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J. Scott McElroy, James D. McCurdy, and Michael L. Flessner

Centipedegrass (Eremochloa ophiuroides) is a low-maintenance, warm-season grass common throughout the southern United States. Slow establishment and growth rate of seeded centipedegrass often allows for increased weed competition, yet weed control options are limited. Tank-mixing simazine with mesotrione has been reported to improve weed control because of synergistic modes of action. A 2-year field trial was conducted to evaluate centipedegrass response to mesotrione and simazine applications applied 2 weeks after emergence. Mesotrione (0.25 lb/acre) did not reduce centipedegrass cover at any rating when applied alone. All rates of simazine, alone and tank-mixed with mesotrione, resulted in decreased centipedegrass cover 7 days after treatment (DAT). However, simazine alone at 0.25 lb/acre did not reduce turf cover 14, 28, and 49 DAT, and simazine at 0.25 lb/acre tank-mixed with mesotrione at 0.25 lb/acre did not reduce turf cover 28 and 49 DAT. Results indicate that newly established centipedegrass is vulnerable to cover reduction because of simazine and simazine plus mesotrione tank-mixture. Mesotrione and mesotrione tank-mixed with low rates of simazine is a viable option for newly seeded centipedegrass weed control; however, turf cover may be delayed.

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Donald T. Jensen, Schuyler D. Seeley, James Frisby, and Greg McCurdy

A Latin Square design was used to determine effects of undertree irrigation on orchard temperatures during freezes. Plots (40 × 40 m) in a tart cherry orchard included 72 trees. Water was applied at 0, 125, 250 and 380 (± 5%) liters/min. Four meter towers held shielded thermocouples at 1, 2, 2.5, 3 and 4 meters. Thermocouples were monitored at 10-second increments using a Campbell Scintific CR10 micrologger. AM32 multiplexers switched between the 96 thermocouples involved. An IBM AT compatible computer retrieved and stored data from the micrologger at 10-minute intervals. The data acquisition system was activated shortly after midnight and operated continuously until after sunrise on three near-freeze nights. No significant heating effect was present at any water level. On one of the nights, a refrigeration effect was documented.

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James D. McCurdy, J. Scott McElroy, and Elizabeth A. Guertal

White clover (Trifolium repens L.) inclusion is a proposed means of increasing the sustainability of certain low-maintenance turfgrass scenarios through increased pollinator habitat and as a result of the legume’s ability to biologically fix atmospheric nitrogen (N). Proper white clover establishment is key to maximizing stand uniformity and N contribution to associated grasses. However, there are few guidelines for white clover establishment within warm-season turfgrasses. Four studies were conducted to evaluate seeded white clover establishment within a dormant hybrid bermudagrass [Cynodon transvaalensis Burtt-Davy × C. dactylon (L.) Pers.] lawn as affected by 1) pre-seeding mechanical surface disruption; 2) establishment timing; 3) seeding rate; and 4) companion grass species. White clover establishment was improved by scalping before October seeding, but these effects were not further enhanced by the addition of verticutting or hollow tine aerification. Unscalped turfgrass yielded nearly 50% lower white clover densities than those scalped before seeding, possibly as a result of decreased seed-to-soil contact and increased bermudagrass competition. January and February establishment dates generally yielded the lowest spring clover densities, whereas October timing yielded superior establishment. Clover densities resulting from six seeding rates (0, 0.4, 0.8, 1.5, 3.0, and 6.0 g live seed/m2) were fit to the linear model (y = y 0 + ax b, where y equals trifoliate leaves/m2 and x is equal to initial seeding rate). An important feature of this model was that it accurately represented the diminishing response of increasing seeding rate. Clover establishment was negatively correlated with companion grass densities with the largest densities occurring when planted with tall fescue and the smallest when planted with annual ryegrass. Ultimately, scalping alone or in combination with other mechanical surface disruption should be paired with a clover variety acceptable to the height of cut and the environmental conditions of individual scenarios. Likewise, seeding rates and the decision to include a cool-season companion grass species will be dependent on the use of a turf and the desired green cover.

