Abstract
Introduction
Adding an adjuvant facilitates the uptake of herbicides through the aerial parts of plants and reduces the selective state of the herbicide. If the amount of adjuvants is more than the amount needed to moisturize the surface of the plants, the penetration of herbicides will increase. The experiment reported here was conducted to determine the best additives on increasing the effectiveness of herbicides in controlling wheat weeds.
 
Materials and Methods
The experiment was conducted in a randomized complete block design with three replications in a farm in Fasa (28° 56' N, 53°38′E) during 2017-2018. The factors consisted of herbicides in four levels of Mesosulfuron+ Iodosulfuron+ Diflufenican (Othello), Clodinafop Propargyl (Topik)+ Tribenuron–Methyl (Granstar), Sulfosulfuron+ Metsulfuron Methyl (Total) and Sulfosulfuron (Apirus) in recommended doses and type of additives in 4 levels, Ammonium Sulfate 2%, soybean oil 1.25%, cleaner liquid as surfactant Anionic 0.5% and without additive as control. Wheat seeds of Chamran cultivar with vigour of 98% at rate of 150 kg.ha^-1 were planted in rows of 10 cm. The dimensions of each experimental plot were 2´4 m. Herbicide application time was also in the wheat tillering and 2-4 leaf weeding stages. The experimental sprayer was used with a manual pump, having a nozzle with a spray angle of 30 degrees, a constant pressure of 50 psi and a spray height of 20 inches (50 cm) calibrated for spraying. Characteristics such as dry weight of narrow weeds included wild oat (dominant weed) along with canary grass and Ryegrass, broad-leaf weeds including charlock mustard (dominant weed) along with fumitories were measured. Number of spikes per square meter, number of seeds per spike, 1000 grain weight, biological yield, grain yield and wheat harvest index were measured too.
 
Results and Discussion
The results showed that among the additives used, 2% Ammonium Sulfate had the greatest effect on reducing the dry weight of weeds, narrow-leaf (34.05%) and broad-leaf (31.57%) weeds. The herbicides Othello, Topik+ Granstar and Total had performed well on wheat grain yield, but did not result in significant differences. The combination of additives with herbicides compared to no adjuvant control increased grain yield (on average, 607.73 kg.ha^-1). Finally, Othello herbicide was identified as the best treatment for this test due to its consumption of 2% Ammonium Sulfate additive. The effect of herbicides application of Othello, Topik+ Granstar and Total on grain yield can be due to their effect on decrease of weed dry weight. The results indicate that Ammonium Sulfate 2% increased the uptake of herbicides ,accordingly it increases the effectiveness of herbicides in weed control and grain yield increase.
 
Conclusion
Combining each of the adjuvants with herbicides increased the grain yield of wheat. Among the additives, Ammonium Sulfate was the most effective. 2% Ammonium Sulfate with an average yield of 6203 kg.ha^‑1 showed the highest effect. The results of the means revealed that the herbicides Apirus, Othello and Total had the greatest effect on increasing wheat grain.