Avishek Datta

Dose–Response Curves of Kih-485 for Preemergence Weed Control in Corn

Abstract Field experiments were conducted in Nebraska with the experimental herbicide KIH-485 on soils with three different levels of organic matter (OM) to ascertain a dose response for weed control and corn tolerance. Dose–response curves based on the log-logistic model were used to determine the effective dose that provides 90% weed control (ED90 values) for three grasses (green foxtail, field sandbur, large crabgrass) and two broadleaf weeds (velvetleaf, tall waterhemp). The ED90 values for green foxtail control were 143, 165, and 202 g ai/ha for soils with 1, 2, and 3% OM, respectively at 28 d after treatment (DAT). The highest dose of 371 g ai/ha was needed for field sandbur control at 28 DAT, compared with 141 g ai/ha for large crabgrass, 152 g ai/ha for tall waterhemp, and 199 g ai/ha for velvetleaf. There was no significant corn injury observed. Grain yield increased with increasing doses of KIH-485; optimum yield was achieved at about 195 g ai/ha. From the dose–response curves it is clear that the proposed label rate of KIH-485 of 200 to 300 g ai/ha will provide excellent control of most grasses and certain broadleaf weeds in corn for at least the first 4 wk of the growing season on soils up to 3% OM in the state of Nebraska. Nomenclature: KIH-485 (proposed common name pyrasulfatole), 3-[(5-difluoromethoxy-1-methyl-3-trifluoromethylpyrazol-4-yl)-methylsulfonyl]-4,5-dihydro-5,5-dimethylisoxazole; green foxtail, Setaria viridis (L.) Beauv.; field sandbur, Cenchrus spinifex Cav.; large crabgrass, Digitaria sanguinalis (L.) Scop.; tall waterhemp, Amaranthus tuberculatus (Moq.); velvetleaf, Abutilon theophrasti Medicus; corn, Zea mays L

Growth stage-influenced differential response of foxtail and pigweed species to broadcast flaming.

Abstract Propane flaming could be an effective alternative tool for weed control in organic cropping systems. However, response of major weeds to broadcast flaming must be determined to optimize its proper use. Therefore, field experiments were conducted at the Haskell Agricultural Laboratory, Concord, NE in 2007 and 2008 using six propane doses and four weed species, including green foxtail, yellow foxtail, redroot pigweed, and common waterhemp. Our objective was to describe dose–response curves for weed control with propane. Propane flaming response was evaluated at three different growth stages for each weed species. The propane doses were 0, 12, 31, 50, 68, and 87 kg ha−1. Flaming treatments were applied utilizing a custom-built flamer mounted on a four-wheeler (all-terrain vehicle) moving at a constant speed of 6.4 km h−1. The response of the weed species to propane flaming was evaluated in terms of visual ratings of weed control and dry matter recorded at 14 d after treatment. Weed species response to propane doses were described by log-logistic models relating propane dose to visual ratings or plant dry matter. Overall, response of the weed species to propane flaming varied among species, growth stages, and propane dose. In general, foxtail species were more tolerant than pigweed species. For example, about 85 and 86 kg ha−1 were the calculated doses needed for 90% dry matter reduction in five-leaf green foxtail and four-leaf yellow foxtail compared with significantly lower doses of 68 and 46 kg ha−1 of propane for five-leaf redroot pigweed and common waterhemp, respectively. About 90% dry matter reduction in pigweed species was achieved with propane dose ranging from 40 to 80 kg ha−1, depending on the growth stage when flaming was conducted. A similar dose of 40 to 60 kg ha−1 provided 80% reduction in dry matter for both foxtail species when flaming was done at their vegetative growth stage. However, none of the doses we tested could provide 90% dry matter reduction in foxtail species at flowering stage. It is important to note that foxtail species started regrowing 2 to 3 wk after flaming. Broadcast flaming has potential for control or suppression of weeds in organic farming. Nomenclature: Redroot pigweed, Amaranthus retroflexus L.; common waterhemp, Amaranthus rudis Sauer; green foxtail, Setaria viridis (L.) Beauv.; yellow foxtail, Setaria pumila (Poir.) Roemer and J. A. Schultes.

