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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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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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Tyler Cooper, Leslie L. Beck, Chase M. Straw and Gerald M. Henry

Metamifop is a postemergence aryloxyphenoxypropionic acid herbicide used for the control of annual and perennial grass weeds in cereal crops and rice (Oryza sativa L.). Previous research observed creeping bentgrass (Agrostis stolonifera L.) tolerance to applications of metamifop, suggesting utilization for the removal of encroaching bermudagrass (Cynodon Rich.) from creeping bentgrass putting greens with little to no phytotoxicity. Therefore, the objective of our research was to evaluate the efficacy of metamifop for common bermudagrass [Cynodon dactylon (L.) Pers.] control in a greenhouse environment. Experiments were conducted at the Plant and Soil Science greenhouse facility at Texas Tech University in Lubbock in 2011 and 2012. ‘Riviera’ and ‘Savannah’ common bermudagrass were seeded at 218 lb/acre into 4-inch square pots containing a soilless potting media on 26 Aug. 2011 and 14 Nov. 2011. Pots were allowed to mature in the greenhouse over a 3-month period where they were maintained at a height of 0.25 inches. Herbicide treatments were applied on 1 Dec. 2011 and 8 Feb. 2012 and consisted of metamifop at 0.18, 0.27, 0.36, or 0.45 lb/acre. A sequential application of each treatment was made on 22 Dec. 2011 and 29 Feb. 2012. A nontreated control was included for comparison. Clipping ceased after initial herbicide treatment and pots produced biomass for 3 weeks. Biomass above 0.25 inch was removed from each pot, dried, and weighed. This procedure was conducted again 3 weeks after sequential treatments. The rate of metamifop required to reduce bermudagrass growth 50% (GR50) was calculated 3 and 6 weeks after initial treatment (WAIT). Visual ratings of percent bermudagrass control were recorded weekly on a scale of 0% (no control) to 100% (completely dead bermudagrass). As metamifop rate increased, bermudagrass biomass decreased. The calculated GR50 at 3 WAIT for ‘Savannah’ and ‘Riviera’ was 0.19 and 0.14 lb/acre, respectively. Nontreated control pots exhibited 0% control and produced 0.59 to 0.83 g of biomass at 3 WAIT, regardless of cultivar. Metamifop at 0.27 to 0.45 lb/acre exhibited 96% to 100% bermudagrass control at 3 WAIT, regardless of cultivar. Bermudagrass subjected to those same treatments only produced 0.01 to 0.03 g of biomass at 3 WAIT, regardless of cultivar. The 0.18-lb/acre rate of metamifop exhibited only 9% control of ‘Savannah’ bermudagrass with 0.72 g of biomass collected, while ‘Riviera’ was controlled 41% with 0.38 g of biomass collected. The calculated GR50 at 6 WAIT for ‘Savannah’ and ‘Riviera’ was 0.13 and 0.14 lb/acre, respectively. Sequential applications of metamifop at 0.27 to 0.45 lb/acre completely controlled bermudagrass (100%) at 6 WAIT, while a sequential application at 0.18 lb/acre only controlled bermudagrass 8% to 19% at 6 WAIT, regardless of cultivar. Bermudagrass subjected to 0.18 lb/acre exhibited 0.48 to 0.56 g of biomass at 6 WAIT, regardless of cultivar. Metamifop shows potential as an alternative control option for common bermudagrass present within cool-season turfgrass species.

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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, 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.