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Dive into the research topics where Forrest Mitchell is active.

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Featured researches published by Forrest Mitchell.


Plant Disease | 2003

Serratia marcescens, a phloem-colonizing, squash bug-transmitted bacterium: causal agent of cucurbit yellow vine disease.

B. D. Bruton; Forrest Mitchell; Jacqueline Fletcher; S. D. Pair; Astri Wayadande; Ulrich Melcher; J. Brady; Blake R. Bextine; T. W. Popham

Cucurbit yellow vine disease (CYVD), which can inflict heavy losses to watermelon, pumpkin, cantaloupe, and squash in U.S. production areas from the midwest to northeastern states, causes phloem discoloration, foliar yellowing, wilting, and plant decline. Bacteria were cultured from the phloem of crown sections of symptomatic plants of Citrullus lanatas and Cucurbita pepo. Those bacteria testing positive in CYVD-specific polymerase chain reaction (PCR) were all gram negative and appeared morphologically identical, producing creamy white, smooth, entire, convex colonies on Luria-Bertani or nutrient agar. Characterized cucurbit-derived strains of Serratia marcescens were introduced into greenhouse-grown squash plants by puncture inoculation and into field-grown squash plants by enclosure with S. marcescens-fed squash bugs, Anasa tristis. Up to 60% of the bacteria-inoculated plants in the greenhouse and up to 17% of field plants caged with inoculative squash bugs developed phloem discoloration and tested positive for S. marcescens by CYVD-specific PCR. None of the controls developed phloem discoloration or tested positive by PCR. Of the diseased field plants, 12% (2 of 35) also yellowed, wilted, and collapsed, exhibiting full symptom development of CYVD. However, neither plant collapse nor decline was observed in the greenhouse-grown, puncture-inoculated plants. The morphology, growth habit, and PCR reaction of bacteria cultured from crown tissue of a subset of plants in each experimental group were indistinguishable from those of the inoculum bacteria. Evidence presented from our studies confirms that the squash bug can transmit S. marcescens, the CYVD causal bacterium. The S. marcescens-A. tristis relationship described here is the first instance in which the squash bug has been identified as a vector of a plant pathogen. Our experiments represent a completion of the steps of Kochs postulates, demonstrating that S. marcescens is the causal agent of CYVD and that the squash bug, A. tristis, is a vector of the pathogen.


Journal of Environmental Science and Health Part B-pesticides Food Contaminants and Agricultural Wastes | 2013

Time dependent sorption behavior of dinotefuran, imidacloprid and thiamethoxam

Sudarshan Kurwadkar; Dustan Dewinne; Remington Wheat; Donald G. McGahan; Forrest Mitchell

Dinetofuran (DNT), imidacloprid (IMD) and thiamethoxam (THM) are among the neonicotinoid insecticides widely used for managing insect pests of agricultural and veterinary importance. Environmental occurrence of neonicotinoid in post-application scenario poses unknown issues to human health and ecology. A sorption kinetic study provides much needed information on physico-chemical interaction of neonicotinoid with soil material. In this research study, time-dependent sorption behavior of DNT, IMD and THM in vineyard soil was studied. Sorption kinetics studies were conducted over a period of 96 hours with sampling duration varying from 0, 2, 4, 8, 12, 24, 60 and 96 hours. All three neonicotinoids exhibited very low sorption potential for the soil investigated. Overall percent sorption for all three neonicotinoids was below 20.04 ± 2.03% with highest percent sorption being observed for IMD followed by DNT and THM. All three neonicotinoids are highly soluble with solubility increasing with IMD < THM < DNT. Although, DNT has the highest solubility among all three neonicotinoids investigated, it exhibited higher percent sorption compared to THM, indicating factors other than solubility influenced the sorption kinetics. Low sorption potential of neonicotinoids indicates greater leaching potential with regard to groundwater and surface water contamination.


Journal of Contaminant Hydrology | 2014

Evaluation of leaching potential of three systemic neonicotinoid insecticides in vineyard soil.

