Determination of the weed species in Çukurova onion production areas and the effects of some herbicides on the weeds and onion yield

This study was conducted to determine weed species in onion (Allium cepa L.) production areas covering Adana, Hatay and Mersin and to determine the effects of different herbicides on the weeds and onion yield between 2006 and 2007. Firstly, onion production areas of these 3 cities were determined and surveys were conducted on the way of onion production areas to determine weed species. Survey fields were chosen randomly by stopping at every 10 km. On each field, four 1 m2 quadrants were placed randomly, weed species inside the quadrants were counted and their percentage coverage areas were identified. To determine the effects of herbicides on the weeds and onion yield, experiments were done in 2 different onion fields approximately 35 km apart from each other in which one of them was in Yüzbaşı Village belonging Karataş and the other was near the Cement Factory in İncirlik. The experiments were conducted on 6 treatments and laid out in The Completely Randomized Block Design with 4 replicates.The surveys resulted with 105 weed species belonging to 30 families in onion fields. According to the weed species included, top 3 largest families were found to be Asteraceae, (17), Graminaeae (14) and Leguminosae (9). Of all these species, 57 were displayed a frequency of more than 10 per cent. Top 5 species were found as Medicago polymorpha L., Convolvulus arvensis L., Avena sterilis L., Chenopodium album L. and Sinapis arvensis L. with 84, 74, 68, 66 and 66 observation frequencies (%), respectivelly.Among the treatments used in this study, weed-free parcels gave the highest yield (16.2a kg/m2) and was followed by Oxadiazon (11.9b kg/m2), Oxyfluorfen (11.7b kg/m2), Pendimethalin (10.0c kg/m2), Tepraloxydim (9.6c kg/m2), and weedy check (9.1c kg/m2). Results, in which weed-free check caused 76.3 % increase in the onion yields when comparing with weedy checks, shows that weed control is so important for onion production.Key Words: Weed, Allium cepa L., Oxadiazon, Oxyfluorfen