Peter A. Dotray

Biological Control of Woollyleaf Bursage (Ambrosia grayi) with Pseudomonas syringae pv. tagetis1

Abstract: Field studies were conducted with a biocontrol agent, Pseudomonas syringae pv. tagetis, to determine the optimal application parameters for controlling woollyleaf bursage, a pernicious perennial weed on the Texas Southern High Plains. Parameters investigated were bacterial concentration, time, season, and frequency of application. Pseudomonas syringae pv. tagetis concentration ranging from 104 to 108 colony forming units (CFU)/ml produced similar incidence of disease on woollyleaf bursage. Weekly, biweekly, and triweekly applications were found to be equally effective. Optimal time for application of P. syringae pv. tagetis was at midday. A single application in April, May, or June resulted in higher incidence of disease for 5 wk than the noninoculated plots, whereas single applications in July and August were not consistently different from the noninoculated plots. Weed density was negatively correlated with disease incidence for April, July, and August applications, particularly when correlations were based on disease incidence from 1 to 4 wk prior to weed density measurement. Weed densities during 1997 were lower at the end of the year when bacteria applications were made in April, May, or June, as opposed to July or August, or plots were not inoculated. In 1998, weed density was lower when bacteria applications were made in April as opposed to May or June. These investigations indicate that P. syringae pv. tagetis does infect woollyleaf bursage on the Texas southern High Plains. Nomenclature: Woollyleaf bursage; Ambrosia grayi (A. Nels.) Shinners #3 AMBGR; Pseudomonas syringae pv. tagetis; biological control. Additional index words: Biological control agent, biopesticide. Abbreviations: AT, application time; B, bacteria; CFU, colony forming units; EP, evaluation period; IOD, incidence of disease.

Peanut Yield Response to Dicamba

Abstract Research was conducted at eight locations across the United States peanut belt during 2008 to evaluate peanut response to postemergence applications of dicamba. Dicamba was applied at 0, 4...

Weed Control and the Use of Herbicides in Sesame Production

Sesame (Sesamum indicum L.) is one of the oldest crops known to humans. There are archeological remnants of sesame dating to 5,500 BC in the Harappa Valley in the Indian subcontinent (Bedigian & Harlan, 1986). Assyrian tablets from 4,300 BC in a British museum described how the gods ate bread and drank sesame wine together before battles to restore order to the universe (Weiss, 1971). Most people remember the words “Open sesame” from Ali Baba and the 40 Thieves to open a cave full of riches. It is similar to the sesame capsules because their opening produced great riches. Sesame was a major oilseed in the ancient world because of its ease of extraction, great stability, and drought resistance. In India today, almost as in the olden days, a farmer can take his crop to an expeller that consists of grinding mortar and pestle stones driven by a bullock. He can place the oil in a vessel, take it back to his home and have cooking oil for a year without the oil going rancid (S.S. Rajan, personal communication). Sesame is a survivor crop. It has been planted for over 7,500 years in Asia and Africa in very poor growing conditions. In parts of Thailand, farmers broadcast the seed and came back at the end of the season and see which plant had won – the sesame or the weeds (W. Wongyai, personal communication). More often than not, the sesame won. Sesame cultivars in those areas were tall, had very long internodes, and grew above the weeds. In Rajasthan, India, sesame is the last crop that can be grown adjacent to the deserts under extreme dry conditions. In several droughts in the U.S., sesame was the only crop that survived without irrigation (Langham & Wiemers, 2002). Although this chapter draws from research from many countries, the emphasis is on herbicides in the U.S., the only country where sesame is completely mechanized and where herbicides are critical for economic production. Sesame was introduced to the U.S. from Africa and was called beni/benne/benni. Betts (1999) quotes letters from Thomas Jefferson that document his trials with sesame between 1808 and 1824. Jefferson stated that sesame “...is among the most valuable acquisitions our country has ever made. ... I do not believe before that there existed so perfect a substitute for olive oil.” He talks about the rule of thumb that still exists today that sesame will do well where cotton (Gossypium hirsutum L.) does well. Sesame was produced in Texas on a limited scale during the 1950’s and early 1960’s, first in northeast Texas and later shifting to the High Plains, where consistent yield increases resulted from irrigation and more favorable climate conditions (Brigham & Young,

Castor (Ricinus communis L.) Tolerance to Postemergence Herbicides and Weed Control Efficacy

Potential US castor production is limited due to only one labeled herbicide (trifluralin). Field studies were conducted at two Texas locations during 2008 and 2009 to evaluate postemergence herbicides for castor tolerance and weed control efficacy. Clethodim and fluazifop-P-butyl caused no castor stunting while acifluorfen, bentazon, imazethapyr, and lactofen caused stunting which ranged from 5 to 46%. Imazapic and 2,4-DB caused the greatest stunting (44 to 99%) and resulted in castor yields of 0 to 45% of the untreated check. Acifluorfen, imazapic, imazethapyr, lactofen, and 2,4-DB controlled at least 80% smellmelon (Cucumis melo L. var. Dudaim Naud.) while clethodim and fluazifop-P-butyl controlled at least 98% Texas millet [Urochloa texana (Buckl.) R.Webster]. Imazapic and imazethapyr provided 57 to 75% Texas millet control. Results suggest that castor tolerance to the graminicides, clethodim, and fluazifop-P-butyl is high; however, castor injury and yield reductions with the postemergence applications of broadleaf herbicides suggest that these herbicides should not be used in castor production.

