Browsing by Author "Randy Wells, Committee Member"

Filter results by typing the first few letters
Now showing 1 - 10 of 10
  • No Thumbnail Available
    Defining Optimal Defoliation and Harvest Timing for Various Fruiting Patterns of Cotton in North Carolina
    (2006-05-26) Collins, Guy David; Keith Edmisten, Committee Chair; David Jordan, Committee Member; Randy Wells, Committee Member
    Upland Cotton (Gossypium hirsutum L.) is a perennial plant produced as an annual crop in North Carolina. Due to high variability in net returns, and narrow profit margins, growers must focus attention not only on lint yield but also on lint quality. Implementing sound agronomic practices, such as proper defoliation timing and harvest timing, may help maximize lint yield and fiber quality. Cotton is normally defoliated when 60 percent of the total harvestable bolls are open. It is hypothesized that defoliation could be initiated before 60 OBPD (% open bolls) if fruiting is compact, and in contrast, defoliation could be delayed beyond 60 OBPD if fruiting is extended. Two experiments were conducted in 2004 and 2005 at Upper Coastal Plains Research Station near Rocky Mount, North Carolina, to observe the effects of defoliation and harvest timings on crops of various levels of maturity or fruiting habits. One study involved plant growth regulator strategies to mimic compact, normal, and extended fruiting habits, respectively. The other study included three variety maturity groups to accomplish the various fruiting habits. The targeted defoliation timings in each study were 50, 70 and 90 OBPD and the targeted harvest timings were 14 days after defoliation and 28 days after defoliation. According to lint yield data in 2005 from the study involving plant growth regulator strategies, a crop with compact fruiting could be defoliated earlier than 60 OBPD without sacrificing yields. Delaying harvest for a crop defoliated early may help maximize yield and fiber length, whereas an early harvest may be more appropriate for a crop defoliated late, especially if significant amounts of rainfall are experienced. In 2005, micronaire values decreased 4% by delaying harvest, regardless of defoliation timing. Data also suggests that NACB (nodes above cracked boll) ~ 3 corresponded to maximum yields, especially in cases where mepiquat chloride was used. Data from the study involving various cultivars suggests that cultivar differences may be largely responsible for quality variations in micronaire, fiber length, length uniformity, and fiber strength. Defoliation before 60 OBPD was proven to be acceptable in some cases, however, harvest may need to be delayed to achieve maximum yields. In contrast, optimal yields were reached when a crop defoliated beyond 60 OBPD was harvested early. These effects were largely a result of variations in the amount of rainfall occurring during the harvest period. Data also suggests that defoliation initiated at NACB ~ 3 corresponded to maximum yields and fiber quality. Data indicated that delaying defoliation may increase yields, regardless of varieties. Plant mapping data suggests that fruiting habits were different, however, all three cultivars seemed to possess an extended fruiting habit, therefore assumptions regarding fruiting compactness can not made based on a particular cultivar maturity group.
  • No Thumbnail Available
    Dietary and Genetic Effects on Cellular Copper Homeostasis in Bovine and Porcine Tissues.
