W. Carroll Johnson

Annual Grass Control with Preplant Incorporated and Preemergence Applications of Ethalfluralin and Pendimethalin in PeanutArachis hypogaea1

Abstract: The efficacy of preemergence (PRE) applications of ethalfluralin or pendimethalin incorporated with irrigation was compared with mechanical preplant incorporated (PPI) applications at equivalent rates in peanut. PRE applications of herbicides followed by irrigation were as effective as PPI applications in controlling Texas panicum, southern crabgrass, and crowfootgrass. Split PPI/PRE applications of ethalfluralin were more effective than PPI applications in controlling Texas panicum in 2 of 3 yr. Sequential postemergence applications of clethodim or sethoxydim increased the control of Texas panicum when ethalfluralin or pendimethalin controlled Texas panicum less than 82%. No differences in peanut yield were observed between PPI or PRE applications of either ethalfluralin or pendimethalin. Nomenclature: Clethodim; ethalfluralin; pendimethalin; sethoxydim; crowfootgrass, Dactyloctenium aegyptium (L.) Willd. #3 DTTAE; southern crabgrass, Digitaria ciliaris (Retz.) Koel. # DIGSP; Texas panicum, Panicum texanum Buckl. # PANTE; peanut, Arachis hypogaea L. ‘Georgia Green’. Additional index words: Irrigation. Abbreviations: fb, followed by; PPI, preplant incorporated; PRE, preemergence; POST, postemergence.

Response of Squash and Cucumber Cultivars to Halosulfuron1

Greenhouse studies were conducted to evaluate halosulfuron tolerance of several squash and cucumber cultivars commonly grown in Georgia. There was an inverse linear relationship between squash plant biomass and rate of halosulfuron (r2 = 0.70 to 0.92). With the exception of ‘Supersett’, the slopes from regression of all squash cultivars were equivalent. The estimated amount of halosulfuron required to reduce growth by 20%, based on regression, ranged from 8.2 to 45 g ai/ha (for Supersett and ‘Dixie’, respectively). Squash plant height was also reduced by halosulfuron, though plants began to recover from the injury by the end of the study. There was no effect of halosulfuron rate on cucumber plant biomass or height. Cucumber cultivars appeared to be more tolerant to halosulfuron than did squash cultivars. Nomenclature: Halosulfuron; cucumber, Cucumis sativus L.; squash, Cucurbita pepo L. Additional index words: Cyperus esculentus, Cyperus rotundus, methyl bromide alternatives, MON 12037, purple nutsedge, vegetable weed management, yellow nutsedge. Abbreviations: DAP, days after planting; GR20, herbicide rate required to reduce crop growth 20%; POST, postemergence; PRE, preemergence; PRE–POST, half rate PRE followed by half rate POST.

Effect of Herbicide Application Method on Weed Management and Crop Injury in Transplanted Cantaloupe Production1

Field trials were conducted at the Coastal Plain Experiment Station in Tifton, GA, from 2000 to 2003 to study the effects of herbicide placement on weed control and cantaloupe injury. Herbicides halosulfuron (0.036 kg ai/ha), sulfentrazone (0.14 and 0.28 kg ai/ha), clomazone (0.6 kg ai/ha), and a nontreated control were evaluated. Methods of herbicide application were preplant incorporated (PPI) under the polyethylene mulch before transplanting, posttransplanting over-the-top (POST-OTT), and posttransplanting-directed (POST-DIR) to the shoulders of polyethylene-covered seedbeds. Across all herbicide treatments, PPI and POST-DIR applications were the least injurious, with POST-OTT applications the most injurious. In general, sulfentrazone (0.28 kg ai/ha) was the most injurious herbicide and halosulfuron the least injurious, regardless of herbicide placement. Halosulfuron effectively controlled yellow nutsedge and provided versatility in methods of application, with minimal injury to transplanted cantaloupe. Nomenclature: Clomazone; halosulfuron; sulfentrazone; yellow nutsedge, Cyperus esculentus L. #3 CYPES; cantaloupe, Cucumis melo L. Additional index words: Clomazone, halosulfuron, plasticulture, sulfentrazone. Abbreviations: POST-DIR, posttransplanting-directed; POST-OTT, posttransplanting over-the-top; PPI, preplant incorporated.

