Ramon G. Leon

Effect of temperature on the germination of common waterhemp (Amaranthus tuberculatus), giant foxtail (Setaria faberi), and velvetleaf (Abutilon theophrasti)

Abstract Common waterhemp, giant foxtail, and velvetleaf seed germination in response to temperature was studied with a two-way thermogradient plate. Seeds were maintained under dark and wet conditions at 4 C for 12 wk, and velvetleaf seeds were scarified before the experiments were conducted. The seeds were germinated at 25 different temperature treatments. Minimum and optimum temperatures for velvetleaf germination were approximately 8 and 24 C, respectively. Temperature alternation did not affect the germination of this species. The minimum germination temperature was 10 C for common waterhemp and 14 C for giant foxtail. The optimum germination of giant foxtail occurred at approximately 24 C, but common waterhemp optimum germination was variable depending on temperature alternation. Increased amplitude of the diurnal temperature alternation increased percent germination of these two species, and this was more evident at lower temperatures. In the case of common waterhemp, the temperature required to reach specific germination percentages was reduced by increasing the amplitude of the temperature alternation. Nomenclature: Common waterhemp, Amaranthus tuberculatus (Moq.) J.D. Sauer. synonymous Amaranthus rudis J.D. Sauer. AMATA; giant foxtail, Setaria faberi Herrm. SETFA; velvetleaf, Abutilon theophrasti Medicus. ABUTH.

Regulation of weed seed dormancy through light and temperature interactions

Abstract The effects of temperature and light on the dormancy of velvetleaf, common waterhemp, and giant foxtail seeds were studied under controlled growth chamber conditions. Seeds were either kept chilled at 4 C for 12 wk under wet conditions or nonchilled at 4 C in dry storage. Then, seeds were germinated under increasing and decreasing temperatures and under continuous red light (R) and far-red light (FR). In addition, chilled and nonchilled seeds were germinated in the dark after being exposed to alternating R and FR flashes. Velvetleaf germination was increased by exposure to high temperatures (36 C) immediately after exposure to low temperatures (4 C), but light had no effect. Chilling increased common waterhemp seed germination and sensitivity to light and temperature. R promoted common waterhemp seed germination, whereas FR inhibited germination and maintained dormancy. In addition, the effect of light was reversible. Therefore, common waterhemp dormancy was phytochrome regulated. However, high temperatures (36 C) promoted the germination of chilled seeds, even when exposed to FR. The germination of chilled giant foxtail seeds was reduced by FR. Giant foxtail seed dormancy was partially phytochrome regulated, but dormancy regulation was more dependent on mean temperature. Nomenclature: Common waterhemp, Amaranthus tuberculatus (Moq.) J.D. Sauer. syn. Amaranthus rudis Sauer. AMATA; giant foxtail, Setaria faberi Herrm. SETFA; velvetleaf, Abutilon theophrasti Medicus. ABUTH.

Artificial and natural seed banks differ in seedling emergence patterns

Abstract Artificial weed seed banks are practical for studying seed bank depletion and weed seedling emergence because the number, depth, and species composition of seed banks can be managed. However, no studies have determined whether artificial seed banks are representative of natural seed banks. We compared the emergence of velvetleaf, giant foxtail, and common waterhemp in a natural seed bank, an artificial seed bank with stratified seeds, and an artificial seed bank with nonstratified seeds. Velvetleaf seedling emergence was higher in the nonstratified seed bank in 2001, but no differences were observed in 2002. The number of viable velvetleaf seeds at the end of the experiment was lower in the natural seed bank than in the artificial seed banks in 2002. Velvetleaf emergence occurred earlier in the natural seed bank than in the artificial seed banks. Giant foxtail emergence was higher in the artificial seed banks (58 to 82%) than in the natural seed bank (5 to 23%). Common waterhemp emergence ranged from 7 to 65% in the artificial seed banks and from 1 to 5% in the natural seed bank. In general, the distribution of emergence with time differed in the natural seed bank compared with the artificial seed banks. These differences were attributed to differences in soil temperature and soil bulk density between the natural and artificial seed banks. Artificial seed banks showed lower soil bulk density and greater temperature fluctuation than the natural seed bank. However, there was no consistent relationship between growing degree days and emergence timing in the three treatments for any of the species studied. Nomenclature: Common waterhemp, Amaranthus tuberculatus (Moq.) J.D. Sauer. synonymous Amaranthus rudis J.D. Sauer. AMATA; giant foxtail, Setaria faberi Herrm. SETFA; velvetleaf, Abutilon theophrasti Medicus. ABUTH.

