Response of Azolla to Some Pre-emergence Herbicides and Effect of AzolIa Covering on Weeds

Abstract

Azolla was killed by the following 9 paddy herbicides, Machete, Machete+K223, Machete+Mo338, Machete+X-52, Modown, Ronstar , Saturn, TOK and X-52 at the recommended rates in pot tests where free water was maintained at 2 cm height. When free water was increased to 5 cm height, the herbicides were still detrimental to the growth of azolla. The toxicity of herbicides was still observed, even when azolla was inoculated at the sixth day after herbicide application.Most of the azolla plants were killed by Modown and TOK at the concentration of 0.1 ppm(ai). However, the survived plants could still propagate and then cover the water surface within 30 days after application. All azolla plants were killed completely by Machete and Saturn at the concentration of 1 ppm.In comparison with non-azolla inoculated control in green house, 80 and 90 per cent of the weeds in soils sampled from the 1st and 2nd rice crops, respectively, were inhibited by the azolla covering on the water surface. Weed reducing effects were also observed in the dual culture of azolla and rice. 水深2公分情形下，下列9種水田殺草劑即丁基拉草、丁拉克草、丁拉滅草、丁拉甲護谷、魔丹（必芬諾）、樂滅草、掃丹及甲氧基護谷，在推薦用量都會殺死滿江紅。水深增至5公分時各殺草劑對滿江紅毒害仍大。殺草劑施用第六天後，再接種滿江紅亦無法避免殺草劑之危害。大部份滿江紅在0.1ppm(ai)之魔丹及甲氧基護谷處理下，即被殺死，但少數存活者在一個月內可以快速增殖而覆蓋整個水面。在1ppm(ai)之Machete及Saturn處理下，所有滿江紅都被殺死。溫室中，與無滿江紅覆蓋者相比較，覆蓋滿江紅者可以減少80%以上及90%以上之一期作與二期作水田土內之雜草數，田間滿江紅與水稻共作時亦具明顯的防治雜草效果。