Sudarshan Kurwadkar; Remington Wheat; Donald G. McGahan; Forrest Mitchell

Dinotefuran (DNT), imidacloprid (IMD), and thiamethoxam (THM) are commonly used neonicotinoid insecticides in a variety of agriculture operations. Although these insecticides help growers control pest infestation, the residual environmental occurrence of insecticides may cause unintended adverse ecological consequences to non-target species. In this study, the leaching behavior of DNT, IMD, and THM was investigated in soils collected from an active AgriLife Research Extension Center (AREC) vineyard. A series of column experiments were conducted to evaluate the leaching potential of insecticides under two experimental scenarios: a) individual pulse mode, and b) mixed pulse mode. In both scenarios, the breakthrough pattern of the insecticides in the mostly acidic to neutral vineyard soil clearly demonstrates medium to high leachability. Of the three insecticides studied for leaching, DNT has exhibited high leaching potential and exited the column with fewer pore volumes, whereas IMD was retained for longer, indicating lower leachability. Relative differences in leaching behavior of neonicotinoids could be attributed to their solubility with the leaching pattern IMD<THM<DNT showing strong correlation with increasing aqueous solubility 610mg/L<4100mg/L<39,830mg/L. Triplicate column study experiments were conducted to evaluate the consistency of the breakthrough pattern of these insecticides. The repeatability of the breakthrough curves shows that both DNT and IMD are reproducible between runs, whereas, THM shows some inconsistency. Leaching behavior of neonicotinoid insecticides based on the leachability indices such as groundwater ubiquity score, relative leaching potential, and partitioning between different environmental matrices through a fugacity-based equilibrium criterion model clearly indicates that DNT may pose a greater threat to aquatic resources compared to IMD and THM.


Journal of Eukaryotic Microbiology | 2004

Comparative effectiveness of light-microscopic techniques and PCR in detecting Thelohania solenopsae (Microsporidia) infections in red imported fire ants (Solenopsis invicta).

Maynard L. Milks; Yuliya Y. Sokolova; Irina A. Isakova; James R. Fuxa; Forrest Mitchell; Karen F. Snowden; S. Bradleigh Vinson

Abstract The main goal of this study was to compare the effectiveness of three staining techniques (calcofluor white M2R, Giemsa and modified trichrome), and the polymerase chain reaction (PCR) in detecting the microsporidium Thelohania solenopsae in red imported fire ants (Solenopsis invicta). The effect of the number of ants in a sample on the sensitivity of the staining techniques and the PCR, and the effect of three DNA extraction protocols on the sensitivity of PCR were also examined. In the first protocol, the ants were macerated and the crude homogenate was used immediately in the PCR. In the second protocol, the homogenate was placed on a special membrane (FTA card) that traps DNA, which is subsequently used in the PCR. In the third protocol, the DNA was purified from the homogenate by traditional phenol-chloroform extraction. Except for PCR using FTA cards, the sensitivity (number of samples positive for T. solenopsae) of all detection techniques increased with the number of ants in the sample. Overall, Giemsa was the least sensitive of all detection techniques. Calcofluor was more sensitive than modified trichrome with ants from one site and was equally as sensitive as PCR with crude DNA or a FTA card with ants from both sites. Trichrome staining was equally as sensitive as PCR with a FTA card at both sites, but it was less sensitive than PCR with crude DNA at one site. PCR on FTA cards was less sensitive than PCR with crude DNA for ants from one site but not the other. There was no difference whether crude or phenol-chloroform purified DNA was used as template. In summary, the results of this study show that PCR based on a crude DNA solution is equal to or more sensitive in detecting T. solenopsae than the other detection techniques investigated, and that it can be used as a reliable diagnostic tool for screening field samples of S. invicta for T. solenopsae. Nevertheless, ant smear stained with calcofluor or modified trichrome should be used to buttress findings from PCR.


Journal of Invertebrate Pathology | 1985

Pathology and bioassays of the lesser cornstalk borer (Elasmopalpus lignosellus) entomopoxvirus

Forrest Mitchell; J. W. Smith

Abstract The pathology and virulence of a naturally occurring entomopoxvirus of the lesser cornstalk borer (Elasmopalpus lignosellus) were studied in the laboratory. Diseased larvae appeared red and white, as opposed to the normal blue-green and brown color of healthy larvae. Chronic disease protracted the larval life span up to 40 days beyond normal. Infection appeared to be restricted to the hemocytes and the fat body cells. The LC50 for 1st instars was 9 spheroids; for 3rd and 4th instars 93 spheroids; and for 5th and 6th instars, ca. 700 spheroids.