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Zachary D. Small, James D. McCurdy, Erick D. Begitschke, and Michael P. Richard

Wild garlic (Allium vineale) is an annual winter weed in managed turfgrass. Its dark green, upright stems are easily distinguishable among low-lying, dormant warm-season grasses. Experiments were conducted to determine the effectiveness of synthetic auxin and acetolactate synthase (ALS) inhibiting herbicides for post-emergence control of wild garlic. Trials were conducted in 2016 and 2017. Throughout both trial years, synthetic auxin herbicides exhibited visual control quicker than ALS inhibitors at the initial assessment date 20 d after application (DAA). Conversely, at the final assessment date 49 DAA, ALS inhibitors were the only treatments that controlled wild garlic by more than 85%. In 2016, plots treated with 2,4-D + dicamba + mecoprop at 4 pt/acre exhibited 88% visual control when assessed 20 DAA, but this level had decreased to 51% by 49 DAA. Similarly, visual control in plots treated with 2,4-D + mecoprop + dicamba + carfentrazone-ethyl at 4 pt/acre decreased from 59% to 56% and 82% to 18% between assessment dates in 2016 and 2017, respectively. Metsulfuron-methyl at 0.5 fl oz/acre controlled wild garlic 94% and 91% at the 49 DAA assessment date, whereas sulfentrazone + metsulfuron-methyl at 0.41 lb/acre controlled wild garlic 93% and 95% at the same assessment dates in 2016 and 2017, respectively. Future research should consider tank mixes of auxin-mimicking and ALS-inhibiting herbicides as potential routes for quick burndown and season-long control.

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Te-Ming Tseng, Swati Shrestha, James D. McCurdy, Erin Wilson, and Gourav Sharma

Annual bluegrass (Poa annua L.) is an annual weed that is particularly troublesome in managed turfgrass. It has been controlled conventionally with herbicides, including acetolactate synthase (ALS) inhibitors. However, resistance to ALS inhibitors has been documented throughout the southeastern United States since 2012. A rate response trial was conducted to confirm and determine the resistance level of suspected resistant P. annua biotypes from Mississippi (Reunion), followed by DNA sequencing to determine whether the mechanism of resistance is a target-site mutatio n. In addition, a fitness assay was conducted together with a susceptible biotype to determine whether resistance to ALS inhibitors is associated with decreased fitness. Reunion was at least 45 times more resistant to foramsulfuron than the standard susceptible biotype based on I50 estimates [I50 is the rate of herbicide giving a 50% response (50% visual necrosis)], requiring a predicted 331 g a.i./ha foramsulfuron for 50% control. DNA sequencing results identified a Trp574-to-Leu mutation in the ALS gene of the Reunion biotype, which has been shown by other studies to confer resistance to ALS inhibitors. Measurement of fitness parameters among the Reunion and susceptible biotypes demonstrated reduced seed yield, tillering, and flowering time in the resistant Reunion biotype, suggesting that ALS inhibitor resistance is possibly correlated to decreased fitness in P. annua. Alternative methods to control P. annua need to be considered as a result of the evolution of herbicide-resistant biotypes. An integrated management strategy to control P. annua weeds will help prevent further evolution of resistance. Because this study evaluated only the target-site mechanism of resistance, it is also necessary to determine whether the resistant biotype has reduced uptake, translocation, or enhanced metabolism as additional mechanisms of resistance. Consequently, a fitness study encompassing a more comprehensive list of plant parameters will provide conclusions of the fitness costs associated with ALS inhibitor resistance in P. annua. Chemical names: Foramsulfuron {1-(4,6-dimethoxypyrimidin-2-yl)-3-[2-(dimethylcarbamoyl)-5-formamidophenylsulfonyl] urea}.

