Delta Research and Extension Center

Tupelo, MS, United States

Delta Research and Extension Center

Tupelo, MS, United States
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Zheljazkov V.D.,Mississippi State University | Astatkie T.,Dalhousie University | Wayne Ebelhar M.,Delta Research and Extension Center
Agronomy Journal | Year: 2010

The commercial production of peppermint (Mentha × piperita L.) is concentrated in more northern latitudes worldwide (north of the 41st parallel), including the United States. This 2-yr field study in Mississippi evaluated the effect of N (0, 80, and 160 kg/ha), growth stage (bud formation and flowering), and harvest time or cut (first cut in mid-July, second cut beginning of October) on peppermint yields, oil content, and composition. Biomass and oil yields were higher from the first cut than from the second. Overall, N increased biomass and oil yields. Contrary to literature reports that peppermint requires long days north of the 41st parallel to reach flowering, peppermint in Mississippi (at 34°43 ́22{double acute accent} N lat) did reach flowering. The average oil yields at bud formation and at flowering were 165 and 122 kg/ha, respectively, and were greater than the average peppermint essential oil yields for the United States in 2008. Generally, (-)-menthol concentration in the oil from the 2007 harvest was lower than in the oil from the 2008 harvest. The average (-)-menthol concentration in the oil from the fertilized plots harvested at flowering in 2008 was 43 to 46%, but (-)-menthol in the other treatments was below 37%. Our results suggest the first harvest in Mississippi should be delayed until the end of July to promote conversion of (-)-menthone to (-)-menthol. Peppermint could provide two harvests per growing season under the Mississippi climate, with oil yields and composition similar to those from other peppermint production regions © 2010 by the American Society of Agronomy.


Riar D.S.,Soil and Environmental science | Norsworthy J.K.,Soil and Environmental science | Steckel L.E.,University of Tennessee | Stephenson IV D.O.,Louisiana State University | And 2 more authors.
Weed Technology | Year: 2013

Soybean consultants from Arkansas, Louisiana, Mississippi, and Tennessee were surveyed by direct mail and by on-farm visits in fall 2011 to assess weed management practices and the prevalence of weed species in midsouth U.S. soybean. These consultants represented 15, 21, 5, and 10% of total soybean planted in Arkansas, Louisiana, Mississippi, and Tennessee, respectively, in 2011. Collectively, 93% of the total scouted area in these four states was planted with glyphosate-resistant (RR) soybean. The adoption of glufosinate-resistant (LL) soybean was greatest in Arkansas (12%), followed by Tennessee (4%), Mississippi (2%), and Louisiana (< 1%). Only 17% of the RR soybean was treated solely with glyphosate, compared with 35% of LL soybean treated solely with glufosinate. Across four states, average cost of herbicides in RR and LL soybean systems was US$78 and US$91 ha-1, respectively. Collectively across states, total scouted area under conventional tillage was 42%, stale seedbed was 37%, and no-tillage was 21%. Palmer amaranth and morningglories were the most problematic weeds in all four states. Additionally, barnyardgrass and horseweed were the third most problematic weeds of Arkansas and Tennessee, respectively, and Italian ryegrass was the third most problematic weed in Louisiana and Mississippi. Glyphosate-resistant Palmer amaranth infested fewer fields in Louisiana (16% of fields) than it did in the remaining three states (54% collectively). Average Palmer amaranth hand-weeding costs in the midsouth was US$59 ha-1. Three-fourths of the midsouth consultants stipulated the need for continued research and education focused on management of glyphosate-resistant and glyphosate-tolerant weed species.


