Preemergent control of annual weeds in oregano (Origanum vulgare L.)

Experiments were conducted at Rio Primero, Province of Cordoba, Argentina, during 1996 and 1997, to determine efficiency of chemical control for annua l weeds in fields of oregano (Origanum vulgare L.) with different herbicide s. The assays were performed on preplanted crops grwn in loam sandy soil. T he predominant weeds were "mostacilla" (Sisymbrium irio L) and "quinoa" (Ch enopodium album L.), less prominent were "nabo" (Raphanus sativus L.), "qui mpe" (Coronopus didymus (L.) Smith), "sanguinaria" (Polygonum aviculare L.) , "ortiga mansa" (Lamium amplexicaule L.), "apio cimarron" (Apium leptophyl lum (Pers.) F.Muell.), "capiqui" (Stellaria media (L.) Villars), "estrellit a" (Bowlesia incana R. et P.) and "cardo pendiente" (Carduus nutans L.). The following herbicides and doses were used: at preplantation, trifluralin 0.96 kg i.a./ha and pendimethalin 0.99 kg/ha; at postplantation, prometryn 1.5 kg/ha, linuron 1.00 kg/ha; lenacil 0.8 kg/ha and pyridate 1.125 kg/ha. The assays were done in random in blocks with four repetitions and control plots untreated. The plots were formed by five 10 m length rows separated a t 0.70 m. The control efficiency was evaluated by recounting weed numbers a nd visual control percentage at days 21 and 49 postplantation. The phytotox ic effect on the crop was evaluated by recounting sprouted plants and estim ating damage symptoms according to a 0 to 100 % degree. The results indicated that at preplantation trifluralin and pendimethalin y ielded a reasonable weed control; trifluralin performed better. At postplan tation, prometryn was better than linuron, lenacil, and pyridate during bot h years in controlling weeds. None of the herbicides assayed significantly reduced the number of plants p roduced at transplantation; moreover, the number of oregano plants was simi lar or higher than that of the control. Neither symptoms of phytotoxicity n or yield decrease were observed.