EARLY POST-EMERGENT CONTROL OF SMOOTH CRABGRASS AND THIN PASPALUM WITH TANK-MIXES OF VARIOUS HERBICIDES.

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1 EARLY POST-EMERGENT CONTROL OF SMOOTH CRABGRASS AND THIN PASPALUM WITH TANK-MIXES OF VARIOUS HERBICIDES. S.J. McDonald, Turfgrass Disease Solutions, LLC Abstract Smooth crabgrass (Digitaria ischaemum) and many species of paspalum are problematic grassy weeds in cool-season turfgrass. In southeastern Pennsylvania, bull or thin paspalum (Paspalum setaceum Michx.) has been observed inhibiting many low-maintenance areas in landscapes and on golf courses. In recent years, it appears that paspalum species have become more widespread and turfgrass managers are making more herbicide applications targeting their control. Sequential applications of MSMA are the current standard approach employed to control paspalum species in cool-season turfgrass species. In a pilot study conducted in 2006, it was observed that sequential applications of mesotrione at 4, 6 and 8 fluid ounces of product per acre (fl oz/a) applied-alone % v/v non-ionic surfactant caused significant injury to mature bull paspalum and smooth crabgrass. Recent reports from University of Tennessee and Virginia Tech have indicated that there are possible synergistic effects of mixing mesotrione with other herbicides. Therefore, the objective of this trial was to evaluate mesotrione applied alone and tank-mixed with selected commonly used herbicides and compare those treatments to the commercial standard (MSMA) for their ability to postemergently control smooth crabgrass and bull paspalum in a stand of fine fescue turf. Including the untreated control, there were a total of twelve treatments in this experiment. Mesotrione (8.0 fl oz/a) was applied alone and tank mixed with quinclorac (1 lb product/a), fenoxaprop (20 fl oz/a), carfentrazone (6.7 fl oz/a), sulfentrazone (4.0 fl oz/a), and fluazifop (24.0 fl oz/a). Sulfentrazone (4.0 fl oz/a) was applied alone and tan-mixed with quinclorac (1 lb product/a). Carfentrazone (6.7 fl oz/a) and quinclorac (1 lb product/a) were applied alone. Non-ionic surfactant and spray adjuvant were added as suggested by individual product labels. Initially, the site consisted of 70-85% cover by fine fescue. Treatments were initially applied on 13 June 2007 when smooth crabgrass was in the 6-7 leaf stage with 2-3 tillers and paspalum was in the 2-4 leaf stage. Paspalum germinated on 27 May 2007,

2 hence treatments were first applied 17 days after emergence. All treatments were reapplied on 1 July One week after treatment (1 WAT), plots treated with mesotrione-alone or any combination of mesotrione plus another herbicide induced significant injury to both crabgrass and paspalum (>2.0 on 0 to 5 scale). The level of injury was equal the MSMA treated plots. At 2 WAT, the highest level of treatment induced injury to crabgrass and paspalum was observed in plots treated with mesotrione-alone, mesotrione + fenoxaprop, mesotrione + fluazifop and MSMA-alone. The highest level of desirable turf (fine fescue) injury occurred in plots treated with mesotrione mixed with quinclorac and MSMA. In this trial, few distinct differences between the mesotrione-alone and the mixtures in the level of crabgrass and paspalum control were observed. Two applications of mesotrione-alone at (8.0 fl oz/a) provided a high level of control of smooth crabgrass and bull paspalum. Plots treated alone with carfentrazone-alone, sulfentrazone-alone, and quinclorac-alone had equal levels of paspalum as the untreated control throughout the entire trial. Material and Methods This trial was conducted in an out of play area behind the fifth green on the Centennial Course of Philadelphia Country Club. Turf consisted of an un-irrigated stand of fine fescue (Festuca sp). To my knowledge, this turf has not been treated with any herbicide (pre or post emergent) for the past two growing seasons. The experimental design was a randomized complete block with three replications. Individual plot size was 2.5 x 6 feet. Treatments were applied using an 8004 nozzle calibrated to deliver 1.0 gallon per 1000ft 2. Treatment application dates and rates are shown in table below. Initially, the site consisted of 70-85% cover by fine fescue. Treatments were initially applied on 13 June 2007 when smooth crabgrass was in the 6-7 leaf stage with 2-3 tillers and paspalum was in the 2-4 leaf stage. Paspalum germinated on 27 May 2007, hence treatments were first applied 17 days after emergence. All treatments were re-applied on 1 July No other weeds were observed uniformly in the trial area. Plots were rated for injury and percent coverage by the weedy grass. Injury for all species was rated on a 0 to 5 scale, where 2.5= significant herbicide induced injury, and 5=completely brown, dead tissue. Percent plot area covered by weedy grass was rated on a 0 to 100 scale, where 0= no weed coverage per plot, and 100= entire plot area covered by weed. Turfgrass quality was not rated because the 2007 summer was marked by periods of prolong drought and fine fescue exhibited signs of drought stress, even in untreated plots. Results Seven days after the first treatment (20 June), all treatments except Dismiss (Sulfentrazone)-alone, Dismiss + Drive (Quinclorac) and Drive-alone induced significant injury to the bull paspalum when compared to the untreated control (Table 1). Also on

