Efficiency of pendimethalin, ioxynil, and accase inhibitors in controlling weeds in direct seeding onion

This study evaluates whether the initial application of pendimethalin can increase the efficiency of ioxynil and ACCase inhibitor treatments in controlling weeds in direct seeding onion. The experiment was carried out in a commercial field in Ituporanga city, Santa Catarina State, Brazil. The onion cultivar Bola Precoce was used. The experimental design was in randomized blocks, in a factorial scheme (2 x 3) + 1, with four replications. Treat­ments consisted of pendimethalin application in the initial stage (0 or 600 g ha -1 ), three treatments based on ioxynil and ACCase inhibitors, sprayed at postemergence (ioxynil + clethodim (formulated as Select ® ); ioxynil + fluazifop; and ioxynil + clethodim (formulated as Poquer ® )), and a weeded control. Pendimethalin was sprayed immediately after onion crop establishment, and postemergence treatments were sprayed when the onion had 3 and 4 leaves (two sequential applications). The following were evaluated: control of Lolium multiflorum , Corono­pus didymus , and Galinsoga parviflora , plant stand, bulb diameter, bulb weight, and total bulb yield. All treatments reached 100% control of L. multiflorum . All treatments were ineffective in controlling C. didymus and G. parviflora ; however, the control of these weeds increased after pendimethalin application. The chemical treatments tested did not negatively influence any of the studied onion crop variables. There was a significant difference only for pendimethalin application in the initial stage, which significantly favored the variables under study. Pendimethalin application in the initial onion stage improved weed control and helped in maintaining bulb yield in direct seeding onion.