Weed Control and Grain Sorghum (Sorghum bicolor) Tolerance to Pyrasulfotole plus Bromoxynil

Field studies were conducted during the 2008 and 2009 growing seasons at five locations in the Texas grain sorghum producing regions to evaluate pyrasulfotole plus bromoxynil combinations for weed control and grain sorghum response. All pyrasulfotole plus bromoxynil combinations controlled Amaranthus palmeri, Cucumis melo, and Proboscidea louisianica at least 94% while control of Urochloa texana was never better than 69%. Pyrasulfotole plus bromoxynil combinations did result in early season chlorosis and stunting; however, by the end of the growing season no visual injury or stunting differences were noted when compared to the untreated check. Early season grain sorghum chlorosis and stunting with pyrasulfotole plus bromoxynil combinations did not affect grain sorghum yields with the exception of pyrasulfotole at 0.03 kg ai/ha plus bromoxynil at 0.26 kg ai/ha plus atrazine at 0.58 kg ai/ha applied early postemergence followed by pyrasulfotole plus bromoxynil applied mid-postemergence which reduced yield at one of two locations in 2008. Grain sorghum yield increased following all pyrasulfotole plus bromoxynil treatments compared to the untreated check in 2009.

Glufosinate Application Timing and Rate Affect Peanut Yield

ABSTRACT Field studies were conducted at 13 locations across the US peanut belt during 2010–2012 to evaluate peanut response to postemergence applications of glufosinate. Glufosinate was applied at...

Yellow Nutsedge (Cyperus Esculentus) Control and Peanut Tolerance to S-Metolachlor and Diclosulam Combinations

Field studies were conducted in different peanut-growing areas of Texas during the 1999 through 2001 growing seasons to evaluate yellow nutsedge control and peanut tolerance to diclosulam alone applied PRE, S-metolachlor alone applied POST, or diclosulam applied PRE followed by (fb) S-metolachlor applied POST. Yellow nutsedge control was > 80% at five of six locations when diclosulam at 0.018 or 0.026 kg/ha applied PRE was fb S-metolachlor applied POST at 0.56, 1.12, or 1.46 kg ai/ha. Peanut stunting was noted with diclosulam at the High Plains locations but not at the Rolling Plains or south Texas locations. This stunting with diclosulam was due to a combination of peanut variety and high soil pH. Peanut yield was not always increased where yellow nutsedge was controlled. Nomenclature: Diclosulam, N-(2,6-dichlorophenyl)-5-ethoxy-7-fluoro[1,2,4]triazolo[1,5-c]pyrimidine-2-sulfonamide; S-metolachlor; yellow nutsedge, Cyperus esculentus L. CYPES; peanut, Arachis hypogaea L., ‘Flavor Runner 458’, ‘Florunner’, ‘Georgia Green’