Impact of Weed Management Practices on Grapevine Growth and Yield Components

Abstract The need for reducing costs and making grape production more sustainable has prompted the search for alternative weed control practices that optimize production while maintaining profits. For this reason, it is imperative to understand how different weed management practices modify vine–weed interactions. In the present study, we evaluated the effect on weed growth and Zinfandel grapevine growth and production of five weed control practices: (1) flumioxazin, (2) simazine, (3) cultivation, (4) cover crop, and (5) untreated control. The herbicide treatments had the lowest weed biomass, followed by the cultivation, being approximately 10 and 2 times lower than the weed biomass of either the cover crop or untreated control treatments, respectively. However, the differences in grape yield were not as evident. In 2006, a rainy year, the herbicides and cultivation treatments did not differ in grape yield, but the cover crop and untreated control had a reduction of approximately 20% compared with the other treatments. In 2007, a dry year, in comparison to the herbicide treatments, the grape yield reductions of cultivation were around 22%, and those of the cover crop and untreated control were around 48%. Although the cover crop reduced grape yield, it suppressed weed species considered important, such as horseweed, panicle willowherb, scarlet pimpernel, and sowthistle. Also, it was concluded that vines can tolerate a certain amount of weed competition, and that properly timed postemergence control actions (e.g., cultivation or POST herbicides) could provide the necessary level of control to obtain the desired yields. However, under limited soil moisture conditions, the use of PRE herbicides could prove important to maintain vine yield and vigor. Nomenclature: Flumioxazin; simazine; horseweed, Conyza canadensis (L.) Cronq.; panicle willowherb, Epilobium brachycarpum K. Presl.; scarlet pimpernel, Anagallis arvensis L.; sowthistle, Sonchus sp. L.; grape, Vitis vinifera L

