Harold D. Coble

Interference of Common Cocklebur ( Xanthium strumarium ) and Cotton ( Gossypium hirsutum )

An area of influence method with biweekly destructive harvests 5 through 19 wk after planting (WAP) was used to monitor the reciprocal interference of common cocklebur and cotton in 1987 and 1988. Plant heights, leaf area, and leaf, stem, boll, fiber, and total plant biomass dry weights were measured in 15-cm increments away from common cocklebur or from a randomly selected cotton plant out to 105 cm. Data indicated that cotton less than 60 cm from common cocklebur was shorter, had less leaf area and lower leaf, stem, boll, and biomass dry weights than cotton beyond 60 cm from common cocklebur or cotton grown without common cocklebur interference. Differences in leaf area and biomass between cotton grown with and without common cocklebur interference were greater at and beyond 13 WAP sample dates than before 13 WAP. By 15 WAP, cotton leaf area and biomass were reduced an estimated 11% and 15%, respectively, averaged over the entire 105 cm of row. Cotton yield, harvested 27 WAP, was reduced an estimated 31% on plants grown with one common cocklebur plant per 2.1 m. Cotton yield was reduced on plants out to 99 cm from common cocklebur. Common cocklebur and cotton plants grown alone were taller, had greater leaf area, and greater leaf, stem, and biomass dry weight than those respective plants grown adjacent to cotton. Common cocklebur grown alone produced 67% more biomass than did cotton grown alone. Cotton plants grown adjacent to other cotton plants produced 89% and 96% less boll and fiber weight, respectively, than plants grown alone.

Effect of mowing on perennial sedges

Abstract Field studies were conducted in 1996 and 1997 to determine the response of Cyperus rotundus and Cyperus esculentus, Kyllinga brevifolia, and Kyllinga gracillima to mowing regimens common to recreational turfgrass. Treatments were selected to simulate Cynodon dactylon golf course management and included mowing at 1.3 and 3.8 cm with mowing frequencies of three times per week and once a week, respectively. A nonmowed check was included for comparison. Reductions in C. rotundus shoot number were observed beginning 6 wk after initial treatment (WAIT) in 1996 and 9 WAIT in 1997 for the 1.3-cm mowing regime. The 3.8-cm mowing regime did not reduce C. rotundus shoot number until the final evaluation of each year. Reductions in C. rotundus rhizome length, tuber number, and tuber size were observed for both mowing regimes in both years. Cyperus esculentus shoot number was reduced by the 1.3-cm treatment at each evaluation date in 1996 and 1997. Cyperus esculentus shoot number reductions in the 3.8-cm regime were first observed 4 and 6 WAIT in the 2 yr and continued until termination. The 1.3-cm regime reduced C. esculentus spread beginning 6 WAIT in 1996 and 3 WAIT in 1997. Cyperus esculentus spread was also reduced by the 3.8-cm treatment, but reduction began at later evaluations (8 and 9 WAIT). Tuber production by C. esculentus was completely inhibited by the two mowing regimes in both years. The only treatment effect observed in K. brevifolia and K. gracillima in 1996 was a reduction in internode length of K. gracillima by the 1.3-cm mowing regime. In 1997, the 1.3-cm regime reduced K. brevifolia shoot number at 15 and 18 WAIT and plant spread beginning 6 WAIT and continuing until termination. The 3.8-cm treatment did not affect K. brevifolia shoot number and reductions in spread were only observed at the final evaluation. Kyllinga gracillima shoot number and plant spread were reduced by the 1.3-cm mowing regime at each 1997 evaluation. Reductions in K. gracillima shoot number occurred at the final evaluation, and reductions in spread began 12 WAIT when subjected to the 3.8-cm treatment. Both mowing regimes reduced K. brevifolia and K. gracillima internode length. Kyllinga brevifolia total rhizome length and total node number were reduced by the 1.3-cm regime only. Kyllinga gracillima rhizome length, internode length, and node number were reduced by both regimes in 1997. Nomenclature:Cynodon dactylon (L.) Pers., bermudagrass; Cyperus rotundus L. CYPRO, purple nutsedge; Cyperus esculentus L. CYPES, yellow nutsedge; Kyllinga brevifolia Rottb. KYLBR, green kyllinga; Kyllinga gracillima Miq. KYLGR, false green kyllinga.