Adjuvants Influenced Saflufenacil Efficacy on Fall-Emerging Weeds

Abstract Saflufenacil is a new herbicide being developed for preplant burndown and PRE broadleaf weed control in field crops, including corn, soybean, sorghum, and wheat. Field experiments were conducted in 2006 and 2007 at Concord, in northeast Nebraska, with the objective to describe dose–response curves of saflufenacil applied with several adjuvants for broadleaf weed control. Dose–response curves based on log-logistic model were used to determine the effective dose that provides 90% weed control (ED90) values for six broadleaf weeds (field bindweed, prickly lettuce, henbit, shepherds-purse, dandelion, and field pennycress). Addition of adjuvants greatly improved efficacy of saflufenacil. For example, the ED90 values for field bindweed control at 28 d after treatment were 71, 20, 11, and 7 g/ha for saflufenacil applied alone, or with nonionic surfactant (NIS), crop oil concentrate (COC), or methylated seed oil (MSO), respectively. MSO was the adjuvant that provided the greatest enhancement of saflufenacil across all species tested. COC was the second-best adjuvant and provided control similar to MSO on many weed species. NIS provided the least enhancement of saflufenacil. These results are very similar to the proposed label dose of saflufenacil for burndown weed control, which will range from 25 to 100 g/ha with MSO or COC. We believe that such a dose would provide excellent burndown control of most broadleaf weed species that emerge in the fall in Nebraska. Nomenclature: Saflufenacil; dandelion, Taraxacum officinale Weber; field bindweed, Convolvulus arvensis L.; field pennycress, Thlaspi arvense L.; henbit, Lamium amplexicaule L.; prickly lettuce, Lactuca serriola L.; shepherds-purse, Capsella bursa-pastoris (L.) Medik.; corn, Zea mays L.; sorghum, Sorghum bicolor (L.) Moench; soybean, Glycine max L.; wheat, Triticum aestivum L.

Problem weed control in glyphosate-resistant soybean with glyphosate tank mixes and soil-applied herbicides.

Abstract Although glyphosate controls many plant species, certain broadleaf weeds in Nebraskas cropping systems exhibit various levels of tolerance to the labeled rates of this herbicide, including ivyleaf morningglory, Venice mallow, yellow sweetclover, common lambsquarters, velvetleaf, kochia, Russian thistle, and field bindweed. Therefore, two field studies were conducted in 2004 and 2005 at Concord and North Platte, NE, to evaluate performance of (1) seven preemergence (PRE) herbicides and (2) glyphosate tank mixes applied postemergence (POST) at three application times for control of eight weed species that are perceived as problem weeds in glyphosate-resistant soybean in Nebraska. The PRE herbicides, including sulfentrazone plus chlorimuron, pendimethalin plus imazethapyr, imazaquin, and pendimethalin plus imazethapyr plus imazaquin provided more than 85% control of most weed species tested in this study 28 d after treatment (DAT). However, sulfentrazone plus chlorimuron and pendimethalin plus imazethapyr plus imazaquin were the only PRE treatments that provided more than 80% control of most weed species 60 DAT. In the POST glyphosate tank-mix study, the level of weed control was significantly affected by the timing of herbicide application; control generally decreased as weed height increased. In general, glyphosate tank mixes applied at the first two application times (early or mid-POST) with half label rates of lactofen, imazamox, imazethapyr, fomesafen, imazaquin, or acifluorfen, provided more than 80% control of all species that were 20 to 30 cm tall except ivyleaf morningglory, Venice mallow, yellow sweetclover, and field bindweed. Glyphosate tank mixes applied late POST with lactofen, imazethapyr, or imazaquin provided more than 70% control of common lambsquarters, velvetleaf, kochia, and Russian thistle that were 30 to 50 cm tall. Overall, glyphosate tank mixes with half label rates of chlorimuron or acifluorfen were the best treatments; they provided more than 80% control of all the studied weed species when applied at early growth stages. Results of this study suggested that mixing glyphosate with other POST broadleaf herbicides, or utilizing soil-applied herbicides after crop planting helped effectively control most problematic weeds in glyphosate-resistant soybean in Nebraska. Nomenclature: Acifluorfen; chlorimuron; fomesafen; glyphosate; imazamox; imazaquin; imazethapyr; lactofen; pendimethalin; sulfentrazone; common lambsquarters, Chenopodium album L. CHEAL; field bindweed, Convolvulus arvensis L. CONAR; ivyleaf morningglory, Ipomoea hederacea Jacq. IPOHE; kochia, Kochia scoparia (L.) Schrad. KCHSC; Russian thistle, Salsola tragus L. SASKR; velvetleaf, Abutilon theophrasti Medik. ABUTH; Venice mallow, Hibiscus trionum L. HIBTR; yellow sweetclover, Melilotus officinalis (L.) Lam. MEUOF; soybean, Glycine max L.

