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Andrew J. Hephner, Tyler Cooper, Leslie L. Beck and Gerald M. Henry

The effect of mowing regimens on lateral spread of khakiweed (Alternanthera pungens Kunth) was determined through field studies conducted over a 3-month period in Texas during 2009 and 2010. Treatments were selected to simulate mowing regimens common to intensively managed common bermudagrass [Cynodon dactylon (L.) Pers.] turf and included heights of 1.3 cm (three times/wk), 2.5 cm (two times/week), and 5.1 cm (two times/week). A non-mowed control was included for comparison. Differences in lateral spread of khakiweed among mowing regimens were apparent 4 weeks after initial treatment (WAIT). However, plant diameter increased for all mowing regimens over the course of the trial. Khakiweed plants subjected to the 1.3-cm mowing regimen did not increase in diameter from Week 2 through Week 12, whereas the other two mowing regimens exhibited steady increases in plant diameter over the same time period. By 12 WAIT, non-mowed control plots measured 80.8 cm in diameter, whereas those maintained at 1.3 cm measured 55.3 cm. Comparatively, plants subjected to the 2.5- and 5.1-cm mowing regimens measured 64.7 and 68.8 cm, respectively. Therefore, khakiweed infestations may be more prevalent in bermudagrass mowing heights commonly used for golf course roughs, athletic fields, and home lawns (2.5 cm or greater). However, the production of a thick taproot high in carbohydrate content may enable khakiweed to regenerate from frequent defoliation common to fairway mowing regimes (2.5 cm or less). Adjustments in mowing height may not be enough to effectively reduce khakiweed populations in bermudagrass turf.

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Andrew J. Hephner, Tyler Cooper, Leslie L. Beck and Gerald M. Henry

Khakiweed (Alternanthera pungens Kunth) response to single and sequential herbicide applications was evaluated during the summer of 2009 and 2010 in Texas. No bermudagrass phytotoxicity was observed throughout the length of each trial regardless of herbicide treatment. Carfentrazone at 0.034 kg a.i./ha, metsulfuron + carfentrazone at 0.021 + 0.034 kg a.i./ha, and trifloxysulfuron + carfentrazone at 0.018 + 0.034 kg a.i./ha exhibited 74% to 85% khakiweed control 2 weeks after initial treatment (WAIT) regardless of application regime. Control with carfentrazone (0.017 kg a.i./ha) was only 63% to 65% 2 WAIT regardless of application regime. Metsulfuron and trifloxysulfuron treatments exhibited 54% or less khakiweed control 2 WAIT regardless of rate. Six weeks later (8 WAIT), sequential applications of metsulfuron exhibited 98% control regardless of rate, whereas control with single applications was 79% to 87%. Sequential applications of trifloxysulfuron exhibited 86% to 88% khakiweed control 8 WAIT regardless of rate, whereas single applications exhibited 47% or less control. Carfentrazone treatments exhibited 5% or less control regardless of rate or sequential application 8 WAIT. Tank-mixing metsulfuron or trifloxysulfuron with carfentrazone did not improve control 8 WAIT compared with either sulfonylurea herbicide applied alone. Although initial khakiweed injury was observed in all treatments, effective long-term control was difficult to achieve. Excellent control (95% to 97%) was exhibited by sequential metsulfuron applications 12 WAIT regardless of rate. Sequential applications of trifloxysulfuron (0.018 or 0.028 kg a.i./ha) and single applications of metsulfuron at 0.042 kg a.i./ha exhibited moderate khakiweed control (75% to 80%) 12 WAIT. All other treatments exhibited 57% or less khakiweed control 12 WAIT. Efficacy of sequential metsulfuron applications is a strong incentive for its adoption over trifloxysulfuron applications for the control of khakiweed in bermudagrass turf.

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Gerald M. Henry, Jared A. Hoyle, Leslie L. Beck, Tyler Cooper, Thayne Montague and Cynthia McKenney