    (2010-12-07) Fry, Robert Scott; Melissa Ashwell, Committee Chair; Jerry Spears, Committee Chair; Jerry Spears, Committee Chair; ENGLE, TERRY E. (E), Committee Member; Melissa Ashwell, Committee Member; Paul Siciliano, Committee Member; Sung Kim, Committee Member; Randy Wells, Committee Member
  • No Thumbnail Available
    Distribution, Biology, and Management of Glyphosate-resistant Palmer amaranth in North Carolina
    (2009-04-23) Whitaker, Jared Ross; Alan York, Committee Chair; David Jordan, Committee Co-Chair; Randy Wells, Committee Member; Jim Burton, Committee Member
    The introduction of glyphosate-resistant (GR) crops allowed for the topical applications of the herbicide glyphosate. This herbicide revolutionized weed control and crop management. Widespread adoption of this technology and extensive use of glyphosate led to intense selection pressure for evolution of GR weeds. In 2005, GR Palmer amaranth was suspected in North Carolina. A survey detected GR populations in 49 of 290 fields sampled. ALS-inhibitor resistance was also detected in 52 fields. Five fields had populations exhibiting multiple resistance to both glyphosate and ALS-inhibitors. Experiments were conducted to determine the resistance mechanism of GR Palmer amaranth. A GR biotype exhibited a 20-fold level of resistance compared to a glyphosate-susceptible (GS) biotype. Shikimate accumulated in GS but not GR plants after glyphosate application. Maximum absorption was observed by 12 hours after treatment (HAT), and was similar among biotypes except at 6 HAT, where GS plants absorbed 67% more than GR plants. Distribution of 14C was similar among biotypes in (42%), above (30%), and below (22%) the treated leaf and in roots (6%). This work did not lead to a suggestion a resistance mechanism. Field experiments were conducted to develop management strategies for GR Palmer amaranth in cotton. One evaluated residual control of Palmer amaranth by various herbicides. Of herbicides typically applied PRE or pre-plant, fomesafen, flumioxazin, and pyrithiobac were most effective. Pyrithiobac and S-metolachlor were the most effective postemergence (POST) herbicides. Flumioxazin and prometryn plus trifloxysulfuron were the most effective options for postemergence-directed applications. Integration of these herbicides into glyphosate-based systems could increase Palmer amaranth control. An experiment was conducted to evaluate PRE herbicides in a season-long system. All PRE herbicides increased late-season control. Among individual herbicides, fomesafen and pyrithiobac were most effective. Combinations of fomesafen plus pyrithiobac or diuron and diuron plus pyrithiobac were the most effective PRE applications. Another experiment investigated herbicide systems with residual herbicides applied pre-plant, PRE and POST. Pre-plant applications of flumioxazin and PRE applications of fomesafen increased late-season control, but applications of both were more effective than either herbicide alone. Applications of glyphosate plus pyrithiobac POST were more effective than glyphosate alone. Glyphosate plus S-metolachlor was more effective than glyphosate alone at one of two locations. These data suggest early-season control of GR Palmer amaranth is critical for successful management in cotton. Glufosinate is another herbicide effective on Palmer amaranth. However, growers were reluctant to plant glufosinate-tolerant cotton cultivars. Widestrike cotton is GR and also contained a glufosinate tolerance gene used as a selectable marker, however glufosinate tolerance in production situations had not been investigated. Experiments were conducted to evaluate Widestrike cotton tolerance to glufosinate and yield was reduced by glufosinate in only one of 11 trials by 4%, suggesting acceptable tolerance. Another experiment evaluated weed control with glufosinate and glyphosate in Widestrike cotton. Control of GR Palmer amaranth by glufosinate-based systems was higher than glyphosate-based systems, which demonstrated that glufosinate-based systems could be used to control GR Palmer amaranth in Widestrike cotton. In soybean, several glyphosate alternative herbicides could be used to control Palmer amaranth. An experiment was conducted to evaluate control of GS and GR Palmer amaranth from a glyphosate-only system compared to several alternative systems. Glyphosate alone applied once POST was very effective on GS Palmer amaranth and alternative systems with two PREs followed by fomesafen POST provided similar control from glyphosate. In fields with GR Palmer amaranth, greater than 80% late-season control was obtained only with systems of two PREs followed by fomesafen POST.
