EFFECTS OF CHLOROACETAMIDES AND PHYTOSYNTHESIS-INHIBITING HERBICIDES ON GROWTH AND PHOTOSYNTHESIS IN SUNFLOWER (HELIANTHUS-ANNUUS L) AND AMARANTHUS-HYBRIDUS L

The effects of the chloroacetamide herbicides acetochlor, alachlor and propachlor and the photosynthesis-inhibiting herbicides linuron, prom etryn and terbutryn on sunflower (Helianthus annuus L.) and atrazine-s ensitive and -resistant Amaranthus hybridus L. biotypes were investiga ted under laboratory conditions. Sunflower tolerated all three chloroa cetamides in pre-emergence applications of 1.5-5.0 kg a.i. ha-1 in gro wth assays. Sunflower also survived doses of 0.5-1.0 kg a.i. ha-1 of l inuron, prometryn and terbutryn, although growth reduction and chloros is of treated plants was observed. These three herbicides inhibited ph otosynthetic electron transport in in vitro Hill reaction and fluoresc ence assays and, with terbutryn, photosynthesis recovered upon transfe r of the leaves from herbicide solutions to water. The practical signi ficance of these results for the control of weeds in sunflower cultiva tion in Spain are discussed.