Abstract
Successful weed control before seeding is necessary for proper turfgrass establishment. However, herbicide labels differ in the time required between application and seeding. The objective of this research was to determine the influence of four postemergence broadleaf combination herbicides on tall fescue (Festuca arundinacea) cover, normalized difference vegetation index (NDVI), and canopy height when seeded 0, 3, 7, and 14 days after herbicide application. Herbicide treatments included the following: 1) a nontreated control; 2) 0.03 lb/acre carfentrazone-ethyl + 0.09 lb/acre methylchlorophenoxypropionic acid (MCPP) + 1.44 lb/acre 2,4-dichlorophenoxyacetic acid (2,4-D) + 0.30 lb/acre dicamba; 3) 0.20 lb/acre fluroxypyr + 0.01 lb/acre halauxifen-methyl + 1.44 lb/acre 2,4-D choline; 4) 0.20 lb/acre triclopyr + 0.003 lb/acre pyraflufen-ethyl + 1.72 lb/acre 2,4-D + 0.14/acre dicamba; and 5) 0.04 lb/acre penoxsulam + 0.04 lb/acre sulfentrazone + 0.40 lb/acre 2,4-D + 0.11 lb/acre dicamba. Penoxsulam + sulfentrazone + 2,4-D + dicamba reduced tall fescue cover, NDVI, and canopy height compared with the nontreated. This research demonstrates seeding between 0 to 14 days after an application of carfentrazone-ethyl + MCPP + 2,4-D + dicamba, fluroxypyr + halauxifen-methyl + 2,4-D choline, or triclopyr + pyraflufen-ethyl + 2,4-D + dicamba will result in successful tall fescue establishment under the conditions evaluated in these experiments.
Effective weed control before seeding is essential for proper turfgrass establishment because competition from weeds can cause sward establishment to fail (Dunn and Diesburg 2004; Patton et al. 2009). Herbicides are a vital component to weed management in turfgrass; however, limited research exists on weed control at the time of seeding despite the common practice of reseeding immediately after herbicide application (McElroy and Martins 2013; Wagner and Nelson 2014).
Commonly used products for postemergence broadleaf weed control, such as 2,4-dichlorophenoxyacetic acid (2,4-D), dicamba, triclopyr, or methylchlorophenoxypropionic acid (MCPP), are only recommended for application after turfgrass seedlings have emerged and tillered (Askew and Hipkins 2005; Willis et al. 2006). Most herbicide labels recommend waiting for a defined period of time before seeding; applying herbicides before seeding can affect germination and growth of seedlings (Johnston et al. 2016; Kaminski et al. 2004; McElroy and Breeden 2007).
In Georgia, Tennessee, and Texas, application of the postemergence broadleaf herbicides aminocyclopyrachlor or 2,4-D + dicamba + MCPP, at different rates at 0, 2, 4, or 6 weeks before seeding perennial ryegrass (Lolium perenne) and tall fescue (Festuca arundinacea) resulted in similar establishment compared with nontreated turfgrass and suggested no seeding delay was required after application (Workman et al. 2012). Another study, by Li et al. (2015), found that combination products used for broadleaf weed control, such as sulfentrazone + quinclorac, carfentrazone-ethyl + quinclorac, and sulfentrazone + prodiamine, were safe to apply at the time of buffalograss (Buchloe dactyloides) seeding and effectively minimized weed pressure.
The introduction of new combination products raises concerns regarding the delay in seeding required after application. Herbicides with multiple active ingredients from different chemical families could increase efficacy, but hinder the establishment of newly seeded turfgrass. Information is needed on postemergence broadleaf combination herbicide products and their effect on tall fescue establishment. Therefore, the objective of this research was to determine the influence of combination herbicide products used for postemergence control of broadleaf weeds on the establishment of tall fescue seeded between 0 and 14 d after application.
Materials and methods
Experimental layout
Field experiments were conducted at the Olathe Horticulture Research and Extension Center in Olathe, KS, USA (lat. 39.48°N, long. 95.66°W) and at the Rocky Ford Turfgrass Research Center in Manhattan, KS, USA (lat. 39.13°N, long. 96.36°W). The experimental design was a two-way factorial, randomized complete block with four replications of plots measuring 4 × 4 ft. Main factors included four seeding intervals (0, 3, 7, and 14 d after herbicide application), and five herbicide treatments including a nontreated control (Table 1) for a total of 20 individual treatments.
Herbicides evaluated for effects on tall fescue (Festuca arundinacea) seeded after application at the Olathe Horticulture Research and Extension Center in Olathe, KS, USA, and the Rocky Ford Turfgrass Research Center in Manhattan, KS. in 2020. Tall fescue was seeded 0, 3, 7, and 14 d after herbicide treatment.