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Jordan M. Craft, Christian M. Baldwin, Wayne H. Philley, James D. McCurdy, Barry R. Stewart, Maria Tomaso-Peterson, and Eugene K. Blythe

Traditional hollow-tine (HT) aerification programs can cause substantial damage to the putting green surface resulting in prolonged recovery. Despite the growing interest in new and alternative aerification technology, there is a lack of information in the literature comparing new or alternative technology with traditional methods on ultradwarf bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis (Burtt-Davy)] putting greens. Therefore, the objective of this research was to determine the best combination of dry-injection (DI) cultivation technology with modified traditional HT aerification programs to achieve minimal surface disruption without a compromise in soil physical properties. Research was conducted at the Mississippi State University golf course practice putting green from 1 June to 31 Aug. 2014 and 2015. Treatments included two HT sizes (0.6 and 1.3 cm diameter), various DI cultivation frequencies applied with a DryJect 4800, and a noncultivated control. The HT 1.3 cm diameter tine size had 76% greater water infiltration (7.6 cm depth) compared with the DI + HT 0.6 cm diameter tine size treatment. However, DI + HT 0.6 cm diameter tine size had greater water infiltration at the 10.1 cm depth than the noncultivated control. Results suggest a need for an annual HT aerification event due to reduced water infiltration and increased volumetric water content (VWC) in the noncultivated control treatment. It can be concluded that DI would be best used in combination with HT 1.3 or 0.6 cm diameter tine sizes to improve soil physical properties; however, the DI + HT 0.6 cm diameter tine size treatment resulted in minimum surface disruption while still improving soil physical properties compared with the noncultivated control.

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Erick G. Begitschke, James D. McCurdy, Te-Ming Tseng, T. Casey Barickman, Barry R. Stewart, Christian M. Baldwin, Michael P. Richard, and Maria Tomaso-Peterson

Preemergence herbicides generally have a negative effect on hybrid bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davy] establishment. However, little is known about the effect they have on root architecture and development. Research was conducted to determine the effects of commonly used preemergence herbicides on ‘Latitude 36’ hybrid bermudagrass root architecture and establishment. The experiment was conducted in a climate-controlled greenhouse maintained at 26 °C day/night temperature at Mississippi State University in Starkville, MS, from Apr. 2016 to June 2016 and repeated from July 2016 to Sept. 2016. Hybrid bermudagrass plugs (31.6 cm2) were planted in 126-cm2 pots (1120 cm3) and preemergence herbicide treatments were applied 1 d after planting at the recommended labeled rate for each herbicide. Preemergence herbicide treatments included atrazine, atrazine + S-metolachlor, dithiopyr, flumioxazin, indaziflam, liquid and granular applied oxadiazon, S-metolachlor, pendimethalin, prodiamine, and simazine. Treatments were arranged in a completely randomized design with four replications. Plugs treated with indaziflam and liquid applied oxadiazon failed to achieve 50% hybrid bermudagrass cover by the end of the experiment. Of the remaining herbicide treatments, all herbicides other than granular applied oxadiazon and atrazine increased the number of days required to reach 50% cover (Days50). In addition, all herbicide treatments reduced root mass when harvested 6 weeks after treatment (WAT) relative to the nontreated. By 10 WAT, all treatments reduced root mass in run 1, but during run 2, only prodiamine, pendimethalin, simazine, atrazine + S-metolachlor, liquid applied oxadiazon, and indaziflam reduced dry root mass compared with the nontreated. At 4 WAT, all treatments other than simazine and granular applied oxadiazon reduced root length when compared with the nontreated. By 10 WAT, only dithiopyr, S-metolachlor alone, and indaziflam reduced root length when compared with the nontreated. No differences were detected in the total amounts of nonstarch nonstructural carbohydrates (TNSC) within the roots in either run of the experiment. Results suggest that indaziflam, dithiopyr, and S-metolachlor are not safe on newly established hybrid bermudagrass and should be avoided during establishment. For all other treatments, hybrid bermudagrass roots were able to recover from initial herbicidal injury by 10 WAT; however, future research should evaluate tensile strength of treated sod.