  • No Thumbnail Available
    Electron microscopy complements genetic manipulation for understanding xylem development
    (2007-10-03) Avci, Utku; Ralph E. Dewey, Committee Member; Candace H. Haigler, Committee Chair; Richard L. Blanton, Committee Member; Randy Wells, Committee Member
  • No Thumbnail Available
    Evaluation of Nitrogen Sources and Rates on Yield and Quality of Modern Flue-Cured Tobacco Cultivars
    (2009-03-24) Parker, Robert Gary; Michael Wagger, Committee Member; Randy Wells, Committee Member; W. David Smith, Committee Co-Chair; Loren Fisher, Committee Co-Chair
    Nitrogen has a more pronounced effect on the growth and quality of tobacco than any other essential element even though it is not taken up in the highest quantity. Soil nitrogen regime affects plant development more than any other nutrient from seedling stage through the time of final harvest. The role of nitrogen in the development and quality of tobacco is of major importance with respect to time of absorption, form of nitrogen absorbed, rate of application, concentration in the leaf and numerous other aspects. Soil nitrogen must be sufficient during early and mid-season growth stages to ensure vigorous, but not excessive growth, and it should be nearly depleted by flowering for the plant to mature and ripen properly insuring a quality leaf. In general, as total N in the plant increases, above the amount required for maximum growth, quality of flue-cured tobacco tends to decrease. Field studies were conducted at two locations in both 2006 and in 2007 to evaluate response to nitrogen rates. Cultivars NC 71 and K 346 were selected for this study based on differences in the North Carolina Official Variety Test, with NC 71 averaging greater than 450 kg/ha more yield than K 346. Also, it has been observed that K 346 has a lower quality index than NC 71 when both varieties are produced using similar rates of nitrogen. Calcium nitrate was used as the total source of nitrogen and rates used were 45, 56, 67, 78, and 90 kg of nitrogen per hectare. Nitrogen was split applied with one half of the total applied within the first week after transplanting and the balance applied approximately 14 days later. All other production practices followed standard practices for the individual research station. There were significant main effects for variety. NC 71 averaged 3175 kg/ha while K 346 averaged 2798. There were no differences between varieties for grade index or dollars per kilogram. Dollars per hectare followed the same trend as yield with NC 71 grossing $1,247 dollars more per hectare than K 346. The main effect for nitrogen rate was also significant. Yield and dollars per hectare increased as nitrogen rate increased up to 78 kg of nitrogen per hectare. Total alkaloids increased as nitrogen increased and total reducing sugars decreased. Although yield between the cultivars was different the trends were the same with response to nitrogen. As the nitrogen rate increased, yield for both cultivars increased with no negative affect on quality. Therefore, K 346 requires the same rate of nitrogen to achieve maximum yield as NC 71 even though there was a significant difference in yield between the two cultivars. Studies were conducted at one location in 2006 and two locations in 2007 in order to determine if fertilization with urea or urea plus Agrotain (urease inhibitor) would produce flue-cured tobacco similar to that obtained from a nitrogen regime of all nitrate nitrogen. Treatments consisted of three sources of nitrogen: calcium nitrate, urea, and urea plus Agrotain and applied at rates to provide 56 and 78 kg of nitrogen per hectare. Nitrogen source did not affect yield, grade index, dollars per kilogram or total reducing sugars. However, nitrogen source did affect total value and total alkaloids. Increasing the nitrogen rate from 56 to 78 kg/ha increased dollars per hectare by $417 and increased total alkaloids from 3.46 to 3.67 percent. Calcium nitrate produced a higher return per hectare than did urea or urea plus Agrotain. Rainfall was normal for 2006 but was lower than normal for 2007, which could have slowed the rate of nitrification. From these experiments we conclude that urea or urea plus Agrotain will not produce flue-cured tobacco of equal value or similar alkaloid levels as an all nitrate regime under the environmental conditions. Field studies were conducted at two locations in 2004, 2005, and 2006 to evaluate sources and rates of nitrogen for the production of flue-cured tobacco. Calcium nitrate, ammonium nitrate, and urea ammonium nitrate (UAN) were evaluated. Sources were chosen based on previous research that provided inconsistent results when using ammonium nitrate and UAN for flue-cured production. The rates of nitrogen evaluated were 0, 22, 45, 67, and 90 kg N/ha in all years with 112 and 134 kg N/ha rates added in 2005 and 2006. All treatments received 134 kg of potassium per hectare within seven days of transplanting. Nitrogen application was applied twice with one-half of the total applied within the first week after transplanting and the balance applied approximately 14 days later. All other production practices followed standard practices for the individual research stations. Nitrogen source did not affect yield, grade index, value, total alkaloids, total reducing sugars, or leaf color. Yield increased at all locations as nitrogen rate increased up to 67 kg/ha. Yield decreased at nitrogen rate above 90 kg/ha. Dollars per hectare followed the same trends as yield since grade index was not affected by nitrogen rate. Total alkaloids increased as nitrogen rate increased up to 112 kg N/ha. Inversely, total reducing sugars decreased as nitrogen rate increased. Leaf color in the field increased as nitrogen rate increased. Soil nitrate levels increased at the highest level of nitrogen tested at both topping and final harvest sampling times. Nitrate levels at two intervals for treatments receiving 134 kg N/ha were almost double that of any other treatment tested. Ammonium levels were higher, at topping, in the top 15-cm soil samples when UAN was applied. At final harvest, soil nitrate levels were higher, in the upper 30-cm, for treatments receiving calcium nitrate.