Absorption, translocation, and metabolism of 14C-glufosinate in Xanthium strumarium, Commelina difusa, and Ipomoea purpurea

Abstract The absorption, translocation, and metabolism of glufosinate were investigated in three differentially susceptible weeds, Xanthium strumarium (most susceptible), Ipomoea purpurea (intermediate susceptibility), and Commelina diffusa (least susceptible). Xanthium strumarium absorbed about three times more 14C-glufosinate than Ipomoea purpurea and about six times more 14C-glufosinate than Commelina diffusa. Translocation of the applied herbicide out of the treated leaf was low. No evidence of glufosinate metabolism, either in the treated leaves or roots, was found when the extracts were separated by HPLC. Nomenclature: Glufosinate; Xanthium strumarium L. XANST, common cocklebur; Commelina diffusa Burm. f. COMDI, spreading dayflower; Ipomoea purpurea (L.) Roth. PHBPU, tall morningglory.

An economic analysis of binomial sampling for weed scouting

Abstract Full-count random sampling has been the traditional method of obtaining weed densities. Currently it is the recommended scouting procedure when using HERB, a herbicide selection decision aid. However, alternative methods of scouting that are quicker and more economical need to be investigated. One possibility that has been considered is binomial sampling. Binomial sampling is the procedure by which density is estimated from the number of random quadrats in which the count of individuals is equal to or less than a specified cutoff value. This sampling method has been widely used for insect scouting. There has also been interest in using binomial sampling for weed scouting. However, an economic analysis of this sampling method for weeds has not been performed. In this paper, the results of an economic analysis using simulations with binomial sampling and the HERB model are presented. Full-count sampling was included in the simulations to provide a benchmark for comparison. The comparison was made in terms of economic losses incurred when the estimated weed density obtained from sampling was inaccurate and a herbicide treatment was selected that did not maximize profits. These types of losses are referred to as opportunity losses. The opportunity losses obtained from the simulations indicate that in some situations binomial sampling may be a viable economic alternative to full-count sampling for fields with weed populations that follow a negative binomial distribution, assuming no prior knowledge of weed densities or negative binomial k values. Nomenclature: Glycine max, soybeans.

Influence of Palmer Amaranth (Amaranthus palmeri ) on the Critical Period for Weed Control in Plasticulture-Grown Tomato

