相在二期作較多，而多數之雜草兩期作中之發生相似。本省水田於1960年代中期開始使用殺草劑，至1978年其使用率已達總面積之91.2%。殺草劑使用後水田一年生雜草減少。萌前殺草劑不能有效防治之多年生雜草則增加，估計目前雙穗雀稗、野茨菰、螢藺、滿天星及牛毛氈等多年生草之發生均在10萬公頃以上(兩期作面積合計)，極具危害之潛力。稗草及鴨舌草有差異很大之種內變異，其在危害及防治上之意義值得探討。多種水稻病蟲害之病原及害蟲原以雜草為寄主植物，水田及四週環境中之雜草可以增加病蟲之發生機會及危害程度。水田雜草對及養分之競爭可直接引起水稻減產。競爭性危害在二期作中較嚴重。不防治雜草之狀況下，兩期作之平均減產在直播及移植稻分別為62%及16%。目前雖因防治澈底，田間之實際損失輕微，但卻是鉅額殺草劑及人工除草費用(1979年達13.6億新臺幣)所換得。由於農村勞力缺乏及經營利潤微薄，水稻之栽培日益粗放，水田雜草防治須發展更經濟有效之方法。雜草之研究急待加強才能因應此種情勢。

In literatures, 165 species of plants, belong to 42 families, have been recorded as weeds in paddy field in Taiwan. Weed flora resembles those of the neighboring areas such as mainland China, Korea, Japan, and Philippine. The most important weeds are Monochoria vaginalis, Echinochloa Crus- galli, Cyperus di f f ormis, Sagitzaria tri/olia, and Scirpus [uncoides for their wide distribution and great damaging capability. Common and moderate important weeds are Lindernia pyxidaria, L . anagallis, Rotala indica, Ammania bacci f era , Ludwigia prostrata , Masilea quadri f olia, Paspalum distichum, P. con jugatum , Fimbrystylis miliacea, Eleocharis acicularis, Ecli pta prostrata, Alternanthera sessilis , and Sagittaria pygmea. For the majority of weeds, their occurence in terms of frequency and vegetative growth is similar between the first and the second rice season. However, some weeds are season specific or appearing more either in the first or the second rice season. Distribution characteristics of paddy weeds are presented and their causing reasons explored. Herbicides have been used in paddy field since the middle 60's. In 1978, herbicide treated field occupied 91 % of the total rice hectage , Perennial weeds not effectively controlled by granular herbicides have increased after the use of herbicides. We estimated that in 1980, the occurrence of 5 major perennial weeds, Sagittaria trif olia , Paspalum distichum ; Scirpus [uncoides , Alternanthera sessilis, and Eleocharis acicularis were all exceeding 100,000 ha in a total of 636,000 ha of cult i vated hectage. The control of perenn ia 1 weeds are becoming the major concern of farmers and research workers. Sub-species taxa of EchinochJoa crus-gaili and Monochoria vaginalis which show significant difference in growth and flowering characteristics have been found, and project has initiated to investigate their significance in associated with control. In Taiwan, 7 kinds of rice insects and 6 ttinds of rice disease pathogens have been reported able to host on weeds. Indirectl y, weeds affect rice by increasing the seriousness of pests and complicating their control. Data of long term and multi-sites trials indicated that under competition, rice grain yield was reduced 16% and 62% for transplanted and direct-seeded rice, respectively. To minimize competition damage, farmer spend NT$ 1,8821ha (equal to NT$ 1. 36 bill ion I island-wide) on herbicides and manual weeding. Traditionally, paddy fields are cleaned to the extent free of weeds. In recent years, however, more and more rice field are appeared not well tended. Drastic change of social and economical situations has resulted in labor shortage in farm areas which makes the supplement manual weeding very costly and sometimes impractical in considering the profit. More economical and efficient measure for weed control is required in the future .