  • No Thumbnail Available
    Fertilization Strategies of Cotton in North Carolina
    (2009-06-01) Hunt, Andrew David; David Jordan, Committee Member; Randy Wells, Committee Member; Keith Edmisten, Committee Chair
    Upland cotton (Gossypium hirsutum L.) can be a difficult crop to manage due to the intermediate growth habits, tropical origins, and perennial nature. Because cotton is produced as an annual in North Carolina, it is highly important to promote maximum early season growth, stimulate early flowering, and at the same time prevent excessive vegetative growth, all which are important to harvest quality cotton. The use of several management practices may be applied to promote earliness, and achieve high yields. While environmental conditions can generally not be controlled, they can be altered thorough tillage methods, plant growth regulator use, and desirable fertilization programs, to manipulate cotton vegetative and reproductive growth to promote high yields. Three studies were conducted to observe fertilization strategies for cotton production in North Carolina. One study was conducted in North Carolina and Virginia during 2005 and 2006 to determine effects of increased N fertilization rates and increased plant growth regulator rates on a modern cultivar. The second study were conducted in North Carolina in 2006 and 2007 to observe the effects of effects of starter fertilizer in conventional, strip†till (ST) and no†till (NT) systems on growth, quality and yield of cotton. The third study was conducted in North Carolina in 2006 and 2007 to determine optimal N placement methods in strip†till (ST) and no†till (NT) systems based on growth, fiber quality, and yield of cotton. Data from the first study showed that N rate affected yield in Virginia in both years and in North Carolina during 2006. However, in 2005 N did not affect yield. In North Carolina 2006 the response to N was quadratic, while in the Virginia locations the response to N was linear, however, further increase in N above 112 kg N ha†1 was not significant. Overall the use of a plant growth regulator did not alter the optimum N rate. For the second starter fertilizer did not have an effect on yield in either year. Starter fertilizers did have an effect on early season vigor and plant heights in 2006 with the 11†37†0 fertilizers having greater vigor and heights. In 2006 and 2007 11†37†0 fertilizers had the highest dry weights. Data from both years suggest that tillage has an influence on early season growth such as vigor, stand counts, and early season heights. Data from 2007 indicates that more bolls may be produced in NT systems, however, the number of bolls did not correspond to an increase in lint yield. Little agronomic advantage was found in starter fertilizer, with no positive or negative effect on yield when compared to an untreated control. There is no conclusive evidence from the data that starter fertilizer responses are more likely for any tillage system. For the third study data from 2006 found that under reduced tillage systems broadcasting N was sufficient, while injecting N did not improve final yield. Data from 2007 indicates that the placement of fertilizer N at first square had no significant effect on final yield. Due to the lack of sufficient tillage by N method interactions, it is likely that all N application methods would perform similarly in both tillage systems. Based on these data an optimal N placement strategy could not be determined based on the data, due to the inconclusive results regarding application method effects on growth and yield.
  • No Thumbnail Available
    Influence of Environmental and Physiological Factors on Glufosinate and Glyphosate Weed Management.
    (2007-12-19) Everman, Wesley J.; David L. Jordan, Committee Member; Randy Wells, Committee Member; James D. Burton, Committee Member; Alan C. York, Committee Chair
    Field studies were conducted near Clayton, Lewiston, and Rocky Mount, NC in 2005 to evaluate weed control and cotton response to PRE treatments of pendimethalin alone or in a tank mixture with fomesafen, POST treatments of glufosinate applied alone or in a tank mixture with S-metolachlor, and LAYBY treatments of glufosinate in a tank mixture with flumioxazin or prometryn. Field studies were conducted near Clayton, Goldsboro, Kinston, and Rocky Mount, NC in 2003 to evaluate weed control and cotton response to POST treatments of glufosinate applied alone or in tank mixtures with S-metolachlor, pyrithiobac, or trifloxysulfuron. Field studies were conducted near Rocky Mount, NC in 2004, Clayton, NC, Lewiston-Woodville, NC, Florence, SC, St. Joseph, LA, and Suffolk, VA in 2005 to evaluate weed control and cotton response to postemergence treatments of glufosinate or glyphosate on glufosinate-resistant and glyphosate-resistant cotton, respectively, applied alone or in tank mixtures with S-metolachlor EPOST. Greenhouse studies were conducted to evaluate phytotoxicity and corresponding physiological response to simulated rainfall following POST treatments of various formulations of glufosinate or glyphosate on goosegrass, Palmer amaranth, and pitted morningglory. Ammonia levels and shikimic acid levels were used as diagnostic markers for glufosinate and glyphosate, respectively. A rain-free period of 4 hours is needed to adequately control goosegrass and Palmer amaranth, while up to 24 hours is needed to control pitted morningglory with glyphosate. A rain-free period of 1 hour is needed to provide maximum control of goosegrass and pitted morningglory with glufosinate; however a rain-free period of at least 24 hours is needed to achieve maximum control of Palmer amaranth. Greenhouse studies were conducted to evaluate absorption, translocation, and metabolism of 14C-glufosinate in glufosinate-resistant corn, glufosinate-resistant cotton, non-transgenic cotton, goosegrass, large crabgrass, Palmer amaranth, pitted morningglory, and sicklepod. Absorption of 14C-glufosinate varied by species. Significant levels of translocation were observed in glufosinate-resistant corn and Palmer amaranth. Metabolites of 14C-glufosinate were detected in all crop and weed species.