Abstract Field studies were conducted in 1996, 1997, and 1998 at Clinton, NC, to determine the influence of Palmer amaranth establishment and removal periods on the yield and quality of plasticulture-grown ‘Mountain Spring fresh market tomato. Treatments consisted of 14 Palmer amaranth establishment and removal periods. Half of the treatments were weed removal treatments (REM), in which Palmer amaranth was sowed at the time tomato transplanting and allowed to remain in the field for 0 (weed-free all season), 2, 3, 4, 6, 8, or 10 wk after transplanting (WAT). The second set of the treatments, weed establishment treatments (EST), consisted of sowing Palmer amaranth 0 (weedy all season), 2, 3, 4, 6, 8, or 10 WAT and allowing it to grow in competition with tomato the remainder of the season. Tomato shoot dry weight was reduced 23, 7, and 11 g plant−1 for each week Palmer amaranth removal was delayed from 0 to 10 WAT in 1996, 1997, and 1998, respectively. Marketable tomato yield ranged from 87,000 to 41,000 kg ha−1 for REM of 0 to 10 WAT and 28,000 to 88,000 kg ha−1 for EST of 0 to 6 WAT. Percentage of jumbo, large, medium, and cull tomato yields ranged from 49 to 33%, 22 to 31%, 2 to 6%, and 9 to 11%, respectively, for REM of 0 to 10 WAT and 30 to 49%, 38 to 22%, 3 to 2%, and 12 to 9%, respectively, for EST of 0 to 6 WAT. To avoid losses of marketable tomato yield and percentage of jumbo tomato fruit yield, tomato plots must remain free of Palmer amaranth between 3 and 6 WAT. Observed reduction in marketable tomato yield was likely due to competition for light as Palmer amaranth plants exceeded the tomato plant canopy 6 WAT and remained taller than tomato plants for the remainder of the growing season. Nomenclature: Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA; tomato, Lycopersicon esculentum L. ‘Mountain Spring. Resumen En 1996, 1997 y 1998, se realizaron estudios de campo en Clinton, North Carolina, para determinar la influencia del establecimiento y momento de remoción de Amaranthus palmeri en el rendimiento y la calidad del tomate para el mercado fresco Mountain Spring producido con cobertura plástica. Los tratamientos consistieron en 14 períodos de establecimiento y remoción de A. palmeri. La mitad de los tratamientos fueron de remoción de la maleza (REM), en los cuales se sembró A. palmeri al momento del trasplante del tomate y se mantuvo en el campo por 0 (libre de malezas a lo largo de toda la temporada), 2, 3, 4, 6, 8 ó 10 semanas después del trasplante (WAT). El segundo grupo de tratamientos, establecimiento de la maleza (EST), consistió en la siembra de A. palmeri a 0 (enmalezado durante toda la temporada), 2, 3, 4, 6, 8 ó 10 WAT y permitiéndole crecer en competencia con el tomate durante el resto de la temporada. El peso seco de la parte aérea del tomate se redujo 23, 7 y 11 g planta−1 por cada semana que se retrasó la remoción de A. palmeri desde 0 a 10 WAT en 1996, 1997 y 1998, respectivamente. El rendimiento de tomate comercializable varió entre 87,000 a 41,000 kg ha−1 para REM de 0 a 10 WAT y 28,000 a 88,000 kg ha−1 para EST de 0 a 6 WAT. El porcentaje del rendimiento de tomates “jumbo”, grande, mediano y de rechazo varió de 49 a 33%, 22 a 31%, 2 a 6% y 9 a 11%, respectivamente para REM de 0 a 10 WAT y 30 a 49%, 38 a 22%, 3 a 2% y 12 a 9%, respectivamente para EST de 0 a 6 WAT. Para evitar pérdidas de rendimiento de tomate comercializable y de porcentaje de rendimiento de fruta jumbo, las parcelas de tomate deben permanecer libres de A. palmeri entre 3 y 6 WAT. Las reducciones en el rendimiento de tomate comercializable se debieron probablemente a la competencia por luz, ya que las plantas de A. palmeri sobrepasaron el dosel de las plantas de tomate a 6 WAT y se mantuvieron más altas que las plantas de tomate por el resto de la temporada de crecimiento.

Call to Action on Herbicide Resistance Management

Management of herbicide resistance can be most effectively accomplished if every person and organization involved in agricultural production takes an ownership position and participates in solving the growing problem of weed resistance to herbicides. Growers and other pest management practitioners are keys to effective herbicide resistance management since they make the final decisions on practices used. However, many other people and organizations have an important role to play as well. Agricultural input supply networks, including chemical companies, are a widely used information source for growers decisions through company marketing efforts. Government agencies may influence decisions through regulations or incentive programs. University scientists through their research, education, and outreach programs may impact management decisions, and organizations such as professional societies, farm and commodity groups, public interest organizations, and the agricultural press play roles as well. It is critically important that all of these groups impacting herbicide resistance management decisions are sending the same message and that message is based on sound science. The time to act is now.