Soil at the Olathe site was an Oska-Martin silty clay loam (fine, smectitic, mesic Vertic Argiudolls) with 5.5 pH. Before study initiation, sequential applications of 2.1 lb/acre a.e. glyphosate (Glyphomate 41; PBI-Gordon Corp., Shawnee, KS, USA) were made on 29 Jul and 12 Aug 2020 to control existing zoysiagrass (Zoysia japonica) vegetation. Following the sequential glyphosate applications, the site was verticut in three directions with a power rake (Billy Goat Industries Inc., Lee’s Summit, MO, USA) with 2.0-inch blade spacing on a No. 4 setting. Plots were raked to remove the material that had been verticut before herbicide application. Herbicide treatments were applied on 24 Aug 2020 in Olathe using a carbon dioxide (CO2)-pressurized, hand-held spray boom (R&D Sprayers, Opelousas, LA, USA) equipped with four flat-fan nozzles (8003; TeeJet Technologies, Springfield, IL, USA) on 25-cm spacing calibrated to deliver 43 gal/acre. Before seeding plots within each respective interval, a three-tine rotary cultivator (2917000 Steel Tine Garden Cultivator; The Ames Companies, Camp Hill, PA, USA) was used to lightly disturb the top 1 inch of the soil surface by making nine passes in two opposite directions in each plot. A starter fertilizer (14N–8.7P–3.3K) was applied to deliver 1 lb/1000 ft2 phosphorus. Tall fescue [Heat WaveTM; Grass Pad, Olathe, KS, USA (8.3% ‘Rendition’, 28.2% ‘Covenant II’, 26.8% ‘Falcon IV’, and 16% ‘Renegade DT’)] was seeded at 10 lb/1000 ft2 pure live seed. Seeding intervals consisted of 0 d (24 Aug 2020), 3 d (27 Aug 2020), 7 d (31 Aug 2020), and 14 d (7 Sep 2020) after herbicide treatment. Both the granular fertilizer and seed were spread independently using a shaker bottle in multiple directions. Irrigation was withheld until 24 h after herbicide application. Following the 24-h period, supplemental irrigation ran once daily to keep the canopy moist. Plots were not mown throughout the duration of the study. During the experimental period (24 Aug to 19 Oct), average temperatures were as follows: 77.5 °F maximum air, 53.3 °F minimum air, 64.2 °F minimum soil at 2-inch depth. Rainfall total in Olathe was 122 mm.
Soil at the Manhattan site was a Chase silty loam (fine, smectitic, mesic Aquertic Argiudolls) with 6.8 pH. Before study initiation, sequential applications of 2.1 lb/acre a.e. glyphosate (Glyphomate 41) on 5 Aug and 26 Aug 2020 to control existing tall fescue vegetation. Following glyphosate applications, the study site was scalped with a reel mower to 0.5 inch in two directions with clippings collected. Herbicide treatments were applied on 2 Sep 2020 in Manhattan using a CO2-pressurized, hand-held spray boom (R&D Sprayers) equipped with four flat-fan nozzles (8003) on 25-cm spacing calibrated to deliver 43 gal/acre. Seeding intervals consisted of 0 d (2 Sep 2020), 3 d (5 Sep 2020), 7 d (9 Sep 2020), and 14 d (16 Sep 2020) after herbicide treatment (DAT). Plot size, soil preparation, fertilization, seeding, irrigation, and mowing in Manhattan were the same as described in Olathe. In Manhattan during the experimental period (2 Sep to 28 Oct), average temperatures were as follows: 70.9 °F maximum air, 46.9 °F minimum air, 59.5 °F minimum soil at 2-inch depth. Total rainfall in Manhattan was 60 mm. Both locations were within the same latitude; however, soil type, and pH at study initiation, as well as average temperatures, and rainfall totals differed between the locations. This justified duplication of the experiment at these two sites.
