Influence of glyphosate (Roundup Ultra®) rate and time of application on weed control and performance of DP5415RR cotton in Israel: Field and laboratory experiments

Field and laboratory trials were conducted at four locations in Israel in 1998 and 1999 to evaluate the performance of glyphosate-resistant cotton (Roundup Ready, cv. DP5415RR). Cotton plants treated postemergency (POST) with glyphosate at various rates and growth stages did not show any visual injury. Late application of glyphosate (8- to 10- leaf stage) resulted in deformed cotton flowers particularly in the first blooming flush. Anthers were degenerated and released very little pollen. Final plant mappings have shown that the late application of glyphosate (1.44 kg/ha) resulted in a significant increase in the number of bolls per plant and a concomitant decrease in boll weight of the bottom fruiting branches. In spite of the observed detrimental effects, no yield reduction was recorded. Excellent weed control was observed in all experiments at all herbicide rates and timings tested. However, control of troublesome weeds like purple nutsedge (Cyperus rotundus) was improved when late and high application rates were used. Cross-pollination between 'DP5415RR' and a neighboring local cultivar 'Sivon' was evaluated by testing the response to glyphosate of the progeny collected from 'Sivon' plants grown at different distances. Less than 10% gene transfer was detected at 1 m distance and less than 0.5% at 35 m from the RR plot.