Riar D.S.,Soil and Environmental science | Norsworthy J.K.,Soil and Environmental science | Steckel L.E.,University of Tennessee | Stephenson D.O.,Research Station | And 3 more authors.
Weed Technology | Year: 2013

In fall 2011, cotton and soybean consultants from Arkansas, Louisiana, Mississippi, and Tennessee were surveyed through direct mail and on-farm visits, and rice consultants from Arkansas and Mississippi were surveyed through direct mail to assess the importance and level of implementation of herbicide resistance best management practices (HR-BMPs) for herbicide-resistant weeds. Proper herbicide timing, clean start with no weeds at planting, application of multiple effective herbicide modes of action, use of full labeled herbicide rates, and prevention of crop weed seed production with importance rating of ≥ 4.6 out of 5.0 were perceived as the most important HR-BMPs in all crops. Purchase of certified rice seed was on 90% of scouted hectares. In contrast, least important HR-BMPs as perceived by consultants with importance ratings of ≤ 4.0 in cotton, ≤ 3.7 in rice, and ≤ 3.8 in soybean were cultural practices such as manual removal of weeds; tillage including disking, cultivation, or deep tillage; narrow (≤ 50 cm)-row crops, cover crops, and altered planting dates. Narrow crop rows and cover crops in cotton; altered planting dates in cotton and soybean; and cleaning of farm equipment and manual weeding in rice and soybean is currently employed on ≤ 20% of scouted hectares. Extra costs, time constraints, adverse weather conditions, lack of labor and equipment, profitability, herbicide-related concerns, and complacency were perceived as key obstacles for adoption of most HR-BMPs. With limited adoption of most cultural practices that reduce risks of herbicide-resistant weeds, there are opportunities to educate growers concerning the proactive need and long-term benefits of adopting HR-BMPs to ensure sustainable weed management and profitable crop production.


Riar D.S.,Soil and Environmental science | Norsworthy J.K.,Soil and Environmental science | Steckel L.E.,University of Tennessee | Stephenson IV D.O.,Research Station | Bond J.A.,Delta Research and Extension Center
Weed Technology | Year: 2013

A survey questionnaire was sent to cotton consultants of Arkansas and Mississippi through direct mail and Louisiana and Tennessee consultants through on-farm visits in fall of 2011. The survey was returned by a total of 22 Arkansas, 17 Louisiana, 10 Mississippi, and 11 Tennessee cotton consultants, representing 26, 53, 13, and 38% of total cotton planted in these states in 2011, respectively. Collectively, the area planted to glyphosate-resistant (Roundup Ready®, RR) cotton was 97%, glyphosate plus glufosinate-resistant (Widestrike® Flex, WRF) cotton was 30%, and glufosinate-resistant (Liberty Link, LL) cotton was 2.6% of the total cotton surveyed in 2011. Seventy percent of area in all states is still under continuous RR/WRF cotton. Average cost of herbicides in RR systems was $ 114 ha-1 and in LL systems was $137 ha-1. Across the states, cotton planted under no-tillage, conservation tillage, and conventional tillage was 31, 36, and 33%, respectively, of total scouted cotton. Area under conventional tillage increased and conservation tillage decreased in Arkansas compared with a previous survey conducted in 2006. Palmer amaranth, morningglories, and horseweed in the order of listing were the most problematic weeds of cotton across Arkansas, Mississippi, and Tennessee. In Louisiana, however, morningglories were the most problematic weed followed by Palmer amaranth and common waterhemp. Glyphosate-resistant (GR) Palmer amaranth infested only 13% of scouted cotton area in Louisiana compared with 75% in the remaining three states, and consequently, hand-weeding to control GR Palmer amaranth is practiced on only 2.5% of total scouted area of Louisiana and 49% of the scouted area of the remaining three states. Hand-weeding added an additional $12 to 371 ha-1 to weed-management costs. One-half (50%) of the cotton consultants emphasized the need for more research on residual herbicides that can control GR Palmer amaranth effectively.


