Hort. Series #241

Principal Investigators: Jonathan R. Schultheis, Professor and Extension Specialist, Department of Horticultural Science, NC State University; Stuart W. Michel, Research Technician, Department of Horticultural Science, NC State University; Baker E. Stickley, Research Technician Support, Department of Horticultural Science, NC State University.

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Acknowledgements

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 summer employees Andrew Pfefferkorn and Kaleb Holder, as well as graduate student Kim Heagy for their assistance with this study. The cooperation and support of BASF/Nunhems; Enza Zaden; HM Clause; Origene Seeds; Rijk Zwaan; Sakata Seed Company; Seedway; Seminis and Syngenta 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, (2022 North Carolina Agricultural Chemicals Manual).

Disclaimer

This publication presents data from the triploid standard size watermelon cultigen evaluation study conducted during 2022. 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 2022 Cultigen Studies, Horticultural Crops Research Station, Clinton, NC

Introduction

Growing conditions for the 2022 watermelon studies were favorable for the entire growing season. Temperatures were high and rainfall occurred in a timely manner and was never excessive during June through August (Figure 1). Rainfall was minimal during harvests 2 through 5 and watering was optimized through drip irrigation. Due to these favorable conditions, disease was not a factor and six harvests were made. The number of harvests in this study was comparable to the number of harvests and excellent markets that were experienced by commercial growers in North Carolina. North Carolina showed a small increase in watermelon production from 2020 to 2021. In 2020, acreage was reported at 9,000 acres. In 2021, acreage was reported at 9,300 acres. This translates to an economic value of $36 million to North Carolina in 2021. North Carolina also saw a decrease in watermelon prices; $14.10 per cwt in 2021 from $15.80 per cwt in 2020 (USDA 2021 State Agriculture Overview, North Carolina).

Materials and Methods

Sowing and Field Preparations

Telone II (12 gal/ac) was applied to the entire study area on 4 March 2022 for weed and nematode control. K-Mag fertilizer (0-0-22-22-11Mg) at 150 lb/ac and NPK fertilizer (10-10-10-0) at 500 lb/ac were applied pre-plant on 29 March 2022.

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 size cultigens were sown on 31 March 2022 (27 flats). Entry ‘Cracker Jack’ was received 13 days later than the other entries and was seeded 13 April 2022. The trays of sown seeds were placed in a germination room for 1-2 days. Temperature in the germination room was kept at 90-95 °F and humidity was kept between 85-90%. The planting medium used was a “fine germinating mix”, a commercial soilless mix (SunGro, Agawam, MA). Transplants were moved to a greenhouse for approximately three weeks, then moved to a “hardening” greenhouse for one week before being transplanted in the field.

Black polyethylene plastic (1.25 mil thick, high density plastic film, 60 inches wide; TriEast Ag Group, Inc., Clinton, NC) was laid on 22 April 2022. Command 3ME (0.5 pt/ac) and Curbit (4 pt/ac) were applied to row middles pre-plant on 3 May 2022.

Planting

Standard size triploid watermelon transplants were established in the field on 5 May 2022. Plots were 25 ft, 10 plants per plot, with 10 ft alleys between plots. Plots with missing plants were replanted 1 week after planting to achieve 100% plant stand. ‘SP-7’ and ‘Wingman’ diploid pollinizer plants were used in the 2022 growing season to take advantage of the disease resistance and flowering habit of the complementary cultivars. Alternate plantings of ‘SP-7’ and ‘Wingman’ (4 plants/plot) were used as the pollenizer plants in each plot. ‘SP-7’ pollenizer plants were planted following triploid plants 1 and 7 while ‘Wingman’ pollenizer plants were planted after triploid plants 4 and 10 in each plot. Row middles were 10 ft and in-row spacing was 2.5 ft.

Fertilizer and Pest Management

A total of 50 lb/ac N, 50 lb/ac P, 83 lb K, 33 lb/ac S, and 16.5 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 to fertigate the crop throughout the growing season. Liquid fertilizer with 4-0-8 analysis was initially applied through drip tape fertigation on 17 May 2022 and similarly on the following dates: 24 May 2022; 1, 6, 13, 21, 23, and 28 June 2022; 5, 11, and 21 July 2022. A total of 93 lb/ac N, 0 lb/ac P, and 186 lb/ac K were applied via fertigation throughout the growing season. Drip fertilizer application was calculated across the entire acreage being grown and not by bed covered with plastic mulch. Cumulative totals of applied fertilizer for the growing season were: 143 lb/ac N, 50 lb/ac P, 269 lb/ac K, 33 lb/ac S, and 16.5 lb Mg.

Fungicides were initially applied on 13 May 2022 and similarly on the following dates: 3, 10, and 22 June 2022; 1 and 19 July 2022. The following fungicides were applied and rotated to avoid potential development of resistance from diseases: Proline (5.7 fl oz/ac) was applied two times through the drip tube on 13 May 2022 and 6 June 2022; Copper (1 lb/ac), Quadris (15 fl oz/ac), Inspire (1 pt/ac), Manzate Pro Stick (3 lb/ac), Bravo (1 qt/ac), and Miravis Prime (11.4 fl oz/ac) were applied as foliar applications.

Insecticides were initially applied on 13 May 2022 and similarly on the following dates: 3, 10, 17, and 22 June 2022; 1 July 2022. Carbaryl (1 qt/ac) and Asana (8 fl oz/ac) were the primary insecticide products used, and were sprayed in rotation to avoid potential development of insecticide resistance. Admire Pro (10 fl oz/ac) was applied through the drip tube and a spray application, and Venom (6 oz/ac) was a spray application.

Miticide Banter (1 lb/ac) was applied on 3 June 2022. Applications of Gramaxone (1 qt/ac), Sandea (0.75 oz/ac), Clethodime Trizenta 2EC (8 fl oz/ac), and crop oil (1 qt/ac) were spot sprayed on weed escapes on 20 May and 30 June 2022.

Harvest and Yield Data Collection

Standard size triploid watermelon harvests took place on: 14 July (harvest 1), 20 or 21 July (harvest 2), 26 or 27 July (harvest 3), 4 or 5 August (harvest 4), 11 August (harvest 5), and 24 August (harvest 6). 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 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. For the category measures, whether by cwt, number, or bin boxes, the 9 – 13.4 lb category included fruits that ranged from 9 – 13.44 lb; the 13.5 – 14.4 category included fruits that ranged from 13.45 – 17.44 lb; the 17.5 – 21.4 lb category included fruits that ranged from 17.45 – 21.44 lb. Fruits that weighed more than 21.45 lb were included in the 21.5 or larger category.

Quality Evaluations

Evaluations of each melon entry included yield (fruit weight/ac, number/ac, bins/ac) across various size categories and a number of quality measures. 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 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 USDA standards. To measure hard seed population and seed trace size, fruits were cut longitudinally, and then the halves were cut laterally. The number of hard seeds and seed trace size on the cut surface were counted and recorded. Most of the quality measurements were taken in the early harvests (1-2). Additional internal evaluations included hollow heart incidence and severity, flesh color, and rind thickness. Length and width measures were taken on 5 fruit per plot to determine the length-diameter ratio which provides information as to whether the fruit is round, short-elongated, or long-elongated.

Results

Overall fruit yield and quality were very good for the duration of the study. Average precipitation rates over the growing season granted excellent growing conditions with minimal disease pressure, allowing for 6 harvests. Rots/decay was a minor issue throughout all harvests. Bird pecks on fruits in the initial two harvests occurred in a few plots, mainly in one replication. Those fruits that could not be weighed were counted and weights assigned to them based on average fruit weights in the plots for a given cultigen. A representative photograph of each cultigen entry is shown for the standard size cultigens (Figure 2).

Yield (cwt/ac)

The highest yielding standard size triploid cultigens for marketable fruit in the early harvests (1-2) were ‘Powerhouse’ (528 cwt/ac), ‘ACX6177’ (500 cwt/ac), and ‘Virtue’ (498 cwt/ac) (Table 1). The average marketable yield for the early harvests (1-2) was 405 cwt/ac.

In the mid-season harvests (3-4), the highest yielding standard size triploid cultigen was ‘El Capitan’ (364 cwt/ac), followed by ‘Talca’ (362 cwt/ac) and ‘Warrior’ (357 cwt/ac) (Table 2). The average marketable yield for mid-season harvests (3-4) was 252 cwt/ac.

In the late season harvests (5-6), the highest yielding standard size triploid cultigen was ‘XWT9161’ (468 cwt/ac), followed by ‘Rio Grande’ (411 cwt/ac) and ‘ACX6177’ (405 cwt/ac) (Table 3). The average marketable yield for late harvests (5-6) was 297 cwt/ac.

Cumulative marketable yield across all six standard size triploid harvests were greatest for ‘ACX6177’ (1151 cwt/ac), followed by ‘XWT9161’ (1086 cwt/ac) and ‘El Capitan’ (1084 cwt/ac) (Table 4). The average marketable yield across all harvests was 955 cwt/ac. These yields are substantially higher than what might be achieved in a normal production season.

The standard size triploid cultigens with the highest percentage early harvest based on cwt were ‘HMX633800’ (51%), ‘Golden Crisp’ (50%), and ‘Virtue’ (48%). Those cultivars with the highest percentage late harvest based on cwt were ‘XWT9161’ (44%), ‘Lajoya’ (41%), and ‘Rio Grande’ (40%) (Table 5).

Fruit size (weight)

The standard size triploid cultigens with the highest average fruit weight in the early harvests (1-2) were ‘Sierra Nevada’ (23.5 lb/fruit), ‘Virtue’ (20.5 lb/fruit), and ‘Essence’ (20.1 lb/fruit) (Table 6). The average fruit weight for the early harvests (1-2) was 17.3 lb/fruit. Fruits were generally larger (about 2-3 lb greater per fruit) than might typically be anticipated.

In the mid-season harvests (3-4), the standard size triploid cultigens with the highest average fruit weight were ‘Sierra Nevada’ (21.2 lb/fruit), ‘Essence’ (20.6 lb/fruit), and ‘El Capitan’ (20.2 lb/fruit) (Table 7). The average fruit weight for the mid-season harvests (3-4) was 17.9 lb/fruit.

In the late season harvests (5-6), the standard size triploid cultigens with the highest average fruit weight were ‘Sierra Nevada’ (17.2 lb/fruit), ‘XWT9161’ (14.6 lb/fruit), and ‘ACX6177’ (14.4 lb/fruit) (Table 8). The average fruit weight for the late harvests (5-6) was 13.1 lb/fruit. A reduction in average fruit size is expected in later harvests.

Average fruit weight across all six standard size triploid harvests was greatest for ‘Sierra Nevada’ (20.1 lb/fruit), ‘El Capitan’ (17.9 lb/fruit), ‘Virtue’ (17.5 lb/fruit), and ‘Essence’ (17.5 lb/fruit) (Table 9). The cultigens with the lowest average fruit weight across all harvests were ‘Tropical Sunshine’ (11.3 lb/fruit), ‘Lajoya’ (12.9 lb/fruit), