Effects of Soil Residues of Sulfosulfuron and Mesosulfuron Methyl plus Iodosulfuron Methyl Sodium on Sunflower Varieties

The effects of the residues of sulfosulfuron (75%) and mesosulfuron methyl (3%) + iodosulfuron methyl sodium (0.6%) (MM+IMS), applied at two spraying times and three application rates on two sunflower cultivars (Helianthus annus L. cv. Sanbro and cv. Aitana) seeded 12 months after treatment (MAT) were studied. Specifically, their effects on the shoot length, seed yield, and yield components, including plant length, head diameter (HD), and 1000-seed weight were investigated. Field studies were conducted over a period of two years at two locations in Ankara, Turkey. Sulfosulfuron and MM+IMS were applied post-emergence to winter wheat in 2008 at 0, 9.75, 19.5 and 39 g active ingredient (ai) ha(-1) and 0, 4.5, 9 and 18 g total ai ha(-1), respectively. Sunflower cultivars were sowed after winter wheat crop in 2009. Sunflower yield was found to be the most sensitive biological parameter to the herbicidal residue in the soil, while the 1000-seed weight was the least sensitive. Sunflower yield reduction caused by sulfosulfuron ranged from 71 to 100% and 27 to 81% in site 1 and site 2 depending on the application time, variety, and application rate, respectively. Sunflower yield at site 1 was reduced 15-76% for cv. Sanbro and 20-83% for cv. Aitana when MM+IMS treated early respectively, whereas, at site 2, the same treatment resulted in 22-36% yield reduction for cv. Sanbro and 28-43% for cv. Aitana. The yield reduction caused by the same MM+IMS rates were 49-85% for cv. Sanbro and 60-87% for cv. Aitana when MM+IMS treated late at site 1 and 49-84% for cv. Sanbro and 47-87% for cv. Aitana at site 2, respectively. Generally, the sunflower yields decreased as the dose of the chosen herbicide increased at both sites. The responses of sunflower cultivars to residues of sulfosulfuron were very similar, whereas slight differences were observed between sunflower cultivars with regard to the response to MM+IMS residue. Sulfosulfuron residues were more phytotoxic to the sunflower varieties than were MM+IMS at both sites.