  • No Thumbnail Available
    Modeling the Mechanical Behavior of Transgenic Aspen with Altered Lignin Content and Composition.
    (2010-06-23) Horvath, Laszlo; Ilona Peszlen, Committee Chair; Perry Peralta, Committee Chair; Melur Ramasubramanian, Committee Member; Hou-Min Chang, Committee Member; Sunkyu Park, Committee Member; Randy Wells, Committee Member
  • No Thumbnail Available
    Orchard Floor Management in Young Peach: Effects of Irrigation, Vegetation-free Width, and Certain PRE Herbicides
    (2009-08-03) Buckelew, Juliana Kirsten; Michael Burton, Committee Member; Michael Parker, Committee Member; David Monks, Committee Chair; Randy Wells, Committee Member
    A hindrance to peach culture in the southeastern U.S. is orchard floor vegetation in which weeds can compete for water and nutrients. Young orchards may take longer to come into production if infested with weeds. The common orchard floor management system in the southeastern U.S. is a 3.0 to 3.6 m wide vegetation-free strip in the tree row with an orchard cover of volunteer weedy vegetation. However, reduction of the strip width may be possible through the use of irrigation which could reduce herbicide use. Thus, the objective of our study was to determine the optimum vegetation-free strip for irrigated peach with a weedy groundcover. Research was conducted in 2006 to 2008 to determine the optimum vegetation-free strip for irrigated peach with a weedy groundcover, and to evaluate PRE-emergence directed control of weeds that infest peach in North Carolina. The first experiment included two factors, vegetation-free widths (VFW) of 0, 0.6, 1.2, 2.4, 3, and 3.6 m and irrigation (either irrigated or nonirrigated). At Jackson Springs, NC, the irrigated vegetation-free width (VFW) which would produce the same yield season total (kg/ha) as the grower standard (3.6 nonirrigated) is 1.16 m, based on results from regression. (For maximum season total, the VFW needed to be 3.6 m.) The irrigated VFWs which would produce the same tree cross-sectional area as the grower standard was 1.5, 1.3 and 0.8 m for trees aged one, two, and three years old, respectively. At Clayton, NC, trunk cross-sectional area in 2007 and 2008 and harvest season totals were not different by irrigation, but did increase linearly with VFW. At both locations, water and nitrogen were probably the limiting factors. Similar across locations, leaf nitrogen concentrations were lower but not deficient in the irrigated trees than the nonirrigated trees, presumably due to leaching of NO3 by irrigation. Foliar N, SPAD measurements, soil moisture, and growth responses were positively related to VFW at Jackson Springs therefore growth responses there were probably due to water and N competition with vegetation. In contrast, foliar N concentration was not different by VFW at Clayton. However, growth responses were positively related to VFW. SPAD measurements increased with VFW so vegetation had some effect on nitrogen. For the first two years of the study, VFW did have an effect on soil moisture at 30 cm depth. Data suggest that a 1.5 m VFW combined with proper irrigation and fertilization will produce tree growth and yield in volunteer weedy vegetation similar to the current grower standard. Field experiments were conducted in 2006 and 2007 to determine newly planted peach tolerance to sulfentrazone herbicide applied PRE at various rates and to determine the effect of sequential sulfentrazone when tank mixed with other PRE herbicides on peach tolerance and weed suppression. Henbit, common lambsquarters, large crabgrass, and yellow foxtail were present at the study sites. For tolerance studies, treatments were 0.21, 0.28, 0.35, and 0.42 kg / ha sulfentrazone. For the systems study, treatments were 0.21 kg / ha sulfentrazone, 0.28 kg / ha sulfentrazone, 0.21 kg / ha sulfentrazone plus 1.34 kg / ha norflurazon, 0.28 kg / ha sulfentrazone plus 1.34 kg / ha norflurazon, 0.21 kg / ha sulfentrazone