Tropical Soda Apple (Solanum viarum) Herbicide Susceptibility and Competitiveness in Tall Fescue (Festuca arundinacea)1

Abstract:u2009Tropical soda apple (TSA) was evaluated for response to 28 herbicide treatments. Treatments containing picloram or triclopyr controlled eight-leaf, 16-leaf, and 1-yr-old TSA greater than 90% 8 wk after treatment (WAT). Control of 1-yr-old TSA did not increase 8 WAT when triclopyr was mixed in diesel fuel rather than water. In greenhouse additive interference experiments, populations of 0, 1, 2, 4, 8, 16, 32, and 64 TSA plants/700 cm2 of tall fescue had no effect on tall fescue height. TSA height was affected by TSA population, and intraspecific TSA competition was expressed as etiolation at densities greater than 4 plants/700 cm2. Averaged over five periods of competition, predicted yield losses of tall fescue were 14, 16, 29, and 31% and 1, 11, 19, and 23% for 8, 16, 32, and 64 TSA plants/700 cm2, respectively, for each experiment. Differences in tall fescue dry matter response between experiments were attributed to ambient temperature. Dry matter per individual TSA plant decreased from 1.7 to 0.3 g as TSA density increased from 1 to 64 plants/700 cm2. Percent canopy coverage of TSA relative to an area of 700-cm2 surface increased proportionally as tall fescue coverage decreased. After 10 wk of competition, TSA monopolized the canopy with coverage of 92 and 94%; tall fescue coverage was limited to only 7 and 5% in experiments I and II, respectively. Nomenclature: Picloram, 4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid; triclopyr, [(3,5,6-trichloro-2-pyridinyl)oxy]acetic acid; tropical soda apple, Solanum viarum Dunal #3 SOLVI; tall fescue, Festuca arundinacea Schreb. # FESAR ‘Kentucky 31.’ Additional index words: Additive competitive design, chemical control, herbicides, weed density, Solanum khasianum C. B. Clarke var. chatterjeeanum Sengupta, SOLVI. Abbreviations: TSA, tropical soda apple; WAT, weeks after treatment; WATP, weeks after transplanting.

Managing Wicked Herbicide-Resistance: Lessons from the Field

Abstract Herbicide resistance is ‘wicked’ in nature; therefore, results of the many educational efforts to encourage diversification of weed control practices in the United States have been mixed. It is clear that we do not sufficiently understand the totality of the grassroots obstacles, concerns, challenges, and specific solutions needed for varied crop production systems. Weed management issues and solutions vary with such variables as management styles, regions, cropping systems, and available or affordable technologies. Therefore, to help the weed science community better understand the needs and ideas of those directly dealing with herbicide resistance, seven half-day regional listening sessions were held across the United States between December 2016 and April 2017 with groups of diverse stakeholders on the issues and potential solutions for herbicide resistance management. The major goals of the sessions were to gain an understanding of stakeholders and their goals and concerns related to herbicide resistance management, to become familiar with regional differences, and to identify decision maker needs to address herbicide resistance. The messages shared by listening-session participants could be summarized by six themes: we need new herbicides; there is no need for more regulation; there is a need for more education, especially for others who were not present; diversity is hard; the agricultural economy makes it difficult to make changes; and we are aware of herbicide resistance but are managing it. The authors concluded that more work is needed to bring a community-wide, interdisciplinary approach to understanding the complexity of managing weeds within the context of the whole farm operation and for communicating the need to address herbicide resistance.

Implementation of Economic Thresholds for Weeds in Soybean

Herbicide selection for soybean is a complicated task, and consideration of the weed species present, weed density, crop value, potential yield of the field, herbicide and application cost, and the grower’s management style are all necessary in making the best decision. Many growers are now making use of remedial tactics for weed control, including the use of postemergence herbicides. The best use of these remedial treatments is after careful consideration of the potential losses from a weed population compared to the potential economic gain from treatment, or economic thresholds. Field competition studies have been used to develop economic thresholds for weeds in soybean, and these thresholds have been used to create a computerized decision aid for herbicide selection in that crop based on net economic return from the selected treatment. This computer software program (HERBTM) is currently being sold in the U.S., and a similar program for other crops is under development.