3 20 June, significant injury to smooth crabgrass was observed. The highest level of injury to crabgrass was observed in plots treated with Tenacicty (mesotrione) + Acclaim (fenxoprop), Drive-alone, Dismiss + Drive and Tenacity + Drive. Some injury was observed to the fine fescue turf on 20 and 27 June. The highest level was observed in plots treated with Tenacity + Drive, Tenacity + Fusilade and MSMA. Overall, only Tenacity + Fusilade provided complete control of the bull or thin paspalum. This treatment, however, may be very injurious to other turfgrass species besides the fescues. It may provide a control option in naturalized areas where fescues are not under stress and the desirable species. On the final rating date, the highest level of paspalum control was observed in plots treated with Tenacity-alone (3.3%), Tenacity + Quilksivler (4.0%), Tenacity + Dismiss (8.7%), MSMA (8.0%) and Tenacity + Acclaim (9.3%). Dismiss, Quicksilver, and Drive did not provide acceptable control or suppression of the paspalum. Drive did cause slight injury in the early ratings and the drive induced injury appeared as purpling to the leaf tissue. All treatments, except Dismiss-alone, and Quicksilver-alone reduced percent plot area covered with crabgrass, when compared to the untreated control. Complete crabgrass control was provided by Tenacity + Drive, Drive-alone and Tenacity + Acclaim. Data from this trial indicate that Tenacity applied alone and in various tank mixes (with Drive, Acclaim, and Fusilade for example) offer a safe and potentially useful tool to manage crabgrass and a select species of paspalum as an alternative to MSMA. More research is needed to understand the effects of lower rates, since the high rate of Tenacity was evaluated. In the 2006 pilot study, Tenacity was applied to mature bull paspalum plants and only a slight reduction in percent plot area covered was observed. In this trial, fairly significant reductions in plot area covered were observed when Tenacity was applied to immature plants (less than 20 days since emergence). Tenacity induced injury to crabgrass at the 6 leaf stage.