Field experiments were conducted at the Central Texas Olive Ranch in Walburg, TX, in 2011 and 2012 to evaluate the efficacy of mulch and/or preemergence herbicides for weed control in high-density olive (Olea europaea L.) production during orchard establishment. Treatments were initiated on 1 Apr. 2011 and 28 Mar. 2012 and consisted of a nontreated control, isoxaben (2.2 kg a.i./ha), oryzalin (4.5 kg a.i./ha), oxadiazon (3.36 kg a.i./ha), and mesotrione (0.14 kg a.i./ha). Hardwood mulch was applied to half of each plot following herbicide application. Weed counts, combined across species (camphorweed, texas croton, lanceleaf sage, pinnate tansymustard, tumble pigweed, common purslane, and prostrate spurge), were conducted to assess % weed cover at 4 and 12 weeks after treatment (WAT). In 2011, compared with the nonmulched no herbicide treatment, adding mulch reduced weed counts by 23 and increased weed control by 70% 4 WAT. All preemergence herbicide treatments, regardless of mulching regime, resulted in ≥97% weed control 4 WAT with the exception of oryzalin without mulch (91% weed control, 3 weeds/plot). In 2012, compared with the nonmulched no herbicide treatment, adding mulch reduced weed counts by 35 and increased weed control by 64% 4 WAT. Mulching in combination with mesotrione resulted in 100% weed control, significantly greater than mesotrione applied without mulch (98%, 2 weeds/plot) 4 WAT. Oryzalin without mulch resulted in greater weed control (94%, 4 weeds/plot) in 2012 4 WAT; however, this treatment provided the least amount of weed control of all preemergence herbicides tested. By 12 WAT, weed counts were reduced by 21 and 22 in 2011 and 2012, respectively, in response to mulching in the nontreated plots resulting in a 52% and 42% increase in weed control in 2011 and 2012, respectively. Mesotrione was the only treatment affected by mulching regime 12 WAT in 2011 and 2012. Mesotrione in combination with mulch resulted in 100% weed control in 2011 and 2012, while mesotrione without mulch resulted in 93% weed control (3 and 4 weeds/plot) 12 WAT in 2011 and 2012, respectively. Although not statistically significant, isoxaben applied alone in 2011 resulted in 97% weed control (1 weed/plot), while isoxaben in combination with mulch resulted in 94% weed control (3 weeds/plot) 12 WAT. In 2011, oryzalin and oxadiazon resulted in 87% to 92% control, regardless of mulching regime 12 WAT. Weed control in response to isoxaben in 2012 was 95% 12 WAT, regardless of mulching regime. The combination of oxadiazon + mulch resulted in similar weed control (95%, 3 weeds/plot) 12 WAT; however, oxadiazon alone and oryzalin with and without mulch resulted in 87% to 89% weed control. All preemergence herbicides evaluated provided good to excellent weed control. Isoxaben and oryzalin are labeled for use on nonbearing fruit trees or during orchard establishment, while oxadiazon is only labeled for woody ornamentals. Although not labeled for use in orchards, mesotrione may be an alternative for use in olive production. The addition of mulching did not increase weed control except when used in conjunction with mesotrione. Mulch alone provided moderate weed control when preemergence herbicides were not applied. Furthermore, the utilization of mulch in combination with preemergence herbicides may help reduce photodegradation and/or volatilization when irrigation/rainfall is limited.

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Gerald M. Henry, James T. Brosnan, Greg K. Breeden, Tyler Cooper, Leslie L. Beck and Chase M. Straw

Indaziflam is an alkylazine herbicide that controls winter and summer annual weeds in bermudagrass (Cynodon sp.) turf by inhibiting cellulose biosynthesis. Research was conducted in Tennessee and Texas during 2010 and 2011 to evaluate the effects of indaziflam applications on overseeded perennial ryegrass (Lolium perenne) establishment and summer annual weed control. In Texas, perennial ryegrass cover on plots treated with indaziflam at 0.75 and 1.0 oz/acre measured 37% to 48% compared with 88% for the untreated control 257 days after initial treatment (DAIT). Perennial ryegrass cover following applications of indaziflam at 0.5 oz/acre measured 84% 257 DAIT and did not differ from the untreated control on any evaluation date. Inconsistent responses in crabgrass (Digitaria sp.) control with indaziflam at 0.5 oz/acre were observed in Tennessee and Texas. However, control was similar to the 0.75-oz/acre rate and prodiamine at 7.8 oz/acre at each location. A September application of indaziflam at 0.75 oz/acre followed by a sequential treatment at 0.5 oz/acre in March of the following year provided >90% control by June 2011. Indaziflam application regimes of this nature would allow for successful fall overseeding of perennial ryegrass every two years and control winter annual weed species such as annual bluegrass (Poa annua).