Flaming as an Alternative Weed Control Method for Conventional and Organic Agronomic Crop Production Systems: A Review

Abstract The interest for organic crop production is in the increase due to a strong demand for organic food from consumers and an attractive income potential for farmers. Weeds pose one of the major problems in crop production and are responsible for significant crop yield reduction. The problem of controlling weeds without synthetic herbicides under the rules of organic agriculture is challenging. The increase in the number of herbicide-resistant weeds, the increase in herbicide cost, and the movement of herbicides into surface and ground water have sparked public awareness and restrictions on herbicide use. For these reasons, weed scientists are considering alternative and integrated weed management practices to reduce herbicide inputs and impacts. The use of propane for flame weeding can be adopted as one of the alternatives to chemical weed control, as it eliminates concerns over direct residual effects on soil, water, and food quality and can lessen the reliance on herbicides, hand weeding, and/or mechanical cultivation. Flame weeding is an acceptable weed control option in both organic and conventional production systems. A greater knowledge on the development of dose–response curves for determining the appropriate propane dose for effective weed control in major agronomic crops is needed to improve flame-weeding strategies. The dose–response curves for weeds and crops are important so that the lowest effective dose of propane can be applied for weed control in agronomic crops, which saves energy and reduces production costs. Depending on the desired level of weed control or tolerable crop injury level, a propane dose could be selected to either control the weed, or reduce its competitive ability against the crop. In this chapter, we will provide an overview of the findings from the flaming research that has been conducted for the last six years at the University of Nebraska, USA, or reported in pertinent newest literature. This chapter will improve our existing knowledge about flame weeding and will present better general guidelines for both organic and conventional crop producers interested in flaming techniques for weed control.

Evaluating the impacts of climate and land-use change on the hydrology and nutrient yield in a transboundary river basin: A case study in the 3S River Basin (Sekong, Sesan, and Srepok)

Assessment of the climate and land-use change impacts on the hydrology and water quality of a river basin is important for the development and management of water resources in the future. The objective of this study was to examine the impact of climate and land-use change on the hydrological regime and nutrient yield from the 3S River Basin (Sekong, Srepok, and Sesan) into the 3S River system in Southeast Asia. The 3S Rivers are important tributaries of the Lower Mekong River, accounting for 16% of its annual flow. This transboundary basin supports the livelihoods of nearly 3.5 million people in the countries of Laos, Vietnam, and Cambodia. To reach a better understanding of the process and fate of pollution (nutrient yield) as well as the hydrological regime, the Soil and Water Assessment Tool (SWAT) was used to simulate water quality and discharge in the 3S River Basin. Future scenarios were developed for three future periods: 2030s (2015-2039), 2060s (2045-2069), and 2090s (2075-2099), using an ensemble of five GCMs (General Circulation Model) simulations: (HadGEM2-AO, CanESM2, IPSL-CM5A-LR, CNRM-CM5, and MPI-ESM-MR), driven by the climate projection for RCPs (Representative Concentration Pathways): RCP4.5 (medium emission) and RCP8.5 (high emission) scenarios, and two land-use change scenarios. The results indicated that the climate in the study area would generally become warmer and wetter under both emission scenarios. Discharge and nutrient yield is predicted to increase in the wet season and decrease in the dry. Overall, the annual discharge and nutrient yield is projected to increase throughout the twenty-first century, suggesting sensitivity in the 3S River Basin to climate and land-use change. The results of this study can assist water resources managers and planners in developing water management strategies for uncertain climate change scenarios in the 3S River Basin.