Combinations of Corn Gluten Meal, Clove Oil, and Sweep Cultivation are Ineffective for Weed Control in Organic Peanut Production

Abstract Weed control in organic peanut is difficult and lack of residual weed control complicates weed management efforts. Weed management systems using corn gluten meal in combination with clove oil and sweep cultivation were evaluated in a series of irrigated field trials. Corn gluten meal applied in a 30 cm band over the row at PRE, sequentially at PRE+2 wk after emergence, and PRE+2wk+4wk did not adequately control annual grasses and smallflower morningglory. Similarly, a banded application of clove oil applied POST did not adequately control weeds. The only treatment that improved overall weed control was sweep cultivation. Peanut yields were not measured in 2006 due to heavy baseline weed densities and overall poor weed control. Peanut yields were measured in 2007 and were not affected by any weed control treatment due to poor efficacy. While sweep cultivation improved weed control, weeds were controlled only in the row middles and surviving weeds in-row reduced peanut yield. Even when used in combination with sweep cultivation, corn gluten meal and clove oil were ineffective and offer little potential in a weed management system for organic peanut production. Nomenclature: Clove oil; corn gluten meal; crowfootgrass, Dactyloctenium aegyptium (L.) Willd.; goosegrass, Eleusine indica (L.) Gaertn.; smallflower morningglory, Jacquemontia tamnifolia (L.) Griseb.; southern crabgrass, Digitaria ciliaris (Retz.) Koel.; Texas millet, Urochloa texana (Buckl.) R. Webster; peanut, Arachis hypogaea L. Resumen El control de malezas en maní orgánico es difícil, y la carencia de control residual complica aún más los esfuerzos para el manejo de malezas. Se evaluaron sistemas de manejo de malezas incluyendo harina de gluten de maíz en combinación con aceite de trébol y con cultivadores de barrido en una serie de ensayos de campo bajo riego. El gluten de maíz aplicado en una banda de 30 cm sobre la línea de siembra en PRE, secuencialmente a PRE+2 semanas (wk) después de la siembra, y PRE+2wk+4wk no controló adecuadamente malezas gramíneas anuales ni Jacquemontia tamnifolia. Similarmente, una aplicación en banda de aceite de trébol realizada POST no controló adecuadamente las malezas. El único tratamiento que mejoró en forma general el control de malezas fue el cultivo de barrido. Los rendimientos del maní no fueron medidos en 2006 debido a las altas densidades de malezas iniciales y al pobre control de malezas. Los rendimientos del maní se determinaron en 2007 y no fueron afectados por ninguno de los tratamientos de malezas debido a su baja eficacia. Mientras que el cultivo de barrido mejoró el control, las malezas fueron controladas solamente en las zonas centrales entre las líneas de siembra y las malezas que sobrevivieron sobre las líneas de siembra redujeron el rendimiento del maní. Inclusive al usarse en combinación con cultivo de barrido, el gluten de maíz y el aceite de trébol no fueron efectivos y ofrecen muy poco potencial de control en sistemas de manejo de malezas para la producción orgánica de maní.

Implements and Cultivation Frequency to Improve In-Row Weed Control in Organic Peanut Production

Abstract Weed control in organic peanut production is difficult and costly. Sweep cultivation in the row middles is effective, but weeds remain in the crop row, causing yield loss. Research trials were conducted in Ty Ty, GA to evaluate implements and frequencies of cultivation to improve in-row weed control in organic peanut. Implements were a tine weeder and power takeoff-powered brush hoe that targeted weeds present in the row. Frequencies of cultivation were at vegetative emergence of peanut (VE), 1 wk after VE (1wk), 2 wk after VE (2wk), sequential combinations of VE/1wk, VE/2wk, and VE/1wk/2wk. All plots were cultivated with a sweep cultivator to control weeds in row middles. The tine weeder tended to be easier to operate and performed more consistently than the brush hoe. Both implements performed best when initial cultivation was at VE. Delaying the initial cultivation reduced overall effectiveness. Plots with the best in-row weed control were hand-weeded once to control escapes and harvested for peanut yield. The best overall combination of weed control, minimal use of salvage hand-weeding, and maximum peanut yield resulted from sequential cultivation at VE/1wk using either the tine weeder or brush hoe, row middle sweep cultivation, and preharvest mowing. Nomenclature: Smallflower morningglory, Jacquemontia tamnifolia (L.) Griseb.; southern crabgrass, Digitaria ciliaris (Retz.) Koel.; Texas millet, Urochloa texana (Buckl.) R. Webster; peanut, Arachis hypogaea L.