Spindel J.,Cornell University | Begum H.,International Rice Research Institute | Akdemir D.,Cornell University | Virk P.,International Center for Tropical Agriculture | And 7 more authors.
PLoS Genetics | Year: 2015

Genomic Selection (GS) is a new breeding method in which genome-wide markers are used to predict the breeding value of individuals in a breeding population. GS has been shown to improve breeding efficiency in dairy cattle and several crop plant species, and here we evaluate for the first time its efficacy for breeding inbred lines of rice. We performed a genome-wide association study (GWAS) in conjunction with five-fold GS cross-validation on a population of 363 elite breeding lines from the International Rice Research Institute's (IRRI) irrigated rice breeding program and herein report the GS results. The population was genotyped with 73,147 markers using genotyping-by-sequencing. The training population, statistical method used to build the GS model, number of markers, and trait were varied to determine their effect on prediction accuracy. For all three traits, genomic prediction models outperformed prediction based on pedigree records alone. Prediction accuracies ranged from 0.31 and 0.34 for grain yield and plant height to 0.63 for flowering time. Analyses using subsets of the full marker set suggest that using one marker every 0.2 cM is sufficient for genomic selection in this collection of rice breeding materials. RR-BLUP was the best performing statistical method for grain yield where no large effect QTL were detected by GWAS, while for flowering time, where a single very large effect QTL was detected, the non-GS multiple linear regression method outperformed GS models. For plant height, in which four mid-sized QTL were identified by GWAS, random forest produced the most consistently accurate GS models. Our results suggest that GS, informed by GWAS interpretations of genetic architecture and population structure, could become an effective tool for increasing the efficiency of rice breeding as the costs of genotyping continue to decline.


Mundt C.C.,Oregon State University | Wallace L.D.,Oregon State University | Allen T.W.,Delta Research and Extension Center | Hollier C.A.,Louisiana State University | And 2 more authors.
Biological Invasions | Year: 2013

Hosts of soybean rust (Phakopsora pachyrhizi) are sensitive to low temperatures, limiting this obligate parasite in the United States to overwintering sites in a restricted area along the Gulf Coast. This temperature sensitivity of soybean rust hosts allowed us to study spatial spread of epidemic invasions over similar territory for seven sequential years, 2005-2011. The epidemic front expanded slowly from early April through July, with the majority of expansion occurring from August through November. There was a 7.4-fold range of final epidemic extent (0.4-3.0 million km2) from the year of smallest final disease extent (2011) to that of the largest (2007). The final epidemic area of each year was regressed against epidemic areas recorded at one-week intervals to determine the association of final epidemic extent with current epidemic extent. Coefficients of determination for these regressions varied between 0.44 and 0.62 during April and May. The correlation coefficients varied between 0.70 and 0.96 from early June through October, and then increased monotonically to 1.0 by year's end. Thus, the spatial extent of disease when the epidemics began rapid expansion may have been a crucial contributor to subsequent spread of soybean rust. Our analyses used presence/absence data at the county level to evaluate the spread of the epidemic front only; the subsequent local intensification of disease could be strongly influenced by other factors, including weather. © 2012 Springer Science+Business Media Dordrecht.


Hensley J.B.,Louisiana State University | Webster E.P.,Louisiana State University | Blouin D.C.,Louisiana State University | Harrell D.L.,Louisiana State University | Bond J.A.,Delta Research and Extension Center
Weed Technology | Year: 2013

Field studies were conducted near Crowley, LA in 2005 through 2007 to evaluate the effects of simulated herbicide drift on 'Cocodrie' rice. Each application was made with the spray volume varying proportionally to herbicide dosage based on a constant spray volume of 234 L ha-1 and a glyphosate rate of 863 g ae ha-1. The 6.3%, 54-g ha-1, herbicide rate was applied at a spray volume of 15 L ha-1, and the 12.5%, 108-g ha-1, herbicide rate was applied at a spray volume of 29 L ha-1. Compared with the nontreated, glyphosate applied at one tiller, panicle differentiation (PD), and boot resulted in increased crop injury. The greatest injury was observed on rice treated at the one-tiller timing. Applications of glyphosate at one tiller, PD, and boot reduced plant height at harvest and primary and total crop yield. Rice treated at primary crop maturity was not affected by glyphosate applications.


