Hort. Series # 238

Principal Investigators: Jonathan R. Schultheis, Professor and Extension Specialist; Keith D. Starke, Agricultural Research Associate, Central Crops Research Station; Stuart W. Michel, Research Technician, Department of Horticultural Science, NC State University, Department of Horticultural Science

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We gratefully acknowledge the assistance of Hunter Barrier (Superintendent) and Wesley Hairre (Horticulture Supervisor), Horticultural Crops Research Station, Clinton, NC, as well as the personnel at the research station for their help in establishing, maintaining, and harvesting the cultigen evaluation studies. We want to acknowledge the following summer employees for their assistance with the studies: Benjamin Indermaur, Tanner Seay, Grayson Parrish, Samantha Mowery, and Cady Bailey. The cooperation and support of BASF/Nunhems; Enza Zaden; Hazera; Origene Seeds; Sakata Seed Company; Seminis; Syngenta and VoloAgri were also appreciated.

General Cultural Practices

These watermelon studies were grown on black plastic mulch and fertigated with drip tube. Pesticides used on all plots were chemicals labeled for that crop in the 2021 North Carolina Agricultural Chemicals Manual.

Disclaimer

This publication presents data from the triploid standard size and mini watermelon cultigen evaluation studies conducted during 2021. Information in this report is believed to be reliable but should not be relied upon as a sole source of information. Limited accompanying detail is included but excludes some pertinent information, which may aid interpretation.

Watermelon Cultural Practices for 2021 Cultigen Studies, Horticultural Crops Research Station, Clinton, NC

Introduction

Growing conditions for the 2021 watermelon studies were generally favorable for the first 8 weeks after planting, then conditions were very wet for the following 6 weeks. North Carolina showed an increase in watermelon production from 2019 to 2020. In 2019, acreage was reported at 7,800 acres. In 2020, acreage was reported at 9,000 acres. North Carolina ranks 7th among watermelon producing states and represents 9% of the U.S. acreage which totaled 100,000 acres in 2020. This translates into an economic value of $34 million to North Carolina. North Carolina also saw an increase in watermelon prices; $14.10 per cwt in 2019 to $15.80 per cwt in 2020. (North Carolina Agricultural Statistics) (USDA Vegetables 2020 Summary).

Materials and Methods

Sowing and Field Preparations – Standard and Mini Size Watermelon Studies

Once all seeds were received from participating companies, they were planted into 72 cell Poly trays to grow transplants (Hummert Int.; Earth City, MO). Seeds of standard and mini size cultigens were sown on 3 April 2021. The trays of sown seeds were placed in a germination room for about one day. Temperature in the germination room averaged about 85℉ and moisture was elevated to around 70%. The planting medium used was a “fine germinating mix”, a commercial soilless mix (SunGro, Agawam, MA). Approximately 3 weeks after seeding, transplants were placed in a “hardening” greenhouse for approximately one week before being transplanted in the field. Telone II (12 gal/ac) was applied to the entire study area on 9 March 2021. Roundup Original Max (1 qt/ac), K-Mag fertilizer (0-0-22-22-11Mg) at 200 lb/ac, and NPK fertilizer (10-10-10-0) at 500 lb/ac was applied pre-plant 8 April 2021. K-Mag fertilizer (0-0-22-22-11Mg) at 200 lb/ac was also applied after transplant on 30 April 2021. Black polyethylene plastic (1.25 mil thick, high density plastic film, 60 inches wide; TriEst Ag Group, Inc., Clinton, NC) was laid on 15 April 2021. Sandea (.75 oz/ac) and Strategy (3 pt/ac) were applied to row middles 26 April 2021.

Planting – Standard Size Watermelon Study

Standard size triploid watermelon plants were established in the field on 29 April 2021. Plot size for standard size triploid watermelons was 1 row, 10 plants per plot, 25 feet long with alleys of 10 feet between plots. In most cases, plots with missing plants were replanted approximately 3 days after planting to achieve 100% plant stand. ‘SP-7’ and ‘Wild Card Plus’ diploid pollenizer plants were used in the 2021 growing season. Alternate plantings of ‘SP-7’ and ‘Wild Card Plus’ (4 plants/plot) were used as the pollenizer plants in each plot within the study. ‘SP-7’ pollenizer plants were planted after triploid plants 1 and 7 while ‘Wild Card Plus’ pollenizer plants were planted after triploid plants 4 and 10 in each plot. Row middles were 10 feet and in-row spacing was 2.5 feet for the standard size triploid watermelon study.

