LAUSR

Chlorophyll fluorescence analysis is a simple and rapid method for detecting herbicide effects after a short time following their application in photosynthetic apparatus in plants. Chlorophyll fluorescence measurements were carried out against two broad of weeds to describe how the Kautsky curve and its parameters were affected by herbicides. Desmedipham + phenmedipham + ethofumesate changed the chlorophyll fluorescence induction curve at all time intervals except four hours after spring (HAS) in Amaranthus retroflexus L. and at all doses of Portulaca oleracea L. 4 HAS. In contrast, chlorophyll fluorescence inhibition was evident by chloridazon at doses of 650 and 325 g a.i. ha -1 in P. oleracea and A. retroflexus respectively, for all time intervals. Furthermore, chlorophyll fluorescence decays only occurred by clopyralid in A. retroflexus at the highest dose. A biomass effective dose (ED 50 and/or ED 90 ) based on log-logistic dose-response curves for A. retroflexus were considerably higher than that of P. oleracea . The maximum quantum efficiency (F V /F m ) was stable, whereas the relative changes at the J step (F vj ) and area (the area between the Kautsky curve and the maximum fluorescence (F m )) was more sensitive to all three herbicides. There was a relatively good correlation between fluorescence parameters taken 24 hours after the spraying and the dry matter taken three weeks later, for both species under study.