Chemical control of dandelion (Taraxacum sp.) weed in Kentucky bluegrass (Poa pratensis L.)

Dandelion with the scientific name (Taraxacum sp.) from the Asteraceae family is one of the common weeds of turfgrasses and pastures. Post-growth control of weeds in established turfgrasses is crucial and ignoring it severely damages the aesthetic aspect of turfgrass. Chemical methods are commonly used to control weeds in established turfgrass (Karimmojeni et al., 2012). The use of herbicides helps in the management of weed control in damaged turf fields along with non-chemical methods such as correct mowing height, effective irrigation, sufficient fertilization, and timely weeding. Perennial broad-leaf weeds can be selectively controlled with herbicides. U-46 Combi Fluid, Duplosan super, and Ioxynil are suitable herbicides for controlling broadleaf weeds in narrow-leaf fields.

In order to control the dandelion in Kentucky bluegrass turf, a factorial experiment was conducted based on a completely randomized design with 3 replications and 9 treatments in September 2022, at the green space of Shahrekord University. Replications included 1×1 m2 plots and the factors included two herbicides of U46-Combi Fluid and Duplosan Super and their interaction with Ioxynil. All selected plots were infested with dandelion weed. The treatments included U46-combi fluid at two levels of 1.5 and 2 L ha-1 (U1.5 and U2), Duplosan Super at two levels of 2 and 2.5 L ha-1 (D2 and D2.5), their interaction with Ioxynil herbicide at two levels (0 and 2 L ha-1) (I0 and I2), and the control (use of distilled water instead of herbicide). U-46 Combi Fluid and Duplosan Super herbicide treatments were applied at the end of September. Then, Ioxynil was applied 10 days after the first spraying. Finally, 15 days later, the effect of the treatments on the biomass characteristic of the dandelion shoots and the visual quality of turfgrass were recorded. After 50 days, the last spraying, the percentage of regrowth, herbicide control efficiency, and the biomass of turfgrass shoot were measured during the experiment. Variance analysis of data was done using SAS 9.1 statistical program and the comparison of means was conducted using LSD test (P≤0.05).

The results showed the lowest fresh and dry weight of dandelion and the highest efficiency of herbicide were found in treatments U2 + I2 and D2.5+ I2. However, these treatments had not significantly different from D2+I2 and U1.5+I2 treatments. The lowest percentage of regrowth was obtained in D2 + I2. The highest fresh weight of turfgrass was found in the control which had no significant difference with D2 + I2 and U1.5 + I2. Moreover, total chlorophyll in turfgrass leaves was improved by removing weeds. The amount of chlorophyll a, b, and total was higher in the U1.5 treatment than in other treatments. Therefore, improving the greenness of turf could be due to more light being provided to turf leaves as a result of dandelion leaf removal or positive physiological effects of 2,4-D or MCPA. There were no differences among treatments for total chlorophyll, carotenoid, visual quality, dry weight of turfgrass, and dandelion control percentage. Therefore, D2 + I2 and U1.5 + I2 can be recommended, due to the higher fresh turf weight, the good control of dandelion, and the low rate of regrowth of weed. 

Application of Duplosan Super and then Ioxynil, both with a concentration of 2.0 L ha-1 and/or U-46 Combi Fluid with a concentration of 1.5 L ha-1 and then Ioxynil with a concentration of 2.0 L ha-1 treatments are recommended due to the high weight of turfgrass, the reasonable control of dandelions, and their reduction of regrowth. In addition, leaf chlorophyll of Kentucky bluegrass treated with of U-46 Combi Fluid with a concentration of 1.5 L ha-1 was higher than in other treatments. It also had a higher turfgrass fresh weight than the 2.0 L ha-1 of U-46 Combi Fluid treatment. Duplosan Super (2.5 L ha-1) and then Ioxynil (2.0 L ha-1) treatment led to a decrease in turfgrass fresh weight compared to the same treatment without Ioxynil. In conclusion, Ioxynil concentrations at high levels did not cause visible damage, but had adverse effects on turfgrass growth, suggesting that a lower dose should be studied.