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RESEARCH PRODUCT

Studies on the Effect of Cell Division-inhibiting Herbicides on Unialgal and Mixed Algal Cultures

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The effect of two cell division inhibiting herbicides on unialgal and mixed algal cultures was studied in laboratory tests. The herbicides studied were trifluralin (analytical grade) and the active ingredient as well as the preparation (80 % a.i.) of diphenamid. The three green algal species used were Selenastrum capricornutum PRINTZ, Scenedesmus quadricauda (TURP.) BREB., Oocystis parva W. et G. S. WEST. The response of algae to herbicides was determined by cell counting, and measured by turbidity (750 nm) and the 02-production of some of the treated cultures. The EC50-value (96 h) of trifluralin to Selenastrum capricornutum was 3.3 mg/l. There were differences in the sensitivity of the three algal strains to the diphenamid; the EC50-values to Selenastrum, Scenedesmus and Oocystis were 16.7, 10.1 and 6.3 mg/l, respectively. The lag phase observed in the growth of the treated cultures caused by diphenamid was verified by O2-measurements. The preparation of diphenamid was not as effective as the active ingredient. In mixed cultures the ratio between two different algal strains depended both on the concentration of the diphenamid and the sensitivity of the two strains.