Cotton Stage of Growth Determines Sensitivity to 2,4-D

The anticipated release of EnlistTM cotton, corn, and soybean cultivars likely will increase the use of 2,4-D, raising concerns over potential injury to susceptible cotton. An experiment was conducted at 12 locations over 2013 and 2014 to determine the impact of 2,4-D at rates simulating drift (2 g ae ha−1) and tank contamination (40 g ae ha−1) on cotton during six different growth stages. Growth stages at application included four leaf (4-lf), nine leaf (9-lf), first bloom (FB), FB + 2 wk, FB + 4 wk, and FB + 6 wk. Locations were grouped according to percent yield loss compared to the nontreated check (NTC), with group I having the least yield loss and group III having the most. Epinasty from 2,4-D was more pronounced with applications during vegetative growth stages. Importantly, yield loss did not correlate with visual symptomology, but more closely followed effects on boll number. The contamination rate at 9-lf, FB, or FB + 2 wk had the greatest effect across locations, reducing the number of bolls per plant when compared to the NTC, with no effect when applied at FB + 4 wk or later. A reduction of boll number was not detectable with the drift rate except in group III when applied at the FB stage. Yield was influenced by 2,4-D rate and stage of cotton growth. Over all locations, loss in yield of greater than 20% occurred at 5 of 12 locations when the drift rate was applied between 4-lf and FB + 2 wk (highest impact at FB). For the contamination rate, yield loss was observed at all 12 locations; averaged over these locations yield loss ranged from 7 to 66% across all growth stages. Results suggest the greatest yield impact from 2,4-D occurs between 9-lf and FB + 2 wk, and the level of impact is influenced by 2,4-D rate, crop growth stage, and environmental conditions. Nomenclature: 2,4-D; cotton, Gossypium hirsutum L. La anticipada liberación de cultivares Enlist™ de algodón, maíz, y soja probablemente incrementará el uso de 2,4-D, aumentando así la preocupación del daño potencial en algodón susceptible. Se realizó un experimento en 12 localidades durante 2013 y 2014 para determinar el impacto de 2,4-D a dosis de deriva simulada (2 g ae ha−1) y de contaminación en tanque (40 g ae ha−1) sobre algodón durante seis estadios de crecimiento diferente. Los estadios de crecimiento al momento de aplicación incluyeron cuatro hojas (4-lf), nueve hojas (9-lf), primer brote florar (FB), FB + 2 semanas (wk), FB + 4 wk, y FB + 6 wk. Las localidades fueron agrupadas según el porcentaje de pérdida de rendimiento al compararse con el testigo sin tratamiento (NTC), teniendo el grupo I la menor pérdida de rendimiento y el grupo III la mayor. La epinastia producto de 2,4-D fue más pronunciada con aplicaciones durante los estadios de crecimiento vegetativo. Importantemente, la pérdida en el rendimiento no correlacionó con la sintomatología visual, pero siguió de cerca los efectos en el número de frutos. La dosis de contaminación a 9-lf, FB, o FB + 2 wk tuvo el mayor efecto en todas las localidades, reduciendo el número de frutos por planta cuando se comparó con el NTC, pero sin tener efecto cuando se aplicó en FB + 4 wk o después. La reducción en el número de frutos no fue detectable con la dosis de deriva excepto en el grupo III cuando se aplicó en el estadio FB. El rendimiento fue influenciado por la dosis de 2,4-D y el estadio de crecimiento del algodón. Considerando todas las localidades, las pérdidas de rendimiento mayor a 20% ocurrieron en 5 de 12 localidades cuando se aplicó la dosis de deriva entre 4-lf y FB + 2 wk (mayor impacto a FB). Para la dosis de contaminación, la pérdida en rendimiento fue observada en todas las 12 localidades. Al promediar todas las localidades, la pérdida de rendimiento varió entre 7 y 66% entre todos los estadios de crecimiento. Los resultados sugieren que el mayor impacto en el rendimiento causado por 2,4-D ocurre entre 9-lf y FB + 2 wk, y el nivel de impacto es influenciado por la dosis de 2,4-D, el estadio de crecimiento, y las condiciones ambientales.

Cotton (Gossypium hirsutum) Tolerance to Propazine Applied Pre- and Postemergence

Abstract Field studies were conducted in 2007 and 2008 near Lubbock and Lamesa, TX, to determine the effects of propazine alone and in combination with glyphosate applied PRE and POST on cotton growth, yield, and lint value (fiber quality). Propazine at 0.56, 0.84, and 1.12 kg ai ha−1 and in combination with glyphosate at 0.86 kg ae ha−1 was applied PRE, early POST, and mid-POST. Up to 11% injury was observed after propazine applied early POST and mid-POST at Lubbock in 1 of 2 yr, and up to 13% at all three application timings was observed at Lamesa in 1 of 2 yr. The greatest injury was observed 58 d after application following propazine at 1.12 kg ai ha−1 applied PRE; however, no injury was apparent 80 d after application. Cotton yield, lint values, and gross revenues were not affected by any treatment. Nomenclature: Glyphosate; propazine; cotton, Gossypium hirsutum ‘FiberMax 9058 F’, ‘Americot 1532 B2RF’

Peanut Response to Carfentrazone-ethyl and Pyraflufen-ethyl Applied Postemergence1

Abstract Field experiments were conducted at six locations in Texas in 2004 and 2005 to evaluate peanut tolerance to carfentrazone-ethyl and pyraflufen-ethyl. Carfentrazone-ethyl at 27 and 36 g ai/ha or pyraflufen-ethyl at 2.6 and 3.5 g ai/ha were applied early postemergence (EP) 28 to 51 days after planting (DAP) or late postemergence (LP) 93 to 121 DAP in weed-free plots. In the Texas High Plains, carfentrazone-ethyl and pyraflufen-ethyl applied EP resulted in 62 and 48% visual injury, respectively, when rated 14 days after treatment (DAT). With the exception of the low rate of carfentrazone-ethyl at one location, this injury was greater than the injury caused by paraquat at 210 g ai/ha plus bentazon at 280 g ai/ha. All injury declined over time, but was still apparent at harvest (up to 3%). Peanut injury from applications made late postemergence did not exceed 16%. In the Rolling Plains, peanut injury did not exceed 12% at Lockett and 25% at Rochester regardless of herbicide, rate, or timing. In south ...