The Critical Period for Weed Control: Revisiting Data Analysis

There is an ever-larger need for designing an integrated weed management (IWM) program largely because of the increase in glyphosate-resistant weeds, not only in the United States but also worldwide. An IWM program involves a combination of various methods (cultural, mechanical, biological, genetic, and chemical) for effective and economical weed control (Swanton and Weise 1991). One of the first steps in designing an IWM program is to identify the critical period for weed control (CPWC), defined as a period in the crop growth cycle during which weeds must be controlled to prevent crop yield losses (Zimdahl 1988). Knowing the CPWC is useful for making decisions on the need for, and timing of, weed control, depending on the specific crop (Knezevic et al. 2002). CPWC studies have been reported in a variety of crops worldwide, including corn (Zea mays L.) (Evans et al. 2003; Hall et al. 1992), soybean [Glycine max (L.) Merr.] (Knezevic et al. 2003; Van Acker et al. 1993), sunflower (Helianthus annuus L.) (Knezevic et al. 2013), rice (Oryza sativa L.) (Chauhan and Johnson 2011), cotton (Gossypium L. spp.) (Bukun 2004), canola (Brassica napus L.) (Martin et al. 2001), peanut (Arachis hypogaea L.) (Everman et al. 2008), carrot (Daucus carota L.) (Swanton et al. 2010), white bean (Phaseolus vulgaris L.) (Woolley et al. 1993), tomato (Solanum lycopersicum L.) (Weaver and Tan 1983), leek (Allium porrum L.) (Tursun et al. 2007), red pepper (Capsicum annum L.) (Tursun et al. 2012), lentil (Lens culinaris Medik.) (Smitchger et al. 2012), and chickpea (Cicer arietinum L.) (Mohammadi et al. 2005). Several types of data analyses to determine the CPWC have been reported in the literature, including multiple-comparison techniques (Kalaher et al. 2000) and nonlinear regression models (Evans et al. 2003; Van Acker et al. 1993). A nonlinear regression procedure was suggested as a reasonable method for determining the CPWC using SAS software (Knezevic et al. 2002). SAS is powerful software for statistical analysis (SAS Institute 1999); however, because of its licensing requirements, it has not been readily available to the worldwide scientific community. Thus, there has been increased interest in statistical packages that are readily available on the Internet, such as R software (R Development Core Team 2013), which is gaining popularity worldwide. R is open-source, commandline–driven statistical software (similar to SAS) and is free (Knezevic et al. 2007). R can conduct many types of statistical analyses, including various regressions. The user only needs to fit the regression model once and then all parameter combinations of choice can be tested for significance. R also contains sets of prewritten codes (called packages) that are designed to conduct specific types of analysis. One such package is drc (dose–response curves) (Ritz and Streibig 2005). The package drc is an add-on package for the language and environment R and contains programmed commands for regression analysis and enables R to graph the distribution of data and regression lines. Therefore, the objectives of this article are to briefly revisit the concept of, and studies about, the CPWC and to outline a common method for CPWC data analysis based on the sets of codes from the drc package and R software. Adoption of this method of data analysis would allow easier comparison of the results among sites and among researchers.