Fertilizer and Pest Management – Standard and Mini Size Watermelon Studies

A total of 50 lb/ac N, 50 lb/ac P, 94 lb/ac K, 44 lb/ac S, and 44 lb/ac Mg were all applied broadcast (pre-plant) to the entire study area. Drip tape (NETAFIM, 12 in spacing, 0.24 gph; NETAFIM, Tel Aviv, Israel) was installed beneath the plastic mulch and was utilized to fertigate the crop throughout the growing season. Liquid fertilizer with 4-0-8 analysis was initially applied through drip tape fertigation on 5 May 2021 and similarly on the following dates: 11, 17, 19, 25, and 27 May 2021; 1, 7, 9, 14, 17, 22, 23, and 28 June 2021; 13, 16, and 26 July 2021. A total of 91 lb/ac N, 0 lb/ac P and 183 lb/ac K were applied via fertigation throughout the growing season. Cumulative totals of applied fertilizer for the growing season were: 141 lb/ac N, 50 lb/ac P, 321 lb/ac K, 88 lb/ac S and 44 lb/ac Mg.

Fungicides were initially applied on 28 May 2021 and similarly on the following dates: 9, 18 and 25 June 2021; 1, 16, and 30 July 2021. The following fungicides were rotated to avoid potential development of resistance from diseases; Bravo (1 qt/ac), Copper (1 lb/ac), Manzate (3 lb/ac), Presidio (4 oz/ac), Quadris (14 oz/ac and 15 oz/ac), Ranman (2.5 oz/ac), Luna Experience (8 oz/ac), Proline (4 oz/ac) and Tanos (6 oz/ac).

Insecticides Carbaryl (1 qt/ac) and Asana (8 oz/ac) were rotated and applied as a preventive measure on the following dates: 13, 19, and 28 May 2021; 18 and 25 June 2021. Asana (8 oz/ac) applications continued 1, 16 and 30 July 2021. Admire (10 oz/ac) was applied with the first application of Asana (8 oz/ac) on 13 May 2021. Insecticide products were sprayed in rotation to avoid potential development of insect resistance.

Miticide Portal (1 qt/ac) was applied on 5 May 2021. Applications of Gramoxone (1 qt/ac) plus crop oil (1 qt/ac) was spot sprayed on weed escapes on 20 May and 17 June 2021.

Harvest and Yield Data Collection – Standard Size Watermelon Study

Standard size triploid watermelon harvests took place on: 13, 20, and 28 July 2021. For the triploid standard size watermelon test, fruits were placed in the following categories: < 9 lb, 9 – 13.4 lb, 13.5 – 17.4 lb, 17.5 – 21.4 lb, and ≥ 21.5 lb. Fruits were considered marketable if they weighed 9.0 lb or more. Fruits are often commercially marketed by number or count per bin with 9.0-13.5 lb fruit termed 60-count, 13.6 – 17.5 lb fruit termed 45 count, 17.6 – 21.4 lb fruit termed 36-count, and fruit 21.5 lb or larger termed 30-count. We used these weight designations to categorize the harvested fruits in this study. Most of the standard size triploid watermelon fruit harvested in this study ranged between 17.5 and 21.4 lb.

Planting, Harvest and Yield Data Collection – Mini Sized Watermelon Study

The mini triploid watermelon transplants were established in the field on 29 April 2021. Plot size for mini triploid size watermelons was 1 row, 10 plants per plot, 15 feet long with alleys of 9 feet between plots. Alternate plantings of ‘SP-7’ and ‘Wild Card Plus’ (4 plants/plot) were used as the pollenizer plants in this study. ‘SP-7’ pollenizer plants were planted after triploid plants 1 and 5 while ‘Wild Card Plus’ pollenizer plants were planted after triploid plants 3 and 7. Row middles were 10 feet and in-row spacing was 1.5 feet for the mini size triploid watermelons.

Mini triploid watermelon harvests occurred on: 15, 22, and 29 July 2021 and 6 August 2021. For the 4 mini triploid watermelon harvests, fruits were placed in the following categories: < 3 lb, 3 – 7 lb, 7.1 – 9 lb, and ≥ 9.1 lb. Most of the mini size triploid watermelon fruit harvested in this study ranged between 3 and 7 lb.

