Using florescence induction curve on the control of Amaranthus retroflexus and Solanum nigrum

In order to determine how exposure affects the Kautsky curve and its parameters, two dose-response experiments were carried out for chlorophyll fluorescence measuring.The treatments involved desmedipham phenmedipham ethofumesate, chloridazon and clopyralid on redroot pigweed (Amaranthusretroflexus L.)andblack nightshade (Solanum nigrum L.) at the research glasshouse of Agricultural Faculty of Ferdowsi University of Mashhad, Iran, during 2013. On the base of observation evaluation results, Solanum nigrum showed the highest susceptibility to desmedipham phenmedipham ethofumesate, so that application of 308.25 g a.i. ha-1 of herbicide resulted in 100 percent control, 21 days after treatment. The results of chlorophyll fluorescence showed that the mentioned herbicides effect was more in S. nigrum than in A.retroflexus.As Kautsky curve were affected and changed in an almost horizontal lines by desmedipham phenmedipham ethofumesate in both weed species at 4 HAS at doses of 51.38 mg a.i. ha-1,whereasthefluorescence rate was reduced in S. nigrum and A.retroflexusat doses of 81.25 and 325 mg a.i. ha-1 respectively bychloridazon. According to visual observations, chloridazon had significant effect on the control of Solanum nigrum and Amaranthus retroflexus, and clopyralid controlled Solanum nigrum better than Amaranthus retroflexus. Thefluorescence rate was decreased at doses of 240 mg a.i. ha-1 inA. retroflexus, 180 and 240 mg a.i. ha-1 for S. nigrum, and therefore, Kautsky curve was changed entirely. Among fluorescence parameters, Fvj andArea parameters were severely reduced.