Effect of Pre- and Post-Emergence Herbicides on Weed Control and Yield in Sunflower (Helianthus annuus L.)

Weeds are a major cause of yield and quality loss in sunflower (Helianthus annuus L.) crops. Therefore, weed control is important in sunflower production. In this context, the study was conducted in 2023 to determine the effectiveness of pre-emergence and post-emergence herbicides with different modes of action on weed population, dry weight of weeds and sunflower yield and yield components in sunflower. Four herbicides with different modes of action, three pre-emergence (aclonifen (A), pendimethalin (P), linuron (L) and one post-emergence (quizalofop-p-ethyl) (Q) and combinations of these herbicides were used in the study. To determine the effects of herbicides on weed populations and species, four different assessments were conducted at regular intervals. As a result of the study, a total of 10 weed species belonging to 5 families were detected in the trial area. The weed species with the highest density were Sorghum halepense (L.) Pers., Xanthium strumarium L., Convolvulus arvensis L. and Chenopodium album L. The study found that the effects of herbicides on weed populations and species varied. In the study, the highest rates of weed control were achieved in plots where both pre-emergence and post-emergence herbicides were used together. The highest weed control rate was observed in plots P+Q (96.66%). The highest effect on weed dry weight was obtained in plot L+Q with a rate of 89.63%. The highest weed dry weight was recorded in the weedy control plots. In the study, the highest yield (287.53 kg da-1) was obtained in the weed-free (hoe) control plot. Yield increases of 18% to 45% can be achieved by controlling weeds in sunflowers. As a result, herbicide efficacy on weed population and dry weight of weeds increased when herbicides were used in combination. Some herbicides have been shown to increase yields when used alone. However, it is important to use herbicides in combination to control more weed populations and prevent a potential resistance problem.