4 Whitening on the leaves of the paspalum and crabgrass following application.

5 Table 1. Injury to bull paspalum and percent plot are covered by bull paspalum as influenced by various herbicide treatment, Treatment* Paspalum injury** (0-5) % plot are covered by bull paspalum x 20 June 27 June 27 June 10 July 18 August Tenacity + NIS 2.00 c y 3.43 b 6.7 cd 5.3 d 3.3 fg Tenacity + Quicksilver 2.00 c 3.40 b 8.0 cd 5.7 d 4.0 efg Tenacity + Drive + NIS 2.50 b 3.43 b 7.3 cd 1.7 d 6.0 def Tenacity + Fusilade + NIS 3.00 a 4.00 a 2.7 d 7.0 d 0.0 g Dismiss 0.00 e 0.00 d 46.7 ab 55.0 b 61.0 bc Dismiss + Drive 0.40 d 0.63 c 40.0 b 45.0 c 58.3 c Tenacity + Dismiss 2.30 bc 3.63 b 10.0 cd 5.3 d 8.7 de MSMA + NIS 2.60 b 4.00 a 12.3 c 7.0 d 8.0 def Drive + NIS 0.43 d 0.10 d 43.3 b 55.0 b 63.3 bc Quicksilver 0.00 e 0.00 d 47.7 ab 58.3 ab 65.0 ab Tenacity + Acclaim 2.53 b 3.53 b 11.3 cd 6.7 d 9.3 d Untreated 0.00 e 0.00 d 53.3 a 65.0 a 70.0 a Treatment Prob(F) * Treatments were applied on 13 June and 1 July ** Injury was rated on a 0 to 5 scale where 0= no visual injury and 5= complete dead, brown leaf tissue. x Percent plot are covered by bull paspalum was visually assessed on a 0 to 100 scale where 0= no paspalum and 100= entire plot paspalum. y Means in each column followed by different letters are significantly different (P 0.05) according to the least significant difference test.

6 Table 2. Crabgrass injury and percent plots area covered by crabgrass as influenced by various herbicide treatment, Treatment* Smooth crabgrass injury (0-5)** % plot are covered by crabgrass x 20 June 27 June 27 June 10 July 18 August Tenacity + NIS 1.00 d y 3.00 e 3.0 de 2.7 d 4.3 cd Tenacity + Quicksilver 1.53 c 3.00 e 4.3 d 2.0 d 6.0 c Tenacity + Drive + NIS 3.67 a 4.50 b 0.0 e 0.0 d 0.0 d Tenacity + Fusilade + NIS 1.20 cd 3.20 d 5.0 d 2.0 d 4.0 cd Dismiss 0.00 e 0.00 f 20.0 ab 25.0 a 31.7 a Dismiss + Drive 3.50 a 4.50 b 0.0 e 0.0 d 0.0 d Tenacity + Dismiss 1.20 cd 3.03 e 5.3 d 3.0 d 8.0 bc MSMA + NIS 2.33 b 3.53 c 10.0 c 7.0 c 11.3 b Drive + NIS 3.60 a 4.50 b 0.0 e 0.0 d 0.0 d Quicksilver 0.00 e 0.00 f 18.3 b 20.0 b 29.3 a Tenacity + Acclaim 3.77 a 5.00 a 0.0 e 0.0 d 0.0 d Untreated 0.00 e 0.00 f 23.0 a 26.0 a 30.0 a Treatment Prob(F) * Treatments were applied on 13 June and 1 July ** Injury was rated on a 0 to 5 scale where 0= no visual injury and 5= complete dead, brown leaf tissue. x Percent plot are covered by crabgrass was visually assessed on a 0 to 100 scale where 0= no crabgrass and 100= entire plot crabgrass. y Means in each column followed by different letters are significantly different (P 0.05) according to the least significant difference test.

7 Table 3. Fine fescue injury as influenced by various herbicide treatment, Treatment* Fine fescue injury** (0-5) 20 June 27 June Tenacity + NIS 0.00 d y 0.23 bc Tenacity + Quicksilver 0.00 d 0.20 bc Tenacity + Drive + NIS 1.63 b 2.67 a Tenacity + Fusilade + NIS 2.00 a 0.57 b Dismiss 0.00 d 0.00 c Dismiss + Drive 0.00 d 0.00 c Tenacity + Dismiss 0.00 d 0.00 c MSMA + NIS 1.00 c 2.67 a Drive + NIS 0.00 d 0.00 c Quicksilver 0.00 d 0.00 c Tenacity + Acclaim 0.00 d 0.23 bc Untreated 0.00 d 0.00 c Treatment Prob(F) * Treatments were applied on 13 June and 1 July ** Injury was rated on a 0 to 5 scale where 0= no visual injury and 5= complete dead, brown leaf tissue. y Means in each column followed by different letters are significantly different (P 0.05) according to the least significant difference test.