Environmental Toxicology and Chemistry | 2016

Modeling photodegradation kinetics of three systemic neonicotinoids – dinotefuran, imidacloprid and thiamethoxam in aqueous and soil environment

Sudarshan Kurwadkar; Amanda Evans; Dustan Dewinne; Peter White; Forrest Mitchell

Environmental presence and retention of commonly used neonicotinoid insecticides such as dinotefuran (DNT), imidacloprid (IMD), and thiamethoxam (THM) are a cause for concern and prevention because of their potential toxicity to nontarget species. In the present study the kinetics of the photodegradation of these insecticides were investigated in water and soil compartments under natural light conditions. The results suggest that these insecticides are fairly unstable in both aqueous and soil environments when exposed to natural sunlight. All 3 insecticides exhibit strong first-order degradation rate kinetics in the aqueous phase, with rate constants kDNT , kIMD , and kTHM of 0.20 h(-1) , 0.30 h(-1) , and 0.18 h(-1) , respectively. However, in the soil phase, the modeled photodegradation kinetics appear to be biphasic, with optimal rate constants k1DNT and k2DNT of 0.0198 h(-1) and 0.0022 h(-1) and k1THM and k2THM of 0.0053 h(-1) and 0.0014 h(-1) , respectively. Differentially, in the soil phase, imidacloprid appears to follow the first-order rate kinetics with a kIMD of 0.0013 h(-1) . These results indicate that all 3 neonicotinoids are photodegradable, with higher degradation rates in aqueous environments relative to soil environments. In addition, soil-encapsulated imidacloprid appears to degrade slowly compared with dinotefuran and thiamethoxam and does not emulate the faster degradation rates observed in the aqueous phase. Environ Toxicol Chem 2016;35:1718-1726.


Journal of Invertebrate Pathology | 1983

Characterization of an entomopoxvirus of the lesser cornstalk borer (Elasmopalpus lignosellus)

Forrest Mitchell; Gale E. Smith; J. W. Smith

Abstract A biochemical and limited morphological characterization of an entomopoxvirus infecting the lesser cornstalk borer, Elasmopalpus lignosellus , was made. The oval virions measure 270 × 200 nm and the spheroids average 1.5 μm in diameter. Sodium dodecyl sulfate polyacrylamide gel electrophoresis elucidated 32 structural polypeptides with molecular weights ranging from 13,000 to 145,000. The viral genome was examined with the restriction endonuclease Eco RI. Gel electrophoresis of the digested DNA yielded 26 bands and a total molecular weight of 140.8 × 10 6 .


Plant Disease | 1999

Yellow Vine of Watermelon and Pumpkin in Tennesse

S. C. Bost; Forrest Mitchell; Ulrich Melcher; S. D. Pair; Jacqueline Fletcher; Astri Wayadande; B. D. Bruton

Yellow vine (YV) is a recently recognized decline of cucurbits expressed as plant yellowing, phloem discoloration, and death of vines as fruit approach maturity. In severely affected fields, YV incidence can range from 50 to 100% with similar yield loss. The disease has been associated with a phloem-limited, walled bacterium belonging to the gamma-3-proteobacteria (1), for which specific polymerase chain reaction (PCR) primers have been developed and used in diagnosis (2). First observed in 1988 in Oklahoma and Texas squash and pumpkin, YV was not detected in watermelon and cantaloupe until 1991. The disease has never been detected in cucumber. Efforts to date have been unsuccessful in transmitting the disease with dodder, grafting, or selected insects. Initially, the geographic range of the disease appeared to be generally confined to central and northeastern Oklahoma and north central Texas, an area known as the Cross Timbers Region. In 1997 to 1998, YV was diagnosed in commercial fields of watermelon and muskmelon from east Texas (Post Oak Savannah) and all cucurbit-growing areas of Oklahoma. In late summer 1998, symptoms similar to those of YV were observed in one watermelon (Hardeman County) and three pumpkin (Rhea and Morgan counties) fields in Tennessee where the leaves turned yellow and chlorotic and affected plants exhibited phloem discoloration. Estimated incidence of YV ranged from less than 1 to 20% of the plants in affected fields. PCR, with the YV-specific primers (2), amplified a band of the expected size (409 bp) from all watermelon and pumpkin plants exhibiting phloem discoloration. In contrast, no bands were amplified from asymptomatic (no phloem discoloration) watermelon or pumpkin. The nucleotide sequence of the DNA fragment amplified from a Tennessee watermelon and pumpkin plant was identical to that of the YV bacterium. The occurrence of YV outside of the Cross Timbers Region, and in a location as distant as Tennessee, suggests that the disease may be much more widespread than previously recognized. Diagnosis and monitoring of YV in all cucurbit-growing areas is critical for determining the geographic distribution and losses caused by this emerging disease. References: (1) F. J. Avila et al. Phytopathology 88:428, 1998. (2) U. Melcher et al. (Abstr.) Phytopathology. 89(suppl.):S95, 1999.