Quality Evaluations – Standard and Mini Size Watermelon Studies

Evaluations of each melon entry included: yield, fruit size, fruit shape, soluble solids, and interior flesh firmness. Soluble solids were measured by cutting a piece of fruit from the center of the fruit and squeezing out the fruit juice onto the digital refractometer (Atago, Vernon Hills, IL). Flesh firmness was taken by using a Penetrometer FT 011 with a 7/16” plunger tip, (QA Supplies LLC, Norfolk, VA.), and was recorded in pounds. Samples were obtained by cutting the center of the fruit from the stem to blossom end. Pressure was then taken in five areas of the fruit: stem end, top side, ground spot side, blossom end, and center. The reported measures on flesh firmness are an average of the five sample areas and are an average value taken for 3 fruit per plot or 12 fruits per cultigen. Pressure was not taken on fruit with hollow heart. Hard seed in triploid fruit was determined according to the USDA standards. Fruits were cut longitudinally in half, and then these halves were cut laterally. The number of hard seeds exposed on the cut surface were counted and recorded. Most of the quality measurements were taken at the first and second harvests. Additional internal evaluations included hollow heart incidence and severity, flesh color, seed trace, hard seed population, and rind thickness.

Results

Overall fruit yield and quality were very good for the duration of the study. It should be noted that precipitation during harvests was high at the Horticultural Crops Research Station in Clinton, NC; 12.46 inches in July of 2021 (State Climate Office of North Carolina, Station: Horticultural Crops Research Stn (CLIN)). These high moisture conditions caused the fruit in later harvests to be more susceptible to rot. Rots comprised 4% of fruit in the cumulative standard triploid watermelon harvests and 3% of fruit in the cumulative mini triploid watermelon harvest. Bird pecks were also an issue in the early harvests. There was incidence of fusarium wilt caused by Fusarium oxysporum f.sp. niveum in some of the watermelon plots, however, the impact on the fruit and vines was generally negligible. A representative photograph of each cultigen entry is shown for the standard size cultigens and mini size cultigens (Figure 2), the exception being ‘Talca’.

Standard Size Watermelon Study – Yield and Size

The highest yielding standard size triploid cultigens for marketable fruit in the early harvest (1) were Sweet Gem (258 cwt/ac), Dark Knight (244 cwt/ac), and Excursion (220 cwt/ac). The average marketable yield for the early harvest (1) was 129 cwt/ac. There was a lot of variability between plots. At a significance level 0.05, the LSD was 189 for marketable fruit weights. Talca was the highest yielding standard size triploid cultigen for marketable fruit in the late harvest (3) (425 cwt/ac) (Table 2). The second highest yielding was Embasy (321 cwt/ac) followed by Lajoya (307 cwt/ac). The average marketable yield for the late harvest (3) was 228 cwt/ac. Talca was the highest yielding cultigen in the late harvest (3) (425 cwt/ac) but the lowest yielding in the early harvest (1) (32 cwt/ac). Dark Knight was the second highest yielding in the early harvest (1) (244 cwt/ac) but the lowest yielding in the late harvest (3) (91 cwt/ac).

Marketable yields across all three standard size triploid harvests were greatest for Summerlicious (854 cwt/ac), Shoreline (800 cwt/ac), and Sierra Nevada (756 cwt/ac) (Table 3). The average marketable yield across all harvests was 676 cwt/ac. Of the WDL lines, WDL 8415 (Valor) had an above average marketable yield (710 cwt/ac).

The standard size triploid cultigens with the highest average fruit weight in the early harvest (1) were WDL 9450 (24.8 lb/fruit), Sierra Madre (24.6 lb/fruit), and Sierra Nevada (23.5 lb/fruit). The average fruit size for the early harvest (1) was 19.8 lb/fruit. The standard size triploid cultigens with the highest average fruit weight in the late harvest (3) were Sierra Madre (20.3 lb/fruit), Scarlet Crisp (19.9 lb/fruit), and Sierra Nevada (19.7 lb/fruit). The average fruit size for the late harvest (3) was 16.6 lb/fruit, which was 3.2 lb/fruit less than the early harvest (1).