Integrated Management of Common Reed (Phragmites australis) along the Platte River in Nebraska

Abstract The nonnative biotype of common reed has invaded wetlands in many states including Nebraska, especially along the Platte River from Wyoming to the eastern edge of Nebraska. Therefore, three studies (disking followed by herbicide, mowing followed by herbicide, and herbicide followed by mechanical treatment) were conducted for 3 yr (2008 to 2010) at three locations in Nebraska. The objective was to evaluate common reed control along the Platte River using an integrated management approach based on herbicides (glyphosate or imazapyr), mowing, and disking, either applied alone or in combination. The level of weed control was determined by visual rating, percent flowering, and stem density. On the basis of visual rating, disking and mowing used alone provided common reed control for only a few months. However, the control was significantly prolonged (e.g., at least three seasons) when disking and mowing were combined with herbicide applications. Disking followed by herbicide and mowing followed by herbicide significantly reduced flowering and plant densities (P  =  0.0001) compared to the untreated check. These results suggest that a combination of weed control methods has potential to control common reed. Nomenclature: Imazapyr; glyphosate; common reed, Phragmites australis (Cav.) Trin. ex Steud. subsp. australis PHRCO.

Row spacing impacts the critical period for weed control in cotton (Gossypium hirsutum)

The knowledge on the critical crop-weed competition period is important for designing an efficient weed management program. Field studies were conducted in 2012 and 2013 at the Agricultural Research Institute, Kahramanmaras, Turkey to determine the effects of three row spacing (50, 70 and 90 cm) on the critical period for weed control (CPWC) in cotton. A four parameter logistic equation was fit to data relating relative crop yield to both increasing duration of weed interference and length of weed-free period. The relative yield of cotton was influenced by the duration of weed-infested or weed-free period, regardless of row spacing. In cotton grown at 50 cm row spacing, the CPWC ranged from 117–526 growing degree days (GDD) (V2–V11 growth stages) in 2012 and 124–508 GDD (V2–V10) in 2013 based on the 5% acceptable yield loss level. At 70 cm row spacing, the CPWC ranged from 98–661 GDD in 2012 (V2–V13) and 144–616 GDD (V2–V12) in 2013. At 90 cm row spacing, the CPWC ranged from 80–771 GDD in 2012 (V1–V14) and 83–755 GDD (V1–V14) in 2013. In order to obtain a 95% weed-free yield, the weed management should start at 16 days after crop emergence (DAE) and continued until 52 DAE (V2–V11) for crops grown in 50 cm row spacing, 15 and 60 DAE (V2–V13) for 70 cm row spacing and 11 and 67 DAE (V1–V14) for crops grown in 90 cm row spacing. This suggests that cotton grown in narrow row spacing (50 cm) had greater competiveness against weeds compared with wider row spacing (70 and 90 cm). Cotton growers can benefit from these results by improving cost of weed control through better timing of weed management.

The effects of cultivation methods and water regimes on root systems of drought-tolerant (RD6) and drought-sensitive (RD10) rice varieties of Thailand

ABSTRACT In this study, we have attempted to investigate the effect of different water-saving cultivation techniques on root systems of two Thai rice varieties. The variables were two rice varieties (RD6 and RD10), two cultivation methods (dry direct seeding [DS] and transplanting [TP]) and two soil moisture regimes (field capacity [FC] and 50% FC). RD6 variety had higher root number, root length and root length density compared with RD10 under TP method at FC. Higher root number was observed for TP than dry DS method under FC at flowering stage with 543 and 415 roots plant–1 for RD6 and 392 and 362 roots plant–1 for RD10 cultivated under TP and dry DS methods, respectively. Root dry matter (DM) was the highest for RD6 cultivated through dry DS method compared with TP method at FC for both tillering and flowering stages. RD6 variety resulted in 25% and 50% higher root DM at FC for dry DS than TP at tillering and flowering stages, respectively. The performance of RD10 was poor under 50% FC and dry DS method. With proper selection of variety, dry DS method could be a better alternative for sustainable rice cultivation under water-limited environments.