Journal of Environmental Sciences-china | 2013

Preliminary studies on occurrence of monensin antibiotic in Bosque River Watershed

Sudarshan Kurwadkar; Victoria Sicking; Barry D. Lambert; Anne McFarland; Forrest Mitchell

Water quality impact due to excessive nutrients has been extensively studied. In recent years, however, micro-pollutants such as pharmaceuticals and hormonal products used in animal agriculture have added an additional impact to overall water quality. Pharmaceuticals used in the poultry, swine, beef, and dairy industries have been detected in various environmental matrices such as, soil, groundwater and surface water. In this study, 26 surface water samples were collected throughout the Bosque River Watershed (BRW) with samples representing a range of land use conditions and locations of major dairy operations. Samples were analyzed using commercially available Enzyme-Linked Immunosorbent Assay test. Of the 26 samples, three samples consistently tested positive for monensin antibiotic with concentration ranging from 0.30 to 3.41 microg/L. These three samples were collected from sites that received varying amount of agriculture wastes (11.7% to 31.3%) and located downstream from sites associated with moderate levels of animal agriculture. The preliminary results suggest that there is a potential for monensin occurrence in the BRW, although initial findings indicate only very low levels.


Journal of Economic Entomology | 2009

Seasonal Increase of Xylella fastidiosa in Hemiptera Collected from Central Texas Vineyards

Forrest Mitchell; Jeff A. Brady; Blake R. Bextine; Isabelle Lauzière

ABSTRACT Yellow sticky traps were placed in six vineyards in central Texas from 2003 to 2006 and in locations outside the vineyards in 2004–2006. In total, 72 collections on 55 dates were examined. Xylem fluid-feeding insects were removed and identified to species and then analyzed by polymerase chain reaction to determine the presence or absence of Xylella fastidiosa Wells et al. Of the 1318 insects removed, 13 species were found, dominated by Homalodisca vitripennis (Germar), Clastoptera xanthocepahala Germar, and Graphocephala versuta (Say). Insects testing positive for X. fastidiosa were analyzed further using fluorescence resonance energy transfer probes to determine the genotype of the bacterium, which fell into four groups: subspecies fastidiosa, multiplex, sandyi, and unknown subspecies. Vineyards known to be affected by Pierces disease had more insects that were contaminated by the bacterium than those that were not as affected. X. fastidiosa subsp. fastidiosa, the causative agent of Pierces disease, was found more commonly in insects collected from vineyards than from insects collected outside the vineyards. Conversely, the subspecies multiplex and sandyi, which are not known to cause disease in grape, were more commonly found in insects collected outside the vineyard. The percentage of individuals contaminated with the bacterium increased over the course of the growing season, and the data suggest that vector insects acquired X. fastidiosa subsp. fastidiosa from infected grapevines, a necessary precursor for vine to vine transmission to occur. Management options, including the use of systemic insecticides and plant roguing, would be effective for this type of transmission model.

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Dustan Dewinne

Tarleton State University

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James R. Fuxa

Louisiana State University Agricultural Center

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Remington Wheat

Mansfield University of Pennsylvania

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S. D. Pair

United States Department of Agriculture

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Amanda Evans

California State University

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