plus 1.12 kg / ha oryzalin, 0.28 kg / ha sulfentrazone plus 1.12 oryzalin, 0.89 kg / ha terbacil, 0.89 kg / ha terbacil plus 1.12 kg / ha rimsulfuron, and 0.28 kg / ha flumioxazin. Sulfentrazone PRE did not injure newly planted peach trees. Sulfentrazone alone controlled several broadleaf weeds however it did not adequately control large crabgrass and yellow foxtail. Control of these grasses increased with the addition of norflurazon or oryzalin. Norflurazon and rimsulfuron were safe for peach trees when applied as a tank mix partner in this study, therefore deserve further investigation for weed control in newly planted peach. Sulfentrazone was safe to newly planted peach and likely would be useful to growers developing weed management programs for peach. Field experiments were also conducted in 2006 and 2007 to determine tolerance to halosulfuron, mesotrione, and rimsulfuron applied at various rates on newly planted peach. The halosulfuron study included treatments 0, 26.3, 52.5, 79, and 105 g / ha. The mesotrione study included treatments 0, 105.7, 140.3, 211.4, and 280.1 g / ha. The rimsulfuron study included treatments 0, 70, 140, 210, and 280 g / ha. Halosulfuron, mesotrione and rimsulfuron did not reduce trunk cross-sectional area (TCSA) or winter pruning weight relative to the nontreated check. In 2006, no injury from halosulfuron occurred at 1 WAT, but at 3 WAT injury was 39 to 50 % on the highest rates of the study at 79 and 105 g / ha, respectively. Partial recovery of peach was seen at 5 WAT, as shown by 12 and 24 % injury on the highest rates (79 and 105 g / ha) of the study, respectively. No visual injury symptoms occurred in 2007 for any study. Mesotrione and rimsulfuron were safe to newly planted peach and likely would be useful to growers developing weed management programs for peach. Halosulfuron at the higher rates caused visual injury but did not reduce TCSA or winter pruning weight. Therefore, further testing is needed to define conditions that may contribute to injury from halosulfuron.
  • No Thumbnail Available
    Reducing Costs and Optimizing the Timing of Agronomic Inputs for Cotton (Gossypium hirsutum L.) in North Carolina.
    (2009-10-01) Collins, Guy David; Alan York, Committee Member; Jack Bacheler, Committee Member; Keith Edmisten, Committee Chair; Randy Wells, Committee Member
    Cotton (Gossypium hirsutum L.) grown in North Carolina requires intensive management for achieving optimal yields in an early-season environment. Recent increases in production costs require cotton producers to adopt practices that allow yield potential to be reached, while reducing input costs or optimizing the timing of agronomic inputs. Six experiments were conducted in North Carolina from 2006 to 2008 to investigate various production practices that could potentially reduce production costs and to define optimal timings of agronomic inputs. The first experiment investigated precision application of in-furrow insecticides for cotton planted in a hill-dropped configuration. The second experiment investigated application rates and timings of mepiquat chloride (MC) for cotton grown in conditions that promote excessive vegetative growth. The third experiment investigated the effects of MC applied at various rates and timings on the correlation (regression) between two techniques for measuring light interception and canopy coverage: the light quantum sensor method and the overhead digital imagery method. The fourth experiment investigated the effects of MC applied at physiological cutout, in terms of defoliation, regrowth, maturity, and yield. The fifth experiment investigated the effects of preconditioning defoliation treatments for tall cotton portraying dense canopies which improve standard defoliation practices and the timeliness of harvest. The sixth experiment investigated the effects of ethephon rate in defoliant mixtures on harvest date, with regard to defoliation timing and prior MC treatment.