Action of propanil on in vivo chlorophyll a fluorescence in Echinochloa crus‐galli and rice

Summary: When sprayed as a post‐emergent, foliar herbicide propanil destroyed Echinochloa crus‐galli (L.) with little or no visible injury to rice, confirming its selective contact action. In treated rice leaves there was, however, a temporary decrease in dry weight, pigments, proteins and photosynthetic products followed by complete recovery in 4–5 days. In both rice and E. crus‐galli , at lower concentrations propanil inhibited the electron flow in a manner similar to that of DCMU, but at higher concentrations it damaged the primary electron donor. In vivo chlorophyll a fluorescence kinetics determined at various times after spraying 1% propanil in the field confirmed progressive weed deterioration. Rice leaves showed a decreased fluorescence for a few hours but exhibited partial recovery from the effects of propanil within 6 h and total recovery within 48 h after spraying. When the leaves were infiltrated with propanil solutions there was good recovery of fluorescence in both weed and crop leaves at 0.01% while at 1% both were drastically affected. With 0.1% propanil, fluorescence in the weed leaves deteriorated progressively while the crop leaves recovered after 4 h of incubation. This suggests that the crop has also an effective endogenous detoxifying mechanism.