Cyperus serotinus

The primary mode of action of bentazon is the inhibition of photosynthetic CO2-fixation by the plants (Mine and Matsunaka, 1973, 1975). A marked inhibition of C02-fixation develops rapidly both in resistant rice and in sensitive Cyperus serotinus after treatment with bentazon, but while tolerant rice recovers almost completely in 5 days, sensitive Cyperus serotinus does not recover. 

Searching into the cause of the selectivity of bentazon. Mine et al. (1973, 1975) investigated the adsorption and translocation of the herbicide in sensitive Cyperus serotinus and in resistant rice. There is no substantial difference in either the absorption or in the translocation of the herbicide in the two kinds of plants. However, in rice 80% of the bentazon absorbed is metabolised in 24 hours and 85% is converted in 7 days to a water-soluble metabolite. The major metabolite formed in rice is 6-isopropyl-2,l,3-benzothiadiazinon-(4)-2,2-dioxide O- -glucopyra-noside. Only 5% of unchanged bentazon can be detected in rice, while in Cyperus serotinus 50-75% of the bentazon is present in unchanged form after 7 days. 

Komal et (Ref. 53) found gc-ms evidence of the sesquiterpenes 6 sellnene (54), methyl farnesate, farnesyl acetate (55), and farnesol (56) present In an Inhibitory fraction Isolated from water nutgrass (Cyperus serotinus ). This fraction at 300 ppm Inhibited lettuce germination and also Inhibited growth of lettuce and rice seedlings as well as nutgrass Itself. The authors conclude that the sesquiterpenes are responsible for the observed allelopathlc effects. 

K. Komal, Y. Suglwaka and S. Sato, "Plant-growth Retardant of Extracts Obtained from Water Nutgrass (Cyperus serotinus Rottb.)", Klnkl Dalgaku Nogakubu Klyo, 1981, (14), 57-65. 

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