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Jared. A. Hoyle, Gerald M. Henry, Travis Williams, Aaron Holbrook, Tyler Cooper, Leslie L. Beck and Andrew J. Hephner

Growing concern over the sufficiency and variability of present water supplies in the arid Southwest has led to the examination of buffalograss [Buchloe dactyloides (Nutt.) Engelm.] for water conservation. Increasing acceptance of buffalograss will require investigation into conversion techniques for its establishment. The objectives of this study were to evaluate the effects of seedbed preparation and seeding rate on the establishment of buffalograss after bermudagrass desiccation with glyphosate. Research was conducted at the Texas Tech Quaker Research farm in 2009 and 2010 on a mature ‘Riviera’ common bermudagrass [Cynodon dactylon (L.) Pers.] rough. Bermudagrass was sprayed with glyphosate at 1.1 kg acid equivalent (ae)/ha 5 and 1 weeks before seedbed preparation. Plots were scalped after desiccation. Treatments were arranged in a two × four factorial, randomized complete block design with four replications. two buffalograss seeding rates and four seedbed preparation treatments. Seedbed preparation treatments consisted of no seedbed preparation, topdressing alone (0.6-cm layer), hollow-tine aerification + topdressing, or verticutting + topdressing. ‘TopGun’ buffalograss was planted on 1 June 2009 and 4 June 2010 at 146 or 195 kg·ha−1. Grid counts were conducted to determine buffalograss cover one, two, and three months after planting (MAP). Counts were then converted to percent cover (0% to 100%). Greater buffalograss cover was observed when seed was applied at the higher rate (196 kg·ha−1) except within treatments that did not receive seedbed preparation treatment. No seedbed preparation resulted in unacceptable buffalograss cover. Percent buffalograss cover three MAP was 75%, 83%, and 86% for topdressing alone, aerification + topdressing, and verticutting + topdressing treatments seeded at 195 kg·ha−1, respectively.

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Travis W. Gannon, Matthew D. Jeffries, James T. Brosnan, Gregory K. Breeden, Kevin A. Tucker and Gerald M. Henry

Research was conducted at multiple locations throughout the southeastern United States during 2012 and 2013 to assist turf managers in developing integrated programs for managing crabgrass in common bermudagrass turf. Our objective was to determine the effect of mowing height on the efficacy of several pre-emergent (PRE) herbicides labeled for crabgrass control in bermudagrass turf. Plots were established in Raleigh, NC (NCSU), Knoxville, TN (ETREC), and Winder, GA (UGA) and treated with a factorial combination of two mowing heights (1.5 or 3.8 cm), two application regimes [single or split application (initial and an 8-week sequential)], and six preemergent herbicides (dithiopyr, indaziflam, oxadiazon, pendimethalin, prodiamine, and prodiamine + sulfentrazone). In 2012, all herbicides provided greater crabgrass control on plots maintained at 3.8 cm compared with 1.5 cm. This response was not detected in 2013, potentially as a result of above-average rainfall at two of the three trial locations. Analysis revealed mowing height did not affect pendimethalin soil residue, whereas prodiamine concentrations from bermudagrass maintained at 1.5 cm were greater than bermudagrass maintained at 3.8 cm. Therefore, differences in crabgrass control in bermudagrass maintained under different mowing heights may be the result of plant growth, reduced photosynthetically active radiation (PAR) at the soil surface, among other reasons, and not solely differential degradation of applied herbicides at the 1.5- and 3.8-cm mowing heights. Future research should explore effects of increasing bermudagrass mowing height on PAR required for crabgrass germination and growth.

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Clinton J. Steketee, Alfredo D. Martinez-Espinoza, Karen R. Harris-Shultz, Gerald M. Henry and Paul L. Raymer

Seashore paspalum (Paspalum vaginatum Swartz) is a warm-season turfgrass species primarily used on golf courses and athletic fields, and is often impacted by the disease dollar spot caused by Sclerotinia homoeocarpa F.T. Bennett. Dollar spot is the most common and economically important turfgrass disease in North America, and current management of this disease relies heavily on frequent fungicide applications. An alternate management strategy is host plant resistance, but a better understanding of the interactions between pathogen isolates and the host species is needed to effectively incorporate this resistance into elite seashore paspalum genotypes. The goal of this study was to gather host plant/isolate response data that could be used to develop an effective and efficient screening protocol for resistance to this important disease. Five genotypes of seashore paspalum (‘Aloha’, ‘SeaIsle 2000’, ‘SeaIsle 1’, ‘SeaIsle Supreme’, and 05-1743) varying in dollar spot resistance were inoculated with five isolates of S. homoeocarpa in repeated field studies during 2012 and 2013. Isolates used were from three warm-season and one cool-season turfgrass species. Inoculated plots were evaluated visually and using digital image analysis (DIA) for disease development over time and for number and area of infection centers at two rating dates each year. Statistical differences among the seashore paspalum genotypes and inoculation/isolate treatments were detected for area under the disease progress curve (AUDPC) values, number of infection centers, and infection center area. A significant interaction between seashore paspalum genotype and S. homoeocarpa isolate effects was not observed, indicating that host plant resistance genes are likely not isolate specific. Using this information, breeders should be able to use one highly virulent S. homoeocarpa isolate to screen for host plant resistance in seashore paspalum.