Carlson T.P.,Louisiana State University | Webster E.P.,Louisiana State University | Salassi M.E.,Louisiana State University | Bond J.A.,Delta Research and Extension Center | And 2 more authors.
Weed Technology | Year: 2012

Field studies were conducted in Crowley, LA, and Stoneville, MS, in drill-seeded rice to evaluate economical returns of weed control with imazethapyr. Red rice and barnyardgrass control was evaluated with imazethapyr alone at various rates and application timings. Imazethapyr, averaged across rate, controlled red rice 89% and barnyardgrass 90% when the initial application of imazethapyr was applied at emergence followed by a second application of imazethapyr 2 wk later. No difference in red rice and barnyardgrass control was observed with imazethapyr, averaged across timing. Yield and economical returns were maximized when the initial application of imazethapyr was applied at rice emergence followed by a second application of imazethapyr 2 wk later. © 2012 Weed Science Society of America.


Hensley J.B.,Louisiana State University | Webster E.P.,Louisiana State University | Blouin D.C.,Louisiana State University | Harrell D.L.,Louisiana State University | Bond J.A.,Delta Research and Extension Center
Weed Technology | Year: 2012

Field studies were conducted near Crowley, LA, in 2005 through 2007 to evaluate the effects of simulated herbicide drift on 'Cocodrie' rice. Each application was made with the spray volume varying proportionally to herbicide dosage based on a constant spray volume of 234 L ha-1 and an imazethapyr rate of 70 g ai ha-1. The 6.3, 4.4 g ha-1, herbicide rate was applied at a spray volume of 15 L ha-1 and the 12.5, 8.7 g ha-1, herbicide rate was applied at a spray volume of 29 L ha-1. An application of imazethapyr at one-tiller, panicle differentiation (PD), and boot resulted in increased crop injury compared with the nontreated rice. The most injury observed occurred on rice treated at the one-tiller timing. Imazethapyr at one-tiller, PD, and boot reduced plant height at harvest and primary and total (primary plus ratoon) crop yield, with the greatest reduction in primary crop yield resulting from imazethapyr applied at boot. Imazethapyr did not affect rice treated at primary crop maturity.


Riar D.S.,Dow AgroSciences | Tehranchian P.,University of Arkansas | Norsworthy J.K.,University of Arkansas | Nandula V.,U.S. Department of Agriculture | And 5 more authors.
Weed Science | Year: 2015

Overuse of acetolactate synthase (ALS)-inhibiting herbicides in rice has led to the evolution of halosulfuron-resistant rice flatsedge in Arkansas and Mississippi. Resistant accessions were cross-resistant to labeled field rates of ALS-inhibiting herbicides from four different families, in comparison to a susceptible (SUS) biotype. Resistance index of Arkansas and Mississippi accessions based on an R/S ratio of the lethal dose required for 50% plant mortality (LD50) to bispyribac-sodium, halosulfuron, imazamox, and penoxsulam was ≥21-fold. Control of Arkansas, Mississippi, and SUS accessions with labeled field rates of 2,4-D, bentazon, and propanil was ≥93%. An enzyme assay revealed that an R/S ratio for 50% inhibition (I50) of ALS for halosulfuron was 2,600 and 200 in Arkansas and Mississippi, respectively. Malathion studies did not reveal enhanced herbicide metabolism in resistant plants. The ALS enzyme assay and cross-resistance studies point toward altered a target site as the potential mechanism of resistance. Trp574-Leu amino acid substitution within the ALS gene was found in both Arkansas and Mississippi rice flatsedge accessions using the Illumina HiSeq platform, which corresponds to the mechanism of resistance found in many weed species. Field-rate applications of 2,4-D, bentazon, and propanil can be used to control these ALS-resistant rice flatsedge accessions. © 2015 Weed Science Society of America.

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