Phytotoxicity of Delayed Applications of Flumioxazin on Peanut (Arachis hypogaea)1

Trials were conducted under weed-free conditions in 2001, 2002, and 2003 on a loamy sand soil in Georgia to investigate the phytotoxicity of flumioxazin on peanut, and in separate trials, the effects on peanut maturity. The first study evaluated time of flumioxazin application (0, 2, 4, 6, 8, and 10 d after planting [DAP]) and flumioxazin rate (nontreated, 71, and 105 g ai/ha). Peanut (variety ‘C99R’) were seeded 3.2 cm deep and irrigated immediately after seeding. Flumioxazin applied to peanut 6, 8, and 10 DAP significantly injured peanut (20 to 59%) early season, with more phytotoxicity from flumioxazin at 105 g/ha than 71 g/ha. However, peanut stand was not reduced by any of the times of application or rates. Peanut recovered by midseason, except in cases of severe (up to 49%) visual phytotoxic injury. Peanut yields were not affected by either flumioxazin application timing or rate. The second study (variety ‘Georgia Green’) evaluated flumioxazin applied at 105 g/ha at varying intervals after planting to determine the phytotoxic effects on peanut maturity using the hull-scrape method. Peanut maturity was delayed by flumioxazin when applied 1 d after planting and later. These results show that the optimum time of application is from immediately after planting to 2 d after planting, but ideally, the application should be made immediately after planting. The highest recommended flumioxazin rate, 105 g/ha, is not significantly phytotoxic when applied within the recommended range of timings and has no effect on yield. However, there is potential for yield loss as peanut maturity is delayed in cases of severe injury. Nomenclature: Peanut, Arachis hypogaea L.; flumioxazin. Additional index words: Hull-scrape method, peanut injury, peanut maturity. Abbreviations: DAE, days after emergence.

Evaluation of Tillage Implements for Stale Seedbed Tillage in Peanut(Arachis hypogaea)1

Abstract: Studies were conducted from 1995 to 1997 near Tifton, GA, to evaluate shallow tillage implements and tillage frequency for stale seedbed weed control in peanut. Tillage implements evaluated were a power tiller, disk harrow, field conditioner, and sweep cultivator. Plots for each implement were tilled once or twice prior to planting peanut. Results from midseason weed counts and peanut yield showed similar responses among implements and frequency of tillage. These results indicate no advantage of any shallow tillage implement for stale seedbed weed control, although peanut yields were generally greater in plots with tilled stale seedbeds than in the nontilled control. The implement of choice should be based on cost of operation and compatibility with the overall peanut production system. Nomenclature: Peanut, Arachis hypogaea L., ‘Georgia Runner’. Key index words: Cultural weed control, groundnut. Abbreviations: DAE, days after emergence; POST, postemergence; PRE, preemergence.

Peanut Response to Naturally-Derived Herbicides Used in Organic Crop Production

Weed-free irrigated trials were conducted in 2004 and 2005 to quantify phytotoxic effects of herbicides with the potential to be used in organic peanut production. Clove oil and citric plus acetic acid were each applied at vegetative emergence of peanut (VE), two weeks after VE (2 wk), four weeks after VE (4 wk), sequentially VE/2 wk, sequentially VE/4 wk, sequentially VE/2 wk/ 4 wk, and a nontreated control. Clove oil was more injurious (maximum of 28% visual injury) than citric plus acetic acid (maximum of 4% visual injury), with significant injury occurring with clove oil applied at 4-wk or sequentially. Citric plus acetic acid caused minimal peanut injury. There were no consistent effects of clove oil on peanut yield, although sequential applications of clove oil tended to reduce peanut yield. Peanut yield was not affected by citric plus acetic acid.

Interactive Effects of Soil pH, Halosulfuron Rate, and Application Method on Carryover to Turnip Green and Cabbage

Abstract Field studies were conducted in 2006 and 2007 to evaluate the tolerance of autumn-planted cabbage and turnip green to halosulfuron applied the previous spring to cantaloupe. Main plots were three levels of soil pH: maintained at a natural pH level, pH raised with Ca(OH)2, and pH lowered with Al2(SO4)3. Subplots were a factorial arrangement of two halosulfuron application methods and three halosulfuron rates. Halosulfuron application methods were PPI or POST after transplanting to the edges of mulch-covered seedbeds. Halosulfuron rates were 35 and 70 g ai/ha, along with a nontreated control. Cantaloupe were transplanted, maintained weed-free, and evaluated for yield response. After cantaloupe harvest, direct-seeded turnip green and transplanted cabbage were established in September of each year and evaluated for crop tolerance and yield. Data indicated nonsignificant main effects of soil pH and halosulfuron application method on cantaloupe yield. However, in 2007 cantaloupe yields were significantly reduced, by 16 and 20% for halosulfuron applied at 35 and 70 g/ha, respectively. For all turnip green and cabbage response parameters, interactions were nonsignificant between application method and rate, soil pH and rate, and soil pH and application method, along with the three-way interaction. After 6 mo, there was no evidence of stunting from halosulfuron carryover in 2006 to direct-seeded turnip green and in both years to transplanted cabbage. Visual estimates of stunting to direct-seeded turnip green ranged from 9 to 16% for halosulfuron at 35 and 70 g/ha, respectively, in 2007, but all stunting was transient and turnip green yield was not affected.