Impact of Exposure to 2,4-D and Dicamba on Peanut Injury and Yield

Abstract The potential widespread adoption of cotton and soybean varieties with 2,4-D and dicamba resistance traits in the southeastern US will increase the risk of accidental exposure of peanut to these herbicides because of drift or application errors. When such accidents occur, growers must decide between continuing the crop and terminating it. In order to make this decision, growers need to estimate the potential yield reduction caused by 2,4-D or dicamba. Dose-response studies were conducted under field conditions in Citra and Jay, FL in 2012 and 2013 to determine peanut injury and yield reduction after exposure to 70, 140, 280, 560, and 1120 g ae ha−1 of 2,4-D or to 35, 70, 140, 280, and 560 g ae ha−1 of dicamba at 21 and 42 d after planting (DAP). Only herbicide by rate interactions were significant (P < 0.04). Dicamba caused 2 to 5 times higher peanut injury and 0.5 to 2 times higher yield reductions than 2,4-D. Injury ranged from 0 to 35% when peanut plants were treated with 2,4-D and from 20 to 78% with dicamba. The maximum yield reduction was 41% with 1,120 g ha−1 of 2,4-D and 65% with 560 g ha−1 of dicamba. Linear regression indicated that the intercept for yield reduction was 12% for 2,4-D and 23% for dicamba, and there was a 2.5% and 7.7% increase in yield reduction per additional 100 g ha−1, respectively. Although high variability was observed for the different variables, there was a positive correlation between injury and peanut yield reduction (P < 0.0001) with Pearsons Rho values ranging from 0.45 to 0.59 for 2,4-D and from 0.27 to 0.55 for dicamba, suggesting that growers can use injury data to make rough projections of yield reduction and decide if they continue their crop, especially when injury is evident. Nomenclature: 2,4-D; dicamba; peanut; Arachis hypogaea L. Resumen La amplia adopción potencial de variedades de algodón y soya con resistencia a 2,4-D y dicamba en el sureste de los Estados Unidos aumentará el riesgo en maní de exposición accidental a estos herbicidas debido a deriva o errores de aplicación. Cuando estos accidentes ocurran, los productores deberán decidir entre continuar con el cultivo o terminarlo. Para tomar esta decisión, los productores necesitan estimar el potencial de reducción del rendimiento a causa de 2,4-D o dicamba. Se realizaron estudios de respuesta a dosis bajo condiciones de campo en Citra y Jay, FL en 2012 y 2013 para determinar el daño y reducción de rendimiento en el maní después de la exposición a 70, 140, 280, 560 y 1120 g ae ha−1 de 2,4-D o a 35, 70, 140, 280, y 560 g ae ha−1 de dicamba a 21 y 42 d después de la siembra (DAP). Solamente interacciones entre el herbicida y la dosis fueron significativas (P<0.04). Dicamba causó de 2 a 5 veces mayor daño al maní y de 0.5 a 2 veces mayor reducción en el rendimiento que 2,4-D. La mayor reducción del rendimiento fue 41% con 1,120 g ha−1 de 2,4-D y 65% con 560 g ha−1 de dicamba. Regresiones lineales indicaron que el intercepto para la reducción del rendimiento fue 12% para 2,4-D y 23% para dicamba, y hubo un incremento de 2.5% y 7.7% en la pérdida de rendimiento por cada 100 g ha−1 adicionales de estos herbicidas, respectivamente. Aunque se observó una alta variabilidad para las diferentes variables, hubo una correlación positiva entre el daño y la reducción en el rendimiento del maní (P<0.0001) con valores de Rho de Pearson de 0.45 a 0.59 para 2,4-D y 0.27 a 0.55 para dicamba, lo que sugiere que los productores pueden usar datos de daño para hacer proyecciones aproximadas de pérdida de rendimiento y así decidir si continúan el cultivo, especialmente cuando el daño es evidente.

Interspecific Differences in Weed Susceptibility to Steam Injury

Abstract Thermal weed control methods have been incorporated into weed control programs in organic and conventional production systems. Flaming is commonly used, but steaming has been proposed to increase efficiency of heat transfer to weeds and reduce the risk of fire. The objective of this research was to measure injury to leaves of plant species that differ in leaf morphology and to measure injury to plants at different stages of plant development. The study was conducted in a glasshouse and plants were exposed to steaming at 400 C for 0.36 s—equivalent to a steaming speed of 2 km/h. Overall, leaf thickness was the best morphological characteristic to predict injury (r2  =  0.51), with greater thickness resulting in less injury. For broadleaf species only, species with wider leaves were injured more than species with narrower leaves (r2  =  0.64). Injury was greatest when plants had fewer than six true leaves and when their shoots were less than 10 cm long. There was a wide range of injury across species, and the grass species bermudagrass and perennial ryegrass were injured (68 to 81%) more than other species such as common purslane and English daisy (23 to 34%). Biomass of all species tested was reduced by approximately 40%, indicating that leaf injury was not the sole effect of steaming on plant growth. These results indicated that considering both visual estimates of injury and morphological characteristics is important to properly assess thermal weed control effectiveness. Nomenclature: Bermudagrass, Cynodon dactylon (L.) Pers.; common purslane, Portulaca oleracea L.; English daisy, Bellis perennis L.; perennial ryegrass, Lolium perenne L