Average fruit weight across the three standard size triploid harvests were greatest for Sierra Madre (23.0 lb/fruit), Scarlet Crisp (22.8 lb/fruit), and Sierra Nevada (22.3 lb/fruit). The cultigens with the lowest average fruit wight across all harvests were Lajoya (14.8 lb/fruit), SVWA 6576 (15.7 lb/fruit), and Captivation (16.5 lb/fruit). The average fruit weight for all cultigens across all three harvests was 18.5 lb/fruit. It is worth noting that Sierra Madre and Sierra Nevada both consistently produced large fruit in the early and late harvests.

The standard size triploid cultigens with the highest fruit number per plant in the early harvest (1) were Dark Knight (0.8 fruit/plant), Sweet Gem (0.8 fruit/plant), and Red Amber (0.6 fruit/plant). The average fruit number per plant for the early harvest (1) was 0.4 fruit/plant. The standard size triploid cultigens with the highest fruit number per plant in the late harvest (3) were Talca (1.5 fruit/plant), Lajoya (1.4 fruit/plant), E26C.00124 (Destination) (1.1 fruit/plant), and ORS.6132C (1.1 fruit/plant) (Table 8). The average fruit number per plant for the late harvest (3) was 0.8 fruit/plant.

Fruit number per plant across all standard size triploid harvests were the greatest for Lajoya (2.7 fruit/plant), Summerlicious (2.7 fruit/plant), ORS.6132C (2.5 fruit/plant), and Talca (2.5 fruit/plant). The average fruit number per plant across all harvest was 2.1 fruit/plant.

The standard size triploid cultigens with the highest total marketable fruit number per acre were Summerlicious (4574 fruit/ac), ORS.6132C (4269 fruit/ac), and Lajoya (4225 fruit/ac). The standard size triploid cultigens with the lowest total marketable fruit number per acre were Excursion (2919 fruit/ac), WDL 9454 (2962 fruit/ac), WDL 9450 (2962 fruit/ac), and Sierra Madre (3006 fruit/ac). Average marketable fruit per acre was 97% across all entries for the season. The number of bins in the 60-count (9.0 – 13.5 lb), 45-count (13.6 – 17.5 lb), 35-count (17.5 – 21.4 lb), and 30-count (≥ 21.5 lb) bins are provided for harvest 1, harvest 2, harvest 3, and cumulatively for harvests 1, 2, and 3, respectively.

Standard Size Watermelon Study – Quality

Interior fruit quality measurements were taken across all standard size triploid harvests (most measurements were taken in the first or second harvest) and included: soluble solids, flesh color, seed trace size, length and diameter, rind thickness, flesh firmness, and hollow heart rating. The standard size triploid cultigens with the highest Brix readings were Talca (12.8), SVWA 6576 (12.6), and 7197 (12.5). The cultigen with the lowest Brix readings was Scarlet Crisp (10.9). The average Brix reading across all standard triploid cultigens was 12.0. The standard size triploid cultigens with the highest flesh firmness ratings were Shoreline (4.8), Scarlet Crisp (4.4), and WDL 8425 (3.8). The standard size triploid cultigens with lowest flesh firmness ratings were Sweet Gem (2.3), Dark Knight (2.5), Power House (2.5), and WDL 8415 (Valor) (2.5). The average flesh firmness rating across all standard size triploid cultigens was 3.0. There was a low incidence of hollow heart across all cultigens with 91% rating HH0 (no crack in flesh).

Mini Size Watermelon Study – Yield and Size

The highest yielding mini size triploid cultigens for marketable fruit weight in the early season harvests (1-2) were Sugar Bomb (462 cwt/ac), 50035 (393 cwt/ac), and Petite Perfection (350 cwt/ac). The average marketable yield for the early harvests (1-2) was 288 cwt/ac. Several of the cultigens had fruit that exceeded marketable size (> 9.1 lb). The highest yielding mini size triploid cultigens for marketable fruit in the mid-late season (3-4) were Sirius (166 cwt/ac), 50035 (157 cwt/ac), and Extazy (112 cwt/ac) (Table 12). The average marketable yield for the mid-late harvest (3-4) was 103 cwt/ac. Marketable yields for all mini size triploid cultigens were higher in the early season harvests (1-2) (288 cwt/ac) versus the mid-late season harvests (3-4) (103 cwt/ac) (Table 12).