Cultural Practices to Improve In-Row Weed Control with Cultivation in Organic Peanut Production

Abstract Cultivation is a proven means of weed control in organic peanut. However, weeds present in-row often escape control. Research trials were conducted in Ty Ty, GA to modify cultural practices to help suppress weed emergence in-row. Modified cultural practices were three row pattern/seeding rate combinations; twin rows (four rows on a seedbed) seeded at the recommended (1X) seeding rate that produced 13 seed m−1 in each row, twin rows seeded at the 2X seeding rate that produced 23 seed m−1 in each row, and wide rows (two rows on seedbed) seeded at the recommended seeding rate that produced 23 seed m−1. Four cultivation regimes were evaluated; cultivation with a tine weeder at weekly intervals for 6 wk, cultivation with a tine weeder at weekly intervals for 8 wk, scouring with a brush hoe at vegetative emergence followed by the tine weeder for 6 wk, and a noncultivated control. There were no interactions between row pattern/seeding rates and cultivation regimes for any parameter measured. There was inconsistent response of weed control and peanut yield to row pattern/seeding rates. Weed control and peanut yields were similar with tine weeding for 6 wk, 8 wk, or with the brush hoe followed by the tine weeder. Weed management in organic peanut was not improved by altering peanut cultural practices that facilitate quicker canopy closure, and the use of narrow row patterns should not be based on attempts to improve weed control in organic peanut. Narrow row patterns provide other benefits to organic peanut production and those attributes should influence decisions on the choice of row pattern, not weed control. Nomenclature: Crowfootgrass, Dactyloctenium aegyptium (L.) Willd.; Florida beggarweed, Desmodium tortuosum (Sw.) DC.; pitted morningglory, Ipomoea lacunosa L.; sicklepod, Senna obtusifolia (L.) H.S. Irwin & Barneby; smallflower morningglory, Jacquemontia tamnifolia (L.) Griseb.; southern crabgrass, Digitaria ciliaris (Retz.) Koel.; peanut, Arachis hypogaea L. Resumen Cultivar es un método comprobado para el control de malezas en maní orgánico. Sin embargo, las malezas presentes en la línea de siembra a menudo escapan al control. Se realizaron estudios en Ty Ty, GA para modificar las prácticas culturales para ayudar a suprimir la emergencia de malezas en la línea de siembra. Las prácticas culturales modificadas fueron tres combinaciones de patrones y de densidades de siembra; líneas gemelas (cuatro líneas en cada cama de siembra) sembradas a la densidad recomendada (1X) que produjo 13 semillas m−1 en cada línea, líneas gemelas sembradas a una densidad 2X que produjo 23 semillas m−1 en cada línea, y líneas amplias (2 líneas por cama de siembra) sembradas a la densidad recomendada lo que produjo 23 semillas m−1. Se evaluaron cuatro regímenes de cultivo; cultivo semanal con un rastrillo de púas durante 6 semanas, cultivo semanal con rastrillo de púas durante 8 semanas, barrido con azadón de cepillo al momento de emergencia vegetativa seguido por un cultivo con el rastrillo de púas durante 6 semanas, y un tratamiento testigo sin cultivo. No hubo interacciones entre el patrón/densidad de siembra y el régimen de cultivo para ninguno de los parámetros medidos. La respuesta al patrón/densidad de siembra en control de malezas y rendimiento del maní fue inconsistente. El control de malezas y los rendimientos del maní fueron similares con el cultivo con el rastrillo de púas durante 6 y 8 semanas, o con el azadón de cepillo seguido por el rastrillo de púas. El manejo de malezas en maní orgánico no mejoró al alterar las prácticas culturales que facilitaron un cierre del dosel más rápido. El uso de patrones angostos de líneas de siembra no debería enfocarse en intentos para mejorar el control de malezas en maní orgánico. Patrones angostos de líneas de siembra brindan otros beneficios en la producción de maní orgánico y deberían ser estos otros atributos, y no el control de malezas, los que influencien las decisiones sobre la escogencia de patrones de siembra.