Technology for Automation of Weed Control in Specialty Crops

Specialty crops, like flowers, herbs, and vegetables, generally do not have an adequate spectrum of herbicide chemistries to control weeds and have been dependent on hand weeding to achieve commercially acceptable weed control. However, labor shortages have led to higher costs for hand weeding. There is a need to develop labor-saving technologies for weed control in specialty crops if production costs are to be contained. Machine vision technology, together with data processors, have been developed to enable commercial machines to recognize crop row patterns and control automated devices that perform tasks such as removal of intrarow weeds, as well as to thin crops to desired stands. The commercial machine vision systems depend upon a size difference between the crops and weeds and/or the regular crop row pattern to enable the system to recognize crop plants and control surrounding weeds. However, where weeds are large or the weed population is very dense, then current machine vision systems cannot effectively differentiate weeds from crops. Commercially available automated weeders and thinners today depend upon cultivators or directed sprayers to control weeds. Weed control actuators on future models may use abrasion with sand blown in an air stream or heating with flaming devices to kill weeds. Future weed control strategies will likely require adaptation of the crops to automated weed removal equipment. One example would be changes in crop row patterns and spacing to facilitate cultivation in two directions. Chemical company consolidation continues to reduce the number of companies searching for new herbicides; increasing costs to develop new herbicides and price competition from existing products suggest that the downward trend in new herbicide development will continue. In contrast, automated weed removal equipment continues to improve and become more effective.

Biochar Decreases Atrazine and Pendimethalin Preemergence Herbicidal Activity

Abstract Biochar and vinasse are by-products of biofuel production that can be used as soil amendments. However, their addition to the soil might affect PRE herbicide activity. Although studies have shown that biochar has a high herbicide adsorption capacity, there is little information available about biochar effect on weed control especially under field conditions. Therefore, the objective of this study was to determine the influence of biochar and vinasse application on atrazine and pendimethalin availability and herbicide activity under in vitro and field conditions. In vitro atrazine and pendimethalin herbicidal activities were not influenced by vinasse addition, but biochar application reduced atrazine and pendimethalin injury for all evaluated species. A sorption experiment confirmed high affinity of biochar for atrazine and pendimethalin. Linear regression analysis showed that the slope for atrazine and pendimethalin adsorption was 16 and 4 times higher in soil with biochar than in soil alone. Under field conditions, biochar at 0.5 kg m−2 reduced atrazine and pendimethalin weed control 75% and 60%, respectively. These results suggested that the use of biochar as a soil amendment in cropping system could decrease PRE herbicide efficacy. Therefore, mitigating practices such as the use of higher rates or reliance on POST herbicides and cultivation might be necessary to ensure proper weed control. Nomenclature: Atrazine; pendimethalin; biochar; vinasse. Resumen El biochar y la vinaza son subproductos de la producción de biocombustibles que pueden ser usados como enmiendas de suelo. Sin embargo, su adición al suelo podría afectar la actividad de herbicidas PRE. Aunque estudios han mostrado que el biochar tiene una alta capacidad de adsorción de herbicidas, hay poca información disponible acerca del efecto del biochar sobre el control de malezas, especialmente bajo condiciones de campo. Por esta razón, el objetivo de este estudio fue determinar la influencia de la aplicación de biochar y de vinaza sobre la disponibilidad y actividad herbicida de atrazine y pendimethalin in vitro y en condiciones de campo. In vitro, la actividad herbicida de atrazine y pendimethalin no fue influenciada por la adición de vinaza, pero la aplicación de biochar redujo el daño causado por atrazine y pendimethalin en todas las especies evaluadas. Un experimento de sorción confirmó la alta afinidad del biochar por atrazine y pendimethalin. Análisis de regresión lineal mostraron que las pendientes de las curvas de adsorción de atrazine y pendimethalin fueron 16 y 4 veces mayores en suelo con biochar que en suelo solo. Bajo condiciones de campo, el biochar a 0.5 kg m−2 redujo el control de malezas de atrazine y pendimethalin en 75% y 60%, respectivamente. Estos resultados sugirieron que el uso de biochar como enmienda de suelo en sistemas de cultivos podría disminuir la eficacia de herbicidas PRE. Por esto, prácticas de mitigación tales como el uso de mayores dosis o una mayor dependencia en herbicidas POST y labranza podrían ser necesarios para asegurar un control adecuado de malezas.