Measurements and statistical analysis
At both locations, tall fescue cover was visually rated weekly using a scale of 0% to 100% cover (0% = no visible cover; 100% = full cover of experimental plot). The NDVI was determined using a meter (FieldScout CM 1000 NDVI Meter; Spectrum Technologies, Aurora, IL, USA), and values were recorded at 28, 42, and 56 d after seeding. The NDVI values range from −1 to 1, with higher values indicating greater plant health; these values were recorded by taking the average of three randomly selected areas within each experimental plot. Canopy height (inches) was measured 42 DAT by placing a ruler perpendicular to the soil surface in three random areas of each plot and visually observing height against the ruler; means were recorded. All data for each of the ratings were subjected to analysis of variance statistical software (SAS version 9.4; SAS Institute Inc., Cary, NC, USA) using the GLIMMIX procedure to determine those factors that were significant (P ≤ 0.05) and means were separated according to Tukey’s honestly significant difference test. Data were initially combined to see if location by treatment interactions were significant. For tall fescue cover and canopy height data, a significant herbicide treatment by location interaction was found, and thus data were analyzed separately by location. Location was not significant for NDVI on all three rating dates, so values are pooled across locations by herbicide treatment. The herbicide treatment main effect was significant for tall fescue cover, NDVI, and canopy height data, but no significant interaction between seeding interval and herbicide treatment was observed. Data are presented in tables from dates that are reflective of treatment differences across the experimental period.
Results and discussion
At the Olathe site, no herbicide treatment reduced tall fescue cover compared with the nontreated at 35 and 56 DAT; all had ≥ 67% cover and ≥ 90% cover, respectively (Table 2). At the Manhattan site, tall fescue visual cover was reduced in penoxsulam + sulfentrazone + 2,4-D + dicamba-treated plots compared with nontreated; penoxsulam + sulfentrazone + 2,4-D + dicamba-treated plots reached 88% cover at 56 DAT while the nontreated averaged 95% cover 56 DAT. No other herbicide treatment reduced cover compared with the nontreated; all had ≥ 94% visual cover.
Main effect of herbicides on tall fescue (Festuca arundinacea) cover 5 and 8 weeks after seeding 0 to 14 d after treatment (DAT) in Olathe and Manhattan, KS, USA. Means are averages over seeding intervals (n = 16).
At 28, 42, and 56 DAT, NDVI values showed no significant difference in live green vegetation at either site for all herbicide treatments compared with nontreated except for penoxsulam + sulfentrazone + 2,4-D + dicamba-treated plots (Table 3). However, all treatments at 56 DAT had a mean NDVI value above 0.80.
Main effect of herbicides on tall fescue (Festuca arundinacea) normalized difference vegetation index (NDVI) 4, 6, and 8 weeks after seeding 0 to 14 d after treatment (DAT) in Olathe and Manhattan, KS, USA. Means are averages over seeding intervals and location (n = 32).
Canopy height was significantly lower in penoxsulam + sulfentrazone + 2,4-D + dicamba-treated plots (2.6 and 2.7 inches at Olathe and Manhattan, respectively) when compared with nontreated (3.3 and 5.0 inches at Olathe and Manhattan, respectively; Table 4). No other herbicide treatment reduced canopy height compared with the nontreated at either site.
Main effect of herbicides on tall fescue (Festuca arundinacea) seedling canopy height 6 weeks after seeding 0 to 14 d after treatment (DAT) in Olathe and Manhattan, KS. Means are averages over seeding intervals (n = 16).
Tall fescue seeded into penoxsulam + sulfentrazone + 2,4-D + dicamba-treated plots was consistently lower in cover, canopy height, and NDVI ratings compared with the nontreated. Penoxsulam is an acetolactate synthase-inhibiting herbicide with early postemergence activity on broadleaf weeds and is often combined with other herbicides for a broader spectrum of control with a single application (Brosnan and Breeden 2019). Sulfentrazone, a protoporphyrinogen oxidase inhibitor, is in the same chemical class as carfentrazone-ethyl and is absorbed through the roots and shoots (Senseman 2007). However, sulfentrazone applied either at the time of seeding buffalograss and at emergence effectively minimized weed pressure while leaving buffalograss establishment unharmed (Li et al. 2015). Our results indicate that a reseeding interval of 14 d or more after the application may be necessary for optimal tall fescue seedling establishment.
Seeding between 0 and 14 d after an application of carfentrazone-ethyl + MCPP + 2,4-D + dicamba, fluroxypyr + halauxifen-methyl + 2,4-D, or triclopyr + pyraflufen-ethyl + 2,4-D + dicamba had little or no effect on tall fescue growth under the conditions evaluated in these experiments. Turfgrass managers who unknowingly seed into areas treated with these combination products will likely observe successful establishment of tall fescue when seeded in the fall, when soil temperatures are ideal for cool-season turfgrass growth under adequate irrigation. It should be noted that rooting was not evaluated in this experiment, and some postemergence herbicides can inhibit rooting of seedlings after application. In general, herbicide manufacturers could consider altering product label reseeding intervals, using results reported herein as guidelines. Herbicide labels are commonly developed with a safety factor of two or three times the recommended application rate. Future research should investigate seedling safety when higher herbicide rates are applied.
Units
References cited
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