Marketable yields across all (4 total) mini size triploid harvests were greatest for Sugar Bomb (567 cwt/ac), 50035 (550 cwt/ac), and Petite Perfection (456 cwt/ac) (Table 13). The mini size triploid cultigens with the lowest marketable yield across all harvests were ORS 7220 (242 cwt/ac), ORS 70368 (256 cwt/ac), and ORS 70383 (277 cwt/ac). The average marketable yield across all harvests was 391 cwt/ac. The majority of fruit were in the 3.1-7.0 lb category, with an average of 240 cwt/ac in this category across all harvests.

The mini size triploid cultigens with the highest average marketable fruit weight in the early season harvests (1-2) were ORS 7220 (7.2 lb), Extazy (7.0 lb), and Sugar Rush (7.0 lb) (Table 11). The average marketable fruit weight in the early harvests (1-2) was 6.6 lb. The mini size triploid cultigens with the highest average marketable fruit weight in the mid-late season harvests (3-4) were ORS 70368 (6.4 lb), Sirius (5.3 lb), and ORS 7220 (5.2 lb) (Table 12). The average marketable fruit weight in the mid-late season harvests (3-4) was 5 lb.

The mini size triploid cultigens with the highest average marketable fruit weight across all harvests were ORS 7220 (6.7 lb), ORS 70368 (6.6 lb), and Excite (6.3 lb) (Table 13). The cultigens with the lowest average marketable fruit weight were Sugar Bomb (5.3 lb), Petite Perfection (5.4 lb), and 50035 (5.8 lb). The average marketable fruit weight across all harvests was 6 lb. In general, fruit size was large for the 2021 growing season.

The mini size triploid cultigens with the highest fruit number per plant in the early season harvests (1-2) (Table 14) and across all four harvests (Table 15) were Sugar Bomb, Excite, and Preakness. The average fruit number per plant for the early season harvests (1-2) was 2.3 fruit/plant while the average fruit number per plant across all harvests (4) was 3 fruit/plant. The mini size triploid cultigens with the highest fruit number per plant in the mid-late season harvests (3-4) were Sugar Bomb (1.6 fruit/plant), 50035 (1.3 fruit/plant), and Sirius (1.1 fruit/plant). The average fruit number per plant for the mid-late season harvests (3-4) was 1.0 fruit/plant.

The mini size triploid cultigens with the highest total marketable fruit number per acre were Sirius (10600 fruit/ac), 50035 (9511 fruit/ac), and Petite Perfection (8494 fruit/ac). Average marketable fruit per acre was 72% across all entries for all four harvests. The main reason that fruit were not marketable was because of large fruit size (≥ 9.1 lb).

Percent of fruit weight per acre by size category are provided for early harvests (1-2), mid-late season harvests (3-4), and cumulative harvests (1-4), are available upon request.

Percent of fruit number by size category are available for early harvests (1-2), mid-late season harvests (3-4), and cumulative harvests (1-4), are available upon request.

Percent of total fruit weight and number per acre for harvests 1 and 2 and harvests 3 and 4. Most mini size triploid fruit were harvested in the first two harvests are available upon request.

Mini Size Watermelon Study – Quality

Interior fruit quality measurements were taken across all mini triploid harvests (nearly all measurements were taken in the first harvest) and included: soluble solids, flesh color, seed trace size, length and diameter, rind thickness, flesh firmness, and hollow heart rating. The mini size triploid cultigens with the highest Brix readings were Sirius (12.7), Petite Perfection (12.5), and Extazy (12.2) . The mini size triploid cultigen with the lowest Brix reading was Sugar Bomb (10.4). The average Brix reading across all cultigens was 11.8. The mini size triploid cultigen with the highest flesh firmness rating was ORS 70383 (4.0). The mini size triploid cultigen with the lowest flesh firmness rating was Preakness (2.7). The average flesh firmness rating across all cultigens was 3.3. There was a low incidence of hollow heart across all cultigens with 88.9% rating HH0 (no crack in flesh).

Summary

Overall, yields and fruit quality in this study were excellent. Good growing conditions and minimal pest pressure were important factors that contributed to these results.

Financial Support

In addition to seed companies this research was supported by the College of Life and Agricultural Sciences, North Carolina Agriculture Research, and the North Carolina Cooperative Extension Services. This work was in part supported by the National Institute of Food and Agriculture, U.S. Department of Agriculture, under award number 2020-51181-32139 for the CucCAP grant.