Weed Seed Banks Are More Dynamic in a Sod-Based, Than in a Conventional, Peanut-Cotton Rotation

Abstract Crop rotation promotes productivity, nutrient cycling, and effective pest management. However, in row-crop systems, rotation is frequently limited to two crops. Adding a third crop, especially a perennial crop, might increase crop-rotation benefits, but concerns about disruption of agricultural and ecological processes preclude grower adoption of a three-crop rotation. The objective of the present research was to determine whether weed seed banks differ between a sod-based rotation (bahiagrass–bahiagrass–peanut–cotton) and a conventional peanut–cotton rotation (peanut–cotton–cotton) and the importance of crop phase in weed seed-bank dynamics in a long-term experiment initiated in 1999 in Florida. Extractable (ESB) and germinable (GSB) seed banks were evaluated at the end of each crop phase in 2012 and 2013, and total weed seed or seedling number, Shannon-Weiner’s diversity (H′), richness, and evenness were determined. ESB increased in H′ (36%), richness (29%), and total number of weed seeds (40%) for sod-based compared with conventional rotation, whereas GSB increased 32% in H′, 27% in richness, and 177% in total number of weed seedlings. Crop phase was a determinant factor in the differences between crop rotations. The first year of bahiagrass (B1) exhibited increases in weed seed and seedling number, H′, and richness and had the highest values observed in the sod-based rotation. These increases were transient, and in the second year of bahiagrass (B2), weed numbers and H′ decreased and reached levels equivalent to those in the conventional peanut–cotton rotation. The B1 phase increased the germinable fraction of the seed bank, compared with the other crop phases, but not the total number of weed seeds as determined by ESB. The increases in H′ and richness in bahiagrass phases were mainly due to grass weed species. However, these grass weed species were not associated with peanut and cotton phases of the sod-based rotation. The results of the present study demonstrated that including bahiagrass as a third crop in a peanut–cotton rotation could increase weed community diversity, mainly by favoring increases in richness and diversity, but the structure and characteristics of the rotation would prevent continuous increases in the weed seed bank that could affect the peanut and cotton phases. Nomenclature: Bahiagrass, Paspalum notatum Fluegg; cotton, Gossypium hirsutum L.; peanut, Arachis hypogaea L.

Using choice experiments to understand household tradeoffs regarding pineapple production and environmental management in Costa Rica

Choices among environmental management alternatives involve tradeoffs where, for example, the benefits of environmental protection may be offset by economic costs or welfare losses to individual agents. Understanding individual or household-level preferences regarding these tradeoffs is not always straightforward, and it often requires an analysis of choices under alternative scenarios. A household survey was used to gather data for a choice experiment, where respondents were asked to choose among pairs of alternative management scenarios about pineapple production in Costa Rica. The experimental design consisted of six attributes that varied on between two and five attribute levels, and the experiment and accompanying survey were administered orally in Spanish. The results show that respondents are willing to make tradeoffs with respect to the management attributes in order to see an overall improvement in environmental quality. Respondents were willing to accept a moderate level of pesticide application, presumably in exchange for paying a lower cost or seeing a gain in another area, such as monitoring or soil conservation. Buffer zones were significant only in the case of large farms. The results have implications for policy decisions that aim to reflect public attitudes, particularly the aspects of pineapple production that matter most to people living near pineapple plantations. The study also highlights the effectiveness of the choice experiment approach in examining household preferences about environmental management in a rural development context.