Introduction

Harvesting peanut (Arachis hypogea L.) when the highest percentage of pods are at optimal maturity is critical for farmers to attain the highest profit from their crop. For the past two decades, most growers have been using the hull scrape method in conjunction with methods akin to the maturity profile board, employing the correlation between pod maturity and mesocarp color to project optimal harvest time (Colvin et al., 2014; Williams and Drexler, 1981). Predicting maturity in peanut can be difficult as peanut grows in an indeterminate manner, and how quickly a field matures is highly influenced by the amount of rainfall and the temperature during each growing season (Jordan et al., 1998). Inverting a crop too early or too late leads to negative impacts on yield, market grade and profitability (Anco et al., 2024; Jordan et al., 1998, 2016; Mozingo et al., 1991; Wright and Porter, 1991). Digging a crop prior to optimum maturity additionally leads to more immature peanuts entering storage facilities which may increase the risk of toxic mold (Aspergillus flavus) production (Sorenson et al., 2015). Immature peanuts have also more commonly been reported to develop fruity off-flavors and less roasted peanut flavor after being cured (Sanders et al., 1989; Sanders et al., 1990). Conversely, when a field is dug too late, yield loss can increase due to mechanical or biological damage on overmature plants with weakened or diseased pegs (Chapin and Thomas, 2005; Sorenson et al., 2015).

Many recently released cultivars offer growers yield benefits and improved disease resistance packages when compared to their predecessors (Anco and Hiers, 2022). However, many of these newer cultivars have also taken between 10 to 15 days longer to reach pod maturity levels comparable to those traditionally considered optimal (i.e., >75% mature pods, Boote 1982) to serve as a target for inversion (Anco et al., 2024). This has in recent years resulted in newer cultivars Georgia-16HO (Branch, 2017), FloRun 331(Tillman, 2021), and TUFRunner 297 (Tillman, 2018) being given 150 or more days after planting (DAP) to approach pod maturity levels that older and earlier maturing cultivars Georgia-06G (Branch, 2007) and Georgia-09B (Branch, 2010) generally obtain in 140 or 135 DAP, respectively (Anco et al., 2024).

There are several yield-limiting fungal diseases that can potentially cause significant economic losses in peanut production. In South Carolina, late leaf spot, caused by Nothopassalora personata ((Berk and M.A. Curtis) S.A. Kahn and M. Kamal), is the most consistent cause of economic losses among fungal pathogens (Anco, 2023). In order to manage late leaf spot, it is recommended that commercial growers initiate a fungicide application program beginning at 30 DAP and consisting of five to seven applications in 14-day intervals (Anco, 2023). When a growing season is extended into October and November to allow a maturing crop to reach optimal maturity, cooler temperatures and shorter days become more favorable for late leaf spot (Alderman and Nutter, 1994) and other late-season diseases (Davidson et al., 1991), causing many producers to apply one more fungicide spray to extend protective coverage. If this late season fungicide spray could be avoided, it could increase revenue by ~$15 per hectare, not including equipment or labor. Another added risk of late season harvest is the increased risk of slower drying conditions and frost damage after inversion (Jordan et al., 2019), both of which can lead to the crop being graded as segregation II. Segregation II peanuts have no visible Aspergillus flavus mold but contain over 3.49% damaged kernels, including physical, concealed (i.e. mold or decaying kernels) or freeze damage (American Peanut Shellers Association, 2020). If yield potential could be maintained while maturity was simultaneously hastened, this would save time and revenue for growers.

Peanuts are commonly planted in either single row (91 to 102 cm apart) or twin row arrangement (18 cm between two rows of peanuts, on 91 to 102 cm centers), often on an elevated bed (Lanier et al., 2004; Sorenson et al., 2007; Wehtje et al., 1984). Planting in twin rows versus single rows increases the plant population from 19 seeds per meter in single rows to 23 seeds per meter spread between two rows, which effectively decreases the intra-row competition while also increasing plant populations (Sorenson et al., 2004). Previous research has consistently reported a significant yield advantage when peanuts are planted in a twin row arrangement (Lanier et al., 2004; Nuti et al., 2008; Tillman et al., 2006; Tubbs et al., 2011; Wehtje et al., 1984). The amount of thrips (e.g., Frankliniella fusca [Pergande] and F. occidentalis [Hinds]) injury and tomato spotted wilt (TSW) infection that typically follows thrips infestations has repeatedly been reported to be reduced in twins compared to single rows (Baldwin et al., 2001; Culbreath et al., 2008; Tubbs et al., 2011). Several studies have also reported higher market grades (total sound mature kernels; TSMK) when peanut is planted in twin rows (Lanier et al., 2004; Sorenson et al., 2004, 2007).

Twin row configuration reduces the time normally required for peanut to lap the row. This earlier shading of the ground aids in reducing soil geocarposphere temperatures. Davidson et al., (1991) reported a reduction in premium priced kernels when severe drought and high geocarposphere temperatures led to a delay in fruit initiation; additionally, high geocarposphere temperatures were typically associated with a smaller canopy, reduced yield, and poorer quality. A delay in fruit initiation can lead to an increased limb crop (addition of small pods away from the taproot) instead of a taproot crop (addition of large pods near the taproot) (Davidson et al., 1991). Being set first, a taproot crop will mature earlier than a limb crop. Encouraging more of a taproot focused crop and less of a limb crop potentially may hasten maturity and produce a more uniform maturity, due to optimal maturity applying more to one crop rather than the balance between two crops (i.e., taproot versus limb crop) that have begun to be set at different points in the season. Twin row planting has anecdotally been associated with more of a taproot crop compared to single rows. However, the distribution of pods produced in association with a taproot versus limb crop and the maturity development of produced pods have not been quantitatively reported for twin versus single row planting configurations, and formal quantitative definitions delineating taproot versus limb crops are lacking.

Peanut has been reported to produce more vegetative growth than necessary to reach maximum pod yield, where nutrients and photosynthate are directed to vegetative growth instead of developing pods (Mitchem et al., 1996). Excessive vine growth leads to decreased disease resistance (Phipps, 1995), and a dense canopy will inhibit pesticides from contacting lower leaves (Mitchem et al., 1996). A larger canopy has been reported to decrease inversion and harvest efficiency (Beam et al., 2002). Classic runner type peanuts, such as the widely used cultivar Georgia-06G, grow a smaller and more compact canopy. Virginia market types like Bailey II characteristically exhibit a larger and more robust canopy which intertwines among adjacent rows and can make digging without GPS assistance more difficult due to reduced visual distinction of rows (Beam et al., 2002). Plant growth regulators have been studied and employed for decades to manage excessive vine growth in peanut, with most studies having focused on Virginia-types due to their larger canopies.

Prohexadione calcium (a calcium salt of 3,5-dioxo-4 propionylcyclohexanecarboxylic acid) is a plant growth regulator used in the production of peanut, apple (Malus x domestica Borkh.), pear (Pyrus communis L.), cherry (Prunus avium L.), grain sorghum [Sorghum bicolor (L.) Moench], oilseed rape (Brassica napus L.), rice (Oryza sativa L.), tomato (Solanum lycopersicum L.), and wheat (Triticum aestivum L.) to decelerate the rate of vegetative growth (BASF, 2012; Byers and Yoder, 1999; Grossman et al., 1994; Lee et al., 1998; Mitchem et al. 1996; Nakayama et al., 1992; Yamaji et al., 1991). Prohexadione calcium inhibits the biosynthesis of plant hormone gibberellin, which causes a reduction in shoot growth and decreased cell elongation (BASF, 2012; Grossman et al., 1994). Prohexadione calcium inhibits gibberellin biosynthesis by blocking kaurene oxidase and increases the level of abscisic acid and cytokines in certain species (Grossman et al., 1994).

In the last decade, breeding programs have released runner market type peanut cultivars with larger canopies, producing a need for managing excessive vine growth. More recent studies have reported yield improvement and canopy size reduction on runner type cultivars following the application of prohexadione calcium at a 0.75× rate (Monfort et al., 2021; Studstill et al., 2020). Early studies of prohexadione calcium reported a significant increase in the earliness of Virginia type cultivars. Culpepper et al. (1997) reported a 9% increase, while Mitchem et al. (1996) reported a 19% increase in the percent of orange, brown or black pods near harvest when treated with prohexadione calcium. Nevertheless, cultivars that were used in those studies (AT VC 1, NC 9, NC 10C, NC-V 11, and VA-C 92R) are no longer commercially grown. Furthermore, pods collected for maturity determination in both of these studies were obtained following mechanical inversion by the digger-shaker-inverter. Consequently, this could have confounded measurements of the magnitude of response of maturity development as a result of prohexadione calcium application since it introduces the potential for non-constant pod loss as a function of varying canopy size and corresponding resistance to flow as dug peanut pass through the digger and interface with the star wheels.

Information regarding the effect of prohexadione calcium on the maturity of newer cultivars is lacking. Additionally, most research that has involved prohexadione calcium has either evaluated single row planting or Virginia market type peanut. Therefore, research was conducted to evaluate the combined and independent effects of prohexadione calcium and row pattern on maturity development and pod distribution of peanut in South Carolina, specifically with respect to newer runner cultivars.

Materials and Methods

Field experiments were conducted during the 2021 and 2022 growing seasons in different fields at Clemson University’s Edisto Research and Education Center (EREC; 33.3648N,

81.3298W) in Blackville, SC on a Barnwell loamy sand (fine-loamy, kaolinitic, thermic Typic Kanhapludults; irrigated) and at Pee Dee Research and Education Center (PDREC; 34.2898N, 79.7388W) in Florence, SC on a Norfolk loamy sand (fine-loamy, kaolinitic, thermic Typic Kandiudults; dryland). Plot dimensions consisted of four rows wide (3.9 m) by 30.5 m in length, which were separated into two yield rows and two traffic rows. Yield rows were used for data collection while traffic rows were used to drive over to apply prohexadione calcium and maintenance agrochemicals. A split plot experimental design was utilized, with the interaction of row pattern and growth regulator application as the main plot and cultivar as the sub plot. Treatments were replicated five (EREC: 2021 and 2022; PDREC: 2021) or four times (PDREC: 2022). Single rows were spaced 96-cm apart and planted at a rate of 19 seeds per m, while twin rows were spaced 18-cm apart on 96-cm centers and planted at a rate of 23 seeds per m based on planter settings.

Three runner-type cultivars and one Virginia type cultivar were selected based on frequency of use by SC farmers and desired optimal maturity requirements. Cultivars were then paired into separate experiments based on maturity – earlier maturing cultivars (E, i.e., ~138 to 140 DAP) and later maturing cultivars (L, i.e., ~145 to 150 DAP) (Anco et al. 2021). In 2021, planted cultivars were Bailey II (E), Georgia-06G (E), FloRun 331 (L) and Georgia-16HO (L). The later maturing experiment was planted at EREC on 10 May and earlier maturing experiment was planted 11 May. All cultivars were planted at PDREC on 1 June. In 2022, cultivars included Emery (E), Georgia-06G (E), FloRun 331 (L) and Georgia-16HO (L); EREC was planted on 5 May, and at PDREC twin rows were planted on 18 May and single rows were planted the following day, 19 May.

In 2021, TSW incidence was evaluated at 69 (E) and 70 (L) DAP (19 July) at EREC and at 65 DAP (5 August) at PDREC. In 2022, TSW incidence was evaluated at 74 DAP (18 July) at EREC and at 61 (single rows) and 62 (twin rows) DAP (19 July) at PDREC. Incidence of TSW (i.e., percent of symptomatic length from two rows) was rated using methodology previously detailed in Haynes et al. (2019). Late leaf spot (LLS) was measured as percentage incidence prior to inversion following its development in the field where applicable. If any defoliation from LLS was seen, it was recorded as a percentage as well. Early leaf spot was not present.

Canopy temperature at ground level was measured in 15 minute intervals using RC-5 USB temperature loggers (i.e., three replications per experiment). Loggers were installed at approximately 35 to 40 DAP, once the crop was large enough to begin shading the ground. Loggers were individually placed into a plastic bag to protect them from the elements, then installed approximately 25 cm off-center from the planted row. Daytime temperatures were approximately defined as those occurring from 6:00 am to 7:00 pm. When 50% of the lateral vines from adjacent rows began touching (i.e., 50% row lap), prohexadione calcium was applied at 0.75× the label rate, with a second application applied 14 days later, using a tractor mounted boom sprayer with two DG 8002 nozzles/row delivering 140 L/ha at 345 kPa. Per the prohexadione calcium label, crop oil concentrate and ammonium sulfate were applied with the growth regulator at respective rates of 2.33 L/ha and 1.17 L/ha.

Following prohexadione calcium application, row visibility was visually assessed using a 1 to 10 scale, with 1 being a flat canopy and 10 being a triangular canopy (Mitchem et al., 1996). Main stem height in cm from four plants per plot were measured in addition to row visibility. In 2021, main stem heights and row visibility was assessed at 139 (E) and 140 (L) DAP (27 September) at EREC and 139 DAP (18 October) at PDREC. In 2022, row visibility was assessed at 134 DAP (16 September) at EREC and 128 (twin rows) and 127 (single rows) DAP (23 September) at PDREC. Plots were dug based on pod mesocarp color (William and Drexler, 1981) at a time reasonable for each experiment. Peanut production management practices followed Clemson University Extension recommendations (Anco et al., 2021).

In 2021, plots were inverted on 20 October (PDREC), 28 September (EREC E group), and 5 October (EREC L group); then combined on 18 November (PDREC), 11 October (EREC E group) and 18 October (EREC L group). In 2022, plots were inverted on 6 October (PDREC), 23 September (EREC E group), and 3 October (EREC L group); then combined on 19 October (PDREC), 28 September (EREC E group) and 17 October (EREC L group). Pod yield (kg/ha) data were collected from two rows per plot with a Hobbs 2-row combine using load cells mounted to the weight basket of the combine. A 500-g subsample of peanuts was collected from plots located at EREC and graded according to USDA standards. Grade and pod yield data was then used to calculate economic value, calculated as treatment net loan value × treatment yield – treatment costs. Net loan values were calculated using the following formulae (Haynes et al., 2019; USDA FSA 2019):

Runner net loan value =

%TSMK×Loan Rate per %TSMK+%OK×Loan Rate per %OK-deductions

Virginia net loan value =

%TSMK×Loan Rate per %TSMK+%OK×Loan Rate per %OK+ %ELK×Loan Rate per %ELK-deductions

where TSMK is total sound mature kernels, OK is other kernels, and ELK is extra-large kernels. Loan rates for 2021 were $5.308 (% TSMK for runner market types), $5.414 (% TSMK for Virginia market types), $1.544 (% OK), and $0.386 (% ELK) (USDA FSA 2021). Loan rates for 2022 were $5.281 (%TSMK for runner market types), $5.387 (% TSMK for Virginia market types), $1.544 (% OK), and $0.386 (% ELK) (USDA FSA 2022). Deductions were $0.88 for each percent of sound splits over 4%. Listed loan rates and deductions correspond to pod yield in units of 1,000 kg/ha. Treatment costs were obtained from the 2022 South Carolina Agronomic Crop Production Budget ( https://blogs.clemson.edu/sccrops/files/2022/03/Production-Guide-2022-web-version.pdf). Local treatment cost for prohexadione calcium was $40.31 per hectare for both twin and single row planting pattern. Inoculant cost per hectare was $46.68 and $93.37 for single and twin row pattern, respectively. Phorate cost per hectare was $41.57 and $53.06 for single and twin rows, respectively.

Results

Early maturing experiment

Incidence of TSW was significantly greater among single rows compared to twins at EREC in both 2021 and 2022 (P = 0.0051 and P = 0.038, respectively). Conversely, no significant differences between row patterns or cultivars were seen at PDREC in either year. Tomato spotted wilt incidence of all treatments was less than 5%, with pooled results across years reported in Table 1. Row visibility was significantly greater following the application of prohexadione calcium at 0.75× (P = 0.0005), indicating prohexadione calcium made the canopy more triangular. Though single row planting pattern often had a numerical advantage in row visibility over twin rows, this was only significant in EREC in 2021 (P = 0.0085). From the pooled data, main stem heights of plots treated with prohexadione calcium were significantly shorter than those of untreated plots (32.7 vs. 35.6 cm, P < 0.0001). Main stem heights of twin rows (36.6 cm) were taller than those of single rows (31.8 cm) (P < 0.0001), and Virginia cultivars were taller than Georgia-06G (38.0 vs. 30.6 cm, P < 0.0001).

Table 1

Influence of row pattern on the percentage of spotted wilt incidence from experiments conducted in 2021 and 2022 at the Edisto Research and Education Center (EREC) and the Pee Dee Research and Education Center (PDREC).

In 2021 maturity samples were dug at 121, 133 and 140 DAP. Twin row planting pattern exhibited a significantly greater percentage of orange, brown, or black (OBB) pods when compared to corresponding single row plots (57 vs. 52%, respectively, P = 0.0393). In 2022, samples were dug at 125, 132 and 144 (Georgia-06G only) DAP. In 2022, no treatment effects significantly influenced the percentage of OBB pods. When results were pooled across years, twin rows had a significantly greater percentage of OBB pods than single rows for Georgia-06G (66 vs. 60%, respectively, P = 0.0014) but not Virginia cultivars (67 vs. 65%, respectively, P = 0.2750). Maturity during the latter two assessments (> 130 DAP) were greater than that of the first (121 to 125 DAP) (P < 0.0001, Table 2).

Table 2

Influence of row pattern and prohexadione calcium application on % orange, brown or black (OBB) pod maturity from earlier maturing cultivars from pooled experiments conducted in 2021 and 2022.

When canopy temperature was analyzed, plots treated with prohexadione calcium overall had a significantly lower average daytime temperature than untreated plots (30.0 vs. 30.3 C, respectively, P = 0.0007). Single row plots had a greater mean daytime temperature than twins by ~0.6 C (P < 0.0001). Across the pooled cultivar data, single rows with or without prohexadione calcium had warmer canopies than corresponding twin row untreated plots (~30.5 vs. 30.1 C, respectively; row pattern × growth regulator P = 0.0004), with twin rows with prohexadione calcium treatment in turn exhibiting cooler temperatures (~29.4 C). Within the Georgia-06G data (P < 0.0001), single rows with prohexadione calcium (30.9 C) were warmer than untreated single rows (30.4 C), both of which were not different from untreated twin rows (~30.6 C), all of which being warmer than treated twin rows (29.5 C). Virginia cultivar average daytime temperatures (P < 0.0001) exhibited a slightly different response, as twin rows with or without prohexadione calcium treatment (~29.6 C) had the coolest temperatures followed by single rows with prohexadione calcium treatment (30.0 C) which were in turn cooler than untreated single rows (30.4 C).

Prohexadione calcium did not significantly affect yield at either location during either year. Twin row planted plots yielded significantly greater than single row plots when data were combined across years and locations at P = 0.0319. In 2021 at PDREC, the experimental field was heavily defoliated by LLS, in which single row planted plots had a significantly greater pod yield than twin rows at P = 0.0186 (3799 vs. 3352 kg/ha). Individual year results and combined results across years and locations can be found in Table 3.

Table 3

Influence of row pattern and prohexadione calcium application on pod yield (kg/ha) from earlier maturing cultivars from experiments conducted in 2021 and 2022 at the Edisto Research and Education Center (EREC) and the Pee Dee Research and Education Center (PDREC).

Regardless of cultivar, twin row planted plots with no prohexadione calcium application had pod sets distributed significantly closer to the taproot than treated twin rows, both of which were closer distributed than single rows with prohexadione calcium treatment (< 60% pod pixels). Pod distributions of single rows without treatment were not different from single rows with treatment, were wider than that of twin rows without prohexadione calcium (< 60% pod pixels), and were 0.036 wider than treated twin rows from 50 to 60% pod pixels (Figure 1; prohexadione calcium application × pattern × % pod pixels interaction P = 0.0306).

Figure 1. Influence of row planting pattern and prohexadione calcium (PC) application (“+” = applied, “-” = not applied) on the ratio of radii corresponding to % pod pixels : radii of total pixels among pooled earlier maturing cultivars. Estimated means at the same % total pod pixels followed by different letters are significantly different according to the method of Benjamini-Hochberg at α = 0.10.

Twin row planting arrangement had a significantly greater percentage of TSMK than single row planted plots (69 vs. 67%, respectively, P = 0.0040). Row pattern was the only effect to have a significant influence on TSMK. At EREC in 2021, cultivar Emery planted in single rows with prohexadione calcium application had a significantly greater economic return than corresponding single rows with no prohexadione calcium application ($936 vs. $832 per hectare, respectively, at P = 0.0921). Similarly, cultivar Georgia-06G planted in single rows without prohexadione calcium was valued significantly higher than corresponding plots treated with prohexadione calcium ($929 vs. $832 per hectare, respectively). Additionally in 2021, twin row planted plots had a significantly greater economic value than single row plots ($1080 vs. $875 per hectare, respectively, at P < 0.0001), though this observation did not continue in 2022 when no treatment effects significantly affected economic return. Across the combined data, twin row planted plots exhibited significantly greater economic value than single rows ($1321 vs. $1124 per hectare, respectively, at P < 0.0001). Remaining treatment effects did not significantly affect economic return.

Pod OBB maturity was negatively correlated with Temp (ρ = ~ -0.54) and Tmax36p (ρ = -0.44 to -0.53) and positively correlated with main stem height (ρ = 0.65 to 0.54), TSMK (ρ = 0.21 to 0.71), and yield (ρ = 0.67 to 0.52) for both Georgia-06G and Virginia cultivars. Main stem heights were negatively correlated with Temp and Tmax36p, with this being slightly stronger for Virginia cultivars (Table 4). Pod pixel radius ratios (70% pixels) were somewhat negatively correlated with examined temperature variables (ρ = -0.21 to -0.26) for Georgia-06G but somewhat positively correlated for Virginia cultivars (ρ = ~ 0.22). Pod ratios were also negatively associated with TSMK for Georgia-06G (ρ = ~ -0.31) but not for Virginia cultivars. Virginia cultivar pod ratios were somewhat negatively correlated with pod yield (ρ = -0.25 to

Table 4

Spearman correlation coefficients of variable^a measurements for Georgia-06G (above the diagonal) and Virginia cultivars (below the diagonal).

-0.30) and slightly negatively associated with main stem heights (ρ = -0.17 to -0.19). Examined temperature variables were more strongly negatively correlated with TSMK for Virginia cultivars than for Georgia-06G (ρ = ~ -0.7 and ~ -0.3, respectively). Stem heights and pod yield were also more strongly correlated with TSMK for Virginia cultivars than for Georgia-06G (ρ = 0.59 and 0.60 compared to 0.37 and 0.25, respectively). Georgia-06G main stem heights were positively correlated with pod yield at ρ = 0.47, whereas this was not significant among Virginia cultivars. Pod yield for Georgia-06G was somewhat negatively correlated with examined temperature variables (ρ = -0.26 and -0.33).

Later maturing experiment

Incidence of TSW was significantly greater in single rows when compared to twins at EREC in 2021 and at PDREC in 2022 (P = 0.0011 and 0.0040, respectively). There were no significant differences between row patterns at PDREC in 2021 or at EREC in 2022. In 2021 at PDREC, cultivar Georgia-16HO had significantly greater TSW incidence than FloRun 331 (5.7 vs. 3.5, respectively, P = 0.0025). Conversely, in 2022 at EREC cultivar FloRun 331 had a significantly higher incidence than Georgia-16HO (3.4 vs. 2.0, respectively, at P = 0.0437).

Row visibility was significantly greater following application of prohexadione calcium at P = 0.0010. Cultivar FloRun 331 had a less visibly distinguishable canopy than Georgia-16HO (3.75 vs. 4.69; P = 0.0010). Additionally, FloRun 331 had a significantly taller average main stem height than Georgia-16HO (31.3 vs. 28.6 cm, P < 0.0001), potentially accounting for reduced row visibility. Main stem height was found to be ~3.5 cm shorter in both single and twin row plots following treatment with prohexadione calcium (P < 0.0001). Twin rows exhibited greater main stem lengths compared to single rows (32.3 vs. 27.8 cm, P < 0.0001).

When maturity development was evaluated at EREC in 2021, plots were sampled at 121, 133, and 140 DAP. The greatest percentages of OBB pods were found among samples pulled at 140 DAP (59%, P < 0.0001). Single row plots had a higher percentage of OBB pods than corresponding twin row plots at 133 DAP (46 vs. 37%, respectively, P = 0.0125), but when maturity was evaluated again at 140 DAP, there was no significant difference between single and twin row plots (58 vs. 59% OBB, respectively). In 2022, maturity was sampled at 133, 144 and 158 DAP. In 2022, twin row plots overall had a greater percentage of OBB pods compared to single rows at 133 DAP (83 vs. 75%, respectively, P < 0.0001). The highest percentage of OBB pods was detected at the 144 DAP sampling time (86 vs. 79% at 133 DAP and 81% at 158 DAP, P = 0.0020). Plots treated with prohexadione calcium had a greater percentage of OBB pods in 2022 compared to untreated plots, regardless of row pattern or DAP (83 vs. 79%, respectively, P = 0.0090). When maturity results were pooled across years, twin row plots were more mature than single row plots (64 vs. 59%, respectively, P = 0.0209, Table 5). Twin row plots with prohexadione calcium treatment exhibited a greater percentage of OBB pods than untreated twins, or single rows with or without prohexadione calcium (P = 0.0366, Table 5). Across sampling dates, plots exhibited the greatest levels of maturity at 141 to 147 DAP. The interaction of growth regulator × sample date was significant (P = 0.0075), whereby prohexadione calcium treated plots at 133 DAP exhibited pod maturity greater than corresponding untreated plots at the same timing (65 vs. 58%) (Table 6). Treatment interactions did not significantly vary by cultivar (P > 0.15).

Table 5

Influence of row pattern and prohexadione calcium application on % orange, brown or black (OBB) pod maturity from later maturing cultivars from pooled experiments conducted in 2021 and 2022.

Table 6

Influence of digging date and prohexadione calcium application on % orange, brown or black (OBB) pods from later maturing cultivars from pooled experiments conducted in 2021 and 2022.

Average daytime temperature was greater in single row plots than corresponding twin row plots (29.6 vs. 29.1 C, respectively, P < 0.0001). The interaction of row pattern and cultivar was also significant (P = 0.0034), with either cultivar planted in twin rows having cooler temperatures (~29.1 C) compared to single rows of FloRun 331 (29.4 C) followed by Georgia-16HO (29.8 C). Temperatures additionally varied at the row pattern × prohexadione calcium × cultivar level with regard to approximate dates of 50% of row having lapped (P = 0.0495). Differences were not evident prior to rows lapping (P = 0.8928) for FloRun 331 but were recorded following rows lapping (P = 0.0112) where twin rows without prohexadione calcium application were cooler than single rows with or without prohexadione calcium treatment (25.9 vs. ~26.5 C, respectively); temperatures for FloRun 331 planted to twins with prohexadione calcium (26.3 C) were not different compared to twins or singles without application. Georgia-16HO daytime ground temperatures were different both prior to and following 50% rows lapping (P < 0.0005). Prior to rows lapping, single rows were overall warmer than twin row configurations. Following rows lapping, a similar pattern was evident as for FloRun 331, with twins exhibiting cooler temperatures (~26 C) than single rows, in addition to smaller single row canopies associated with prohexadione calcium treatment having been warmer than those without treatment (27.2 vs. 26.7 C, respectively).

Across pooled pod density results from 2021 and 2022, Georgia-16HO treated with prohexadione calcium exhibited a more taproot-focused pod set (0.01 to 0.04 smaller ratio from 10 to 90% pod pixels) than when prohexadione calcium was not applied, while FloRun 331 showed an inverse and smaller-magnitude (i.e., differences of 0.013 to 0.018) relationship across a narrower range of pod pixels (10 to 60%) (Figure 2; cultivar × prohexadione calcium application × % pod pixels interaction P = 0.0893). Additionally, twins with or singles without prohexadione calcium had the most taproot-focused crop from 20 to 70% of pod pixels, followed by singles with prohexadione calcium (i.e., 60 to 70% pod pixels), while twins without prohexadione calcium had the most limb-set crop (> 60% pod pixels, Figure 3; prohexadione calcium application × pattern × % pod pixels interaction P < 0.0001). Pod ratios for twin rows without prohexadione calcium were ~0.05 larger than twin rows with or single rows without treatment from 60 to 90% pod pixels.

Figure 2. Influence of prohexadione calcium (PC) application (“+” = applied, “-” = not applied) on the ratio of radii corresponding to % pod pixels : radii of total pixels in individual later maturing cultivars. FR331 = FloRun 331; Ga16HO = Georgia-16HO. Estimated means at the same % total pod pixels per cultivar followed by different letters are significantly different according to the method of Benjamini-Hochberg at α = 0.10.

Figure 3. Influence of row planting pattern and prohexadione calcium (PC) application (“+” = applied, “-” = not applied) on the ratio of radii corresponding to % pod pixels : radii of total pixels among pooled later maturing cultivars. Estimated means at the same % total pod pixels followed by different letters are significantly different according to the method of Benjamini-Hochberg at α = 0.10.

Pod yield was greater in twin row versus single row planted plots at P = 0.0018. Plots treated with prohexadione calcium overall yielded significantly less than untreated plots (4427 vs. 4594 kg/ha, respectively, P = 0.0865). The interaction of cultivar, row pattern and prohexadione calcium application was significant at P = 0.0774. FloRun 331 planted in twin rows without prohexadione calcium yielded significantly greater than single rows with or without prohexadione calcium application, whereas Georgia-16HO planted in twin rows with or without prohexadione calcium application or single rows without prohexadione calcium yielded greater than corresponding single rows treated with prohexadione calcium (Table 7). Individual year results and results combined across years and locations can be found in Table 7.

Table 7

Influence of row pattern and prohexadione calcium application on pod yield (kg/ha) from later maturing cultivars from experiments conducted in 2021 and 2022 at the Edisto Research and Education Center (EREC) and the Pee Dee Research and Education Center (PDREC).

At EREC in 2022, plots without prohexadione calcium treatment had a greater percentage of TSMK compared to those receiving prohexadione calcium (70 vs. 68% respectively, P = 0.0942). Conversely, both at EREC in 2021 and across the pooled data, there were no significant differences in TSMK observed among treatments. Nevertheless, twin row plots tended to have a slightly higher TSMK than single rows, as was observed in the early maturing group. At EREC in 2021, plots without prohexadione calcium had greater economic value than treated plots ($1410 vs. $1306 per hectare, respectively, at P = 0.0909). In contrast, in 2022 prohexadione calcium application was not significant regarding economic return at P = 0.2287. In 2022, single row planting pattern had a greater economic return when compared to twin rows ($1649 vs. $1565 per hectare, respectively, at P = 0.0675). When economic return values were combined across years, treatment effects did not significantly influence value.

Pod OBB maturity was negatively correlated with examined temperature variables (ρ = ~ -0.7 and ~ -0.6), positively correlated with main stem heights (ρ = 0.71 and 0.64), and somewhat positively correlated with pod radius ratios (ρ = 0.18 to 0.37) for both FloRun 331 and Georgia-16HO. Maturity was also somewhat positively correlated with pod yield for Georgia-16HO (ρ = 0.34). Main stem heights were negatively correlated with examined temperature variables and somewhat positively correlated with pod radius ratios and yield (Table 8). Increased temperatures were somewhat associated with a decrease in pod radius ratios for Georgia-16HO, though this was not consistent among FloRun 331 data. FloRun 331 pod yield was also somewhat positively correlated with pod radius ratios and TSMK (ρ = 0.2 to 0.4). When cultivar × row pattern × prohexadione calcium application level data were pooled across maturity group experiments, correlation coefficients of main stem heights with pod yield were significantly and negatively related to main stem height at the rate of -0.039 (P = 0.0008) (concordance correlation coefficient = 0.62; Figure 4).

Figure 4. Linear regression plot of cultivar × row pattern × prohexadione calcium application Spearman correlation coefficients of main stem height with pod yield as predicted by corresponding average main stem heights (cm). Slope = -0.039 (P = 0.0008); intercept = 1.52 (P = 0.0001); concordance correlation coefficient = 0.62. The shaded band is the estimated 90% confidence interval.

Table 8

Spearman correlation coefficients of variable^a measurements for FloRun 331 (above the diagonal) and Georgia-16HO (below the diagonal).

Discussion

The goal of this work was to evaluate the combined and independent effects of row planting pattern and prohexadione calcium application on the growth, maturity development and pod distribution of newer peanut cultivars that have recently been commercially planted in South Carolina. Corroborating earlier reports (Culbreath et al., 2008; Tillman et al., 2006), twin row planted stands typically exhibited less TSW incidence than single row planted stands.

Results from these experiments showed canopy architecture of both runner type and Virginia type peanut treated with prohexadione calcium to have consistently exhibited a more triangular shape than untreated peanut regardless of cultivar, year, or row planting pattern. This corroborated earlier studies that reported the change in canopy architecture following prohexadione calcium application at 50% row closure (Beam et al., 2002; Culpepper et al., 1997; Faircloth et al., 2005; Jordan et al., 2004, 2008, 2009; Mitchem et al., 1996; Studstill et al; 2020). Results of this experiment also supported previous reports that two applications of prohexadione calcium at 0.75× the label rate was efficient at significantly reducing main stem growth and increasing row visibility (Studstill et al., 2020). Results additionally detailed prohexadione calcium to have varying effects on canopy temperature. Among Virginia cultivar single rows and Georgia-06G twin rows, prohexadione calcium treatment reduced ground temperature (i.e., through increased shading). In those cases, this was not associated with a parallel significant effect on yield across the pooled data, though the Virginia cultivar yields exhibited a trend of being higher for treatments with cooler ground temperature with this having been more prominent at EREC in 2021. With respect to collective FloRun 331 and Georgia-16HO row patterns and Georgia-06G single rows, prohexadione calcium was conversely linked to increased ground temperatures. Although it is yet to be mechanistically determined as to the cause of the differing results among examined cultivars, which may or may not be related to unmeasured canopy architecture or density effects and subsequent modifications to balances of shading and insulation efficacies, within the FloRun 331 and Georgia-16HO data, the increased yields seen among some treatments in the absence of prohexadione calcium application may be a result of their correspondingly cooler ground temperatures. Results from the correlation analysis (and furthermore, the correlation-regression analysis) support temperature effects on pod yield as having varied by cultivar canopy size. Georgia-06G and Georgia-16HO overall exhibited smaller canopies than FloRun 331 and stronger positive correlations between main stem height and pod yield; this helps to explain their negative correlations between canopy temperature and yield having been significant whereas it was not significant for FloRun 331. Similarly, Virginia cultivars exhibited the largest canopies where main stem heights were no longer significantly correlated with pod yield; Virginia cultivars in turn were the only ones examined where canopy temperature was significantly yet slightly positively correlated with pod yield. Overall, plots planted in twin rows exhibited cooler daytime ground temperatures compared to single rows. While measuring pollen viability was not part of the scope of this study, the cooler overall temperatures and reduced proportion of days with maximum daytime canopy ground temperature > 36 C (e.g., as twin row planting increased main stem height which was in turn correlated with decreased temperatures) created a less stressful environment for fertilization and subsequent peg and pod development (Ketring 1984).

Twin row planting was associated with a greater amount of yield, % OBB and % TSMK. Twin row planting was greater in economic return when compared to single rows in the earlier maturing group. In the later maturing group, however, no significant difference in economic return was seen between twin and single row plots. The later maturing runner cultivars used, FloRun 331 and Georgia-16HO, have larger and bushier canopies than Georgia-06G, the runner cultivar used in the earlier maturing group. Thus, it is interesting that yield improvements were not observed for these cultivars when planted in twin rows in the presence of prohexadione calcium application.

In the small plot experiments (i.e., plot length = 30.5 m), prohexadione calcium application was not associated with a significant difference in yield in the earlier maturing group but generally resulted in a significant yield reduction in the later maturing experiment with pooled results showing a loss of 170 kg/ha following application. Conversely, in 2021 at the large on-farm experiment, prohexadione calcium application increased yield by 770 kg/ha. Studstill et al. (2020) reported a similar relationship in which prohexadione calcium treated small plots (~5.5 to 11 m in length) did not show significant yield differences, but large treated plots (~155 to 455 m in length) yielded significantly greater than untreated plots. While the plot size selected and used in the research plots of this study were intermediate in length according to the plot length groups reported by Studstill et al. (2020), they were closer in size to small plots than large plots. Multiple studies have found the influence of prohexadione calcium on yield to be inconsistent and cultivar dependent (Beam et al., 2002; Faircloth et al., 2005; Jordan et al., 2008, 2009), but reports have varied or not been explicit on the mechanism as to why this happens. Beam et al. (2002) reported up to 4% decrease in pod loss upon inversion in single row plots treated with prohexadione calcium when compared to untreated single rows, which they surmised was due to the gynophores being more strongly attached to the pod and axillary branch of the peanut. When single rows of Georgia-16HO were treated with prohexadione calcium, yield was significantly reduced, indicating that if prohexadione calcium does make gynophore attachment stronger, that is plausibly a cultivar-dependent effect.

Based on this research, both twin row planting pattern and prohexadione calcium independently influenced peanut to set pods significantly closer to the taproot, with results varying by cultivar group. Ortiz et al. (2013) reported that for every two centimeters a tractor operator deviates off the row center, yield losses of up to 186 kg/ha can be expected. If the rows are easier to distinguish and pods are located more centrally to the taproot, the yield increases associated with prohexadione calcium may simply or in part be due to greater digging and/or inversion efficiency. The pod distribution data presented is novel and contributes informative measurements, and the use of ratios allowed pod concentrations among varying total pod set areas to be compared. Unsurprisingly, the difference in pod pixel radius ratios for twins compared to singles (~3% for Georgia-06G or Virginia cultivars overall and ~2% for FloRun 331 or Georgia-16HO treated with prohexadione calcium) was less than the difference in intra-row seed spacing based on planter settings (i.e., single rows at 19 seed/m compared to 11.5 seed/m per individual twin corresponding to ~65% greater seed density among single rows). This was to be expected, as areas of pod set naturally extend beyond the point of sowing and subsequent taproot. Measuring pod distribution characteristics serves as an additional tool to characterize pod distribution effects and relationships in future studies. Furthermore, profiling pod distribution ratios across the range of pod set area allows for greater capture and examination of treatment responses (i.e., as opposed to examining differences or distributions at a single [relative] distance from the taproot).

Prohexadione calcium had variable effects on the percentage of TSMK, similar to previous reports (Beam et al., 2002; Culpepper et al., 1997; Mitchem et al., 1996; Monfort et al., 2021). Results from maturity samples indicated prohexadione calcium only caused a significant gain in % OBB pods in conjunction with twin row planting for the later maturing FloRun 331 and Georgia-16HO. Whereas this effect was not observed among the Virginia cultivar data in the present study, it was so reported for Virginia cultivars in single rows by Culpepper et al. (1997). This discrepancy may be explained by the different sample collection methods in how Culpepper et al.’s (1997) samples were obtained after mechanical inversion whereas those in the present study were manually collected via gently digging. The difference in approaches corresponds to sampling pods produced and available in the ground at the time of collection (manual digging) or only those available and retained on the plant following mechanical inversion, which is more aggressive. As a result, samples collected from mechanically prepared windrows would be subject to varying levels of interference from canopy-associated resistance as affected by examined treatments (i.e., prohexadione calcium application reduces main stem height which could contribute to less digger-related pod loss). In addition to twin planting overall, pod maturity of FloRun 331 or Georgia-16HO treated with prohexadione calcium was associated with greater pod maturity at 133, 141 to 147, and 158 DAP than at the same timings when prohexadione calcium was not applied, with this being significant at 133 DAP. Though the combining of 141 and 147 DAP sample timings from 2021 and 2022, respectively, facilitated comparison of interpretable groupings across independent years, it is possible the difference may have reduced the ability to detect a shorter yet viable length of time where treatments could have contributed maturity levels not different from later-assessed values (e.g., 7 days compared to the subsequent approximation of 11 days). Nevertheless, while corresponding benefits of prohexadione calcium application did not consistently translate over to improved yield for these two runner cultivars from the available (small plot) data, more importantly across cultivars, twin row planting with prohexadione calcium treatment did not result in decreased yields, and it moreover increased yield on the large on-farm test.

Based on results from this work, development of pod maturity was overall improved through the use of twin row planting for the three examined runner cultivars and its combined use with prohexadione calcium for FloRun 331 and Georgia-16HO. Maturity of Virginia cultivars was not significantly improved with examined treatments, although their twins were numerically more mature than corresponding singles. While the increased maturity seen among select treatments for runner cultivars (i.e., + ~6% for FloRun 331 or Georgia-16HO twins with prohexadione calcium or for Georgia-06G twins) was significant and thus represents improved maturity development, this would not be anticipated to automatically result in a ready reduction of a fungicide application toward the end of the growing season. Rates of pod maturity development prior to relative optimal economic value reported by Anco et al. (2024) translate the estimated magnitude of increased treatment maturity (e.g., 6%) as representing a time savings of approximately 5 days. Even so, any time potentially saved is potentially able to contribute to the possibility of reducing the need for such a fungicide application and, more importantly, an earlier harvest, as late-season application and harvest decisions depend on a variety of factors not limited to environmental conditions, cultivar susceptibility to diseases, canopy health, present and impending weather conditions, and logistical constraints (Anco et al. 2020, 2024; Jordan et al. 2016, 2019, 2024). Favorably contributing to the reduced-risk nature of such treatments with a potential for improved maturity is their innate compatibility with producer and practitioner capabilities to examine fields for pod maturity in evaluating digging decisions (Anco et al. 2024).

Gratitude is extended to Justin Hiers for technical assistance in establishing and maintaining plots. Sincere thanks to Madison Turnblad and Bubba Bamberg for cooperation with on-farm experiments. Support for research was provided by the South Carolina Peanut Board, National Peanut Board, and Georgia Seed Development. Technical Contribution No. 7333 of the Clemson University Experiment Station. This material is based upon work supported by NIFA/USDA, under project number SC-1700592.

Literature Cited

American Peanut Shellers Association. 2020. Farmers Stock Trading Rules.

Alderman S. C. and Nutter, Jr. F.W. 1994. Effect of temperature and relative humidity on development of Cercosporidium personatum on peanut in Georgia. Plant Dis., 78:690–694.

Anco D.J. 2023. Peanut disease management. Peanut money-maker 2023 production guide: 44-55.

Anco D.J. and Hiers J.B.. 2022. Pod yield production among peanut (Arachis hypogaea L.) cultivars in South Carolina. Peanut Sci. 49 (1):49-53.

Anco D.J., Kirk K.R., and Heirs J.B.. 2024. Revised thresholds for runner peanut harvest maturity pertaining to recent cultivars in South Carolina. Peanut Sci. 51 (1):8-17.

Anco D.J., Thomas J.S., Jordan D.L., Shew B.B., Monfort W.S., Mehl H.L., Small I.M., Wright D.L., Tillman B.L., Dufault N.S., Hagan A.K., and Campbell H.L.. 2020. Peanut yield loss in the presence of defoliation caused by late or early leaf spot. Plant Dis. 104:1390-1399.

Anco D.J., Thomas J.S., Marshall M., Kirk K.R., Plumblee M.T., Smith N., Farmaha B., and Payero J.. 2021. Peanut Money-Maker 2021 Production Guide. Clemson University Extension, Circular 588.

Baldwin J.A., Todd J.W., Weeks J.R., Gorbet D.W., Culbreath A.K., Luke-Morgan A.S., Fletcher S.M., and Brown S.L.. 2001. A regional study to evaluate tillage, row patterns, in-furrow insecticide, and planting date on the yield, grade and tomato spotted wilt virus incidence of the Georgia Green peanut cultivar. Proc. Annual Southern Conservation Tillage Conference Sustainable Agric. 24:26-34.

BASF. 2012. Apogee: Plant growth regulator booklet. Ontario, Canada.

Beam J.B., Jordan D.L., York A.C., Isleib T.G., Bailey J.E., McKemie T.E., Spears J.F., and Johnson P.D.. 2002. Influence of prohexadione calcium on pod yield and pod loss of peanut. Agronomy J., 94(2):331–336.

Benjamini Y., and Hochberg Y.. 1995. Controlling the false discovery rate: a practical and powerful approach to multiple testing. J. R. Statist. Soc. 57:289-300.

Boote K.J. 1982. Growth stages of peanut (Arachis hypogaea L.). Peanut Sci. 9 (1):35-40.

Branch W.D. 2007. Registration of ‘Georgia‐06G’ Peanut. J Plant Reg. 1(2): 120–120. https://doi.org/10.3198/jpr2006.12.0812crc.

Branch W.D. 2010. Registration of ‘Georgia-09B’ Peanut. J. Plant Reg. 4:175-178. https://doi.org/10.3198/jpr2009.12.0693crc.

Branch W.D. 2017. Registration of ‘Georgia-16HO’ Peanut. J Plant Reg. 11:231-234. https://doi.org/10.3198/jpr2016.11.0062crc.

Brooks M.E., Kristensen K., van Benthem K.J., Magnusson A., Berg C.W., Nielsen A., Skaug H.J., Maechler M., Bolker B.M.. 2017. glmmTMB balances speed and flexibility among packages for zero-inflated generalized linear mixed modeling. R J. 9:378-400.

Byers R.E., and Yoder K.S.. 1999. Prohexadione calcium inhibits apple, but not peach, tree growth, but has little influence on apple fruit thinning or quality. Hort. Sci. 34:1205– 1209.

Chapin J.W., and Thomas J.S.. 2005. Effect of fungicide treatments, pod maturity, and pod health on peanut peg strength. Peanut Sci. 32(2):119–125.

Colvin B.C., Rowland D.L., Ferrell J.A., and Faircloth W.H.. 2014. Development of a digital analysis system to evaluate peanut maturity. Peanut Sci., 41 (1):8–16.

Culpepper A.S., Jordan D.L., Batts R.B., and York A.C.. 1997. Peanut response to prohexadione calcium as affected by cultivar and digging date. Peanut Sci. 24(2):85–89.

Culbreath A.K., Tillman B.L., Gorbet D.W., Holbrook C.C., and Nischwitz C.. 2008. Response of new field resistant peanut cultivars to twin row pattern or in-furrow applications of phorate insecticide for management of spotted wilt. Plant Dis. 92:1307-1312.

Davidson J.I., Blankenship P.D., Henning R.J., Guerke W.R., Smith R.D., and Cole R.J.. 1991. Geocarposphere temperature as it relates to Florunner peanut production. Peanut Sci. 18 (2):79-85.

Faircloth J.C., Coker D.L., Swann C., Mozingo W., Phipps P.M., and Jordan D.L.. 2005. Response of four Virginia-type peanut cultivars to prohexadione calcium as affected by cultivar and planting pattern. Peanut Sci. 32 (1):42-47.

Grossman K., Koenig K.S., and Kwiatkowski J.. 1994. Phytohormonal changes in intact shoots of wheat and oilseed rape treated with the acylcyclohexanedione growth retardant prohexadione calcium. Physiologia Plantarum 90 (1):139–143.

Haynes J.M., Smith N., Culbreath A.K., Kirk K.R., and Anco D.J.. 2019. Effects of insecticides applied with in-furrow with superabsorbent polymer on peanut cultivars infected with tomato spotted wilt virus. Peanut Sci. 46(2):127-139.

Jordan D.L., Anco D., Balota M., and Brandenburg R.L.. 2024. Farmer insights on harvesting peanut: A survey from the Virginia-Carolina region of the United States. Crop Forage Turfgrass Manag. 10:e20262.

Jordan D.L., Beam J.B., Lanier S.H., and Johnson P.D.. 2004. Peanut (Arachis hypogaea L.) response to cyclanilide and prohexadione calcium. Peanut Sci. 31 (1):33-36.

Jordan D.L., Hare A.T., Roberson G.T., Ward J., Shew B.B., Brandenburg R.L., Anco D., Thomas J., Balota M., Mehl H., and Taylor S.. 2019. Survey of practices by growers in the Virginia-Carolina region regarding digging and harvesting peanut. Crop Forage Turfgrass Manag. 5:1-4.

Jordan D.L., Nuti R.C., Beam J.B., Lancaster S.H., Lanier J.E., and Johnson P.D.. 2009. Influence of application variables on peanut (Arachis hypogaea L.) response to prohexadione calcium. Peanut Sci. 36 (1):96-103.

Jordan D.L., Nuti R.C., Beam J.B., Lancaster S.H., Lanier J.E., Lassiter B.R., and Johnson D.E.. 2008. Peanut (Arachis hypogaea L.) cultivar response to prohexadione calcium. Peanut Sci. 35 (2):101-107.

Jordan D.L., Shew B.B., and Johnson D.J.. 2016. Response of peanut cultivar (Arachis hypogaea L.) cultivar Gregory to interactions of digging date and disease management. Advances Agric. 2016:1–9.

Jordan D.L., Spears J.F., and Sullivan G.A.. 1998. Influence of digging date on yield and gross return of Virginia-type peanut cultivars in North Carolina. Peanut Sci. 25(1):45-50.

Ketring D.L. 1984. Temperature effects on vegetative and reproductive development of peanut. Crop. Sci. 24:877-882.

Kirk K.R. Load Image Processor Batch; v.1.1.; Clemson University: Clemson, SC, USA, 2022.

Lanier J.E., Jordan D.L., Spears J.F., Wells R., Johnson P.D., Barnes J.S., Hurt C.A., Brandenburg R.L., and Bailey J.E.. 2004. Peanut response to planting pattern, row spacing, and irrigation. Agronomy J. 96(4):1066–1072.

Lee I.J., Foster K.R., and Morgan P.W.. 1998. Effect of gibberellin biosynthesis inhibitors on native gibberellin content, growth and floral initiation in Sorghum bicolor. J. Plant Growth Regulators, 17:185– 195.

Mitchem W.E., York A.C., and Batts R.B.. 1996. Peanut Response to Prohexadione Calcium, a New Plant Growth Regulator. Peanut Sci. 23(1):1-9.

Monfort W.S., Tubbs R.S., Cresswell B., Jordan E., Smith N., and Luo X.L.. 2021. Yield and economic response of peanut (Arachis hypogaea L.) cultivars to prohexadione calcium in large-plot trials in Georgia. Peanut Sci. 48(1):15-21.

Mozingo R.W., Coffelt T.A., and Wright F.S.. 1991. The influence of planting and digging dates on yield, value, and grade of four Virginia-type peanut cultivars. Peanut Sci. 18 (1):55–62.

Nakayama I., Kobayashi M., Kamiya Y., Abe H., and Sakurai A.. 1992. Effects of a plant-growth regulator, prohexadione-calcium (BX 112), on the endogenous levels of gibberellins in rice. Japanese Soc. Plant Physiology, 33:59– 62.

Nuti R.C., Faircloth W.H., Lamb M.C., Sorenson R.B., Davidson J.L., and Brenneman T.B.. 2008. Disease management and variable planting patterns in peanut. Peanut Sci. 35 (1):11-17.

Ortiz B.V., Balkcom K.B., Duzy L., van Santen E., and Hartzog D.L.. 2013. Evaluation of agronomic and economic benefits of using RTK-GPS-based auto-steer guidance systems for peanut digging operations. Precision Agric. 14:357-375.

Core Team R. 2023. R: A language and environment for statistical computing, R Foundation for Statistical Computing: Vienna, Austria. Available online: https://www.R-project.org/ (accessed on 1 November 2023).

Renfroe-Becton H., Kirk K.R., and Anco D.J.. 2022. Using image analysis and regression modeling to develop a diagnostic tool for peanut foliar symptoms. Agronomy, 12:2712. DOI: [: 10.3390/agronomy12112712].

Sanders T.H., Blankenship P.D., Vercellotti J.R. and Crippen K.L.. 1990. Interaction of curing temperature and inherent maturity distributions on descriptive flavor of commercial grade sizes of Florunner peanuts. Peanut Sci. 17 (2):85-89.

Sanders T.H., Vercellotti J.R., Blankenship P.D., Crippen K.L., and Civille G.V.. 1989. Interaction of maturity and curing temperature on descriptive flavor of peanuts. J. Food Sci. 54 (4):1066-1069.

Sorenson R.B., Lamb M.C., and Butts C.L.. 2007. Peanut response to row pattern and seed density when irrigated with subsurface drip irrigation. Peanut Sci. 34 (1):27–31.

Sorenson R.B., Lamb M.C., and Butts C.L.. 2015. Can peg strength be used as a predictor for pod maturity and peanut yield? Peanut Sci. 42 (2):92–99.

Sorenson R.B., Sconyers L.E., Lamb M.C., and Sternitzke D.A.. 2004. Row orientation and seeding rate on yield, grade, and stem rot incidence of peanut with subsurface drip irrigation. Peanut Sci. 31(1):54-58.

Studstill S.P., Monfort W.S., Tubbs R.S., Jordan D.L., Hare A.T., Anco D.J., Sarver J.M., Ferguson J.C., Faske T.R., Creswell B.L., and Tyson W.G.. 2020. Influence of prohexadione calcium rate on growth and yield of peanut (Arachis hypogaea). Peanut Sci. 47(3):163–172.

Tillman B.L. 2018. Registration of ‘TUFRunner ‘297’’ Peanut. J. Plant Reg. 12:31-34. https://doi.org/10.3198/jpr2017.02.0007crc.

Tillman B.L. 2021. Registration of ‘FloRun ‘331’’ Peanut. J. Plant Reg. 15:294-299. https://doi.org/10.1002/plr2.20141.

Tillman B.L., Gorbet D.W., Culbreath A.K., and Todd J.W.. 2006. Response of peanut cultivars to seeding density and row patterns. Crop Manag. Research, 5 (1). https://doi-org.libproxy.clemson.edu/10.1094/CM-2006-0711-01-RS.

Tubbs R.S., Beasley J.P., Culbreath A.K., Kemerait R.C., Smith N.B., and Smith A.R.. 2011. Row pattern and seeding rate effects on agronomic, disease, and economic factors in large-seeded runner peanut. Peanut Sci. 38(2):93–100.

USDA FSA. 2019. Peanut Buyers and Handlers Program Guidelines for 2019 and Subsequent Crop Years. 1–15.

USDA FSA. 2021. Peanut Premiums and Discounts for 2021 Crop Year. Available at: https://www.fsa.usda.gov/Assets/USDA-FSA-Public/usdafiles/Price-Support/pdf/2021/2021-Peanut%20Premiums%20and%20Discounts.pdf.

USDA FSA. 2022. Peanut Premiums and Discounts for 2022 Crop Year. Available at: https://www.fsa.usda.gov/Assets/USDA-FSA-Public/usdafiles/Price-Support/pdf/2022-Peanuts/2022-Peanut%20Premiums%20and%20Discounts.pdf.

Wehtje G., Walker R.H., Patterson M.G., and McGuire J.A.. 1984. Influence of twin rows on yield and weed control in peanuts. Peanut Sci. 11(2):88-91.

Williams E.J. and Drexler J.S.. 1981. A non-destructive method for determining peanut pod maturity. Peanut Sci. 8(2):134-141.

Wright F.S. and Porter D.M.. 1991. Digging date and conservational tillage influence on peanut production. Peanut Sci. 18(2):72-75.

Yamaji H., Katsura N., Nishijima T., and Koshioka M.. 1991. Effects of soil-applied uniconazole and prohexadione calcium on the growth and endogenous gibberellin content of Lycopersicon esulentum Mill. seedlings. J. Plant Phys. 138:763– 764.