Summary: This study showed that Dismiss and Echelon provided excellent preemergence yellow nutsedge control, but these herbicides should not be used in a tall fescue seedbed. Tenacity applied twice at 0.1 87 lb/A provided a level of yellow nutsedge control similar to Dismiss and Echelon. However, Tenacity works slowly and must be applied twice to achieve the same yellow nutsedge control levels as Dismiss or Echelon applied once. Regardless, Tenacity was shown to be safe and can be used effectively in spring seeded tall fescue for preemergence and early postemergence yellow nutsedge control. However, Tenacity is only labeled for golf courses while Dismiss and echelon are labeled for home lawns.
Procedures: The perennial ryegrass (Lolium perenne) study site was treated with glyphosate on 5 April 2007, and diskseeded with ‘Cochise III’ tall fescue (Festuca arundinacea) on 10 April 2007, using 6.0 lb seed/1000ft2. Tenacity (mesotrione), Dismiss (sulfentrazone) and Echelon (sulfentrazone plus prodiamine) were applied in 50 GPA using a CO2 pressurized (35 psi) backpack sprayer equipped with an 8004E nozzle. Tenacity treatments were applied once or sequentially. Sequential applications of Tenacity were tank-mixed with 0.25% v/v with X-77 NIS. Dismiss was applied once and sequentially and Echelon was applied once at two rates. All treatments initially were applied on 20 April 2007, before yellow nutsedge (Cyperus esculentus; YNS) and tall fescue plants had emerged. Yellow nutsedge plants began emerging from tubers about one week (i.e., 28 April) after the herbicides were initially applied. A sequential application of selected treatments was made on 21 May. The site was mowed 24 to 48 hrs prior to treatment and there was good soil moisture on all dates that herbicides were applied. The site was treated with fenoxaprop (0.09 lb ai/A) on 1 June 2007 to control smooth crabgrass (Digitaria ischaemum) postemergence. Urea was applied 18 May 2007 to provide 1.0 lb N/1000ft2. Turf was mowed twice weekly to a height of 2.5 inches. The site was irrigated frequently to present drought stress. Soil was a Keyport silt loam with a pH of 6.0 and 2.6% OM. Plots were 5 ft x 5 ft and there were arranged in a randomized complete block with four replications. Yellow nutsedge and tall fescue cover were assessed visually on a linear 0 to 100% scale where 0 = no YNS or tall fescue and 100 = entire plot area covered with YNS or tall fescue. Data were subjected to ANOVA and significantly different means were separated by Fisher’s LSD at P £0.05.
Results: The herbicides were applied preemergence to the appearance both YNS and tall fescue. Both seedlings of tall fescue and shoots of YNS emanating from tubers began emerging in late April and early May. In plots treated with Tenacity, YNS shoots emerged and turned white and many plants died over a period of weeks. In plots treated with Dismiss and Echelon, emerging shoots of YNS were not observed. Evidently, the emerging shoots were rapidly killed at or below the soil surface by the aforementioned herbicides, since the herbicides had no direct contact with tubers. Initially, it was difficult to differentiate tall fescue and YNS and percent area green cover was initially rated, but data are not shown. By 31 May, it was easy to differentiate the yellow leaves of YNS from the dark green tall fescue leaves. On 31 May, 10 days had passed since sequential applications were made and all treatments had reduced YNS cover ratings than plots treated with Tenacity on 31 May. By 20 June, plots treated with Tenacity at 0.197 + 0.187 lb/A had YNS cover levels equivalent to plots treated with Dismiss or Echelon. Similar results were observed on 1 August, but at that time plots treated with Tenacity (0.125 + 0.125 and 0.187 lb/A) had YNS levels generally equivalent to Dismiss and Echelon-treated plots. Plots treated with Dismiss (0.125 and 0.125 lb/A), however, were almost free of YNS cover on 1 August.
While Dismiss and Echelon provided outstanding preemergence YNS control, they also adversely affected the emergence of tall fescue. Echelon was more injurious than Dismiss. Over the course of time between 31 May and 1 August, the low levels of surviving tall fescue plants in Dismiss and Echelon-treated plots began too increase in size by tillering. While tall fescue cover ratings were 1.6 to 12.5% in Dismiss- treated plots on 31 May, cover ratings increased to 47.5 to 69.5% by 1 August and were greater than was observed in untreated plots. These tall fescue levels however provided a poor to fair quality turf throughout the summer. Echelon was even more injurious and tall fescue cover ratings were only 8.5 to 18.5% by 1 August. Conversely, Tenacity had no visual adverse effects on tall fescue seedling emergence or development. Plots treated with Tenacity twice at the high rate (i.e., 0.187 lb/A) achieved about 85% tall fescue cover by 8 June and retained this cover level the entire summer. Lower levels of tall fescue cover were observed in plots treated with Tenacity once at 0.25 1b/A or sequentially at 0.125 + 0.125 lb/A. The higher levels of YNS provide significant competition to the tall fescue in plots treated with the lower rates of Tenacity. Indeed, untreated plots had only 11% tall fescue cover by 1 August due to YNS competition and possibly allelopathic effects. There were no significant tall fescue cover differences among Tenacity treatments on 1 August, but the high rate applied sequentially made for a superior turf more rapidly.
This study showed that Dismiss and Echelon provided excellent preemergence YNS control, but these herbicides should not be used in a tall fescue seedbed. Tenacity applied twice at 0.1 87 lb/A provided a level of YNS control similar to Dismiss and Echelon. However, Tenacity works slowly and must be applied twice to achieve the same YNS control levels as Dismiss or Echelon applied once. Regardless, Tenacity was shown to be safe and can be used effectively in spring seeded tall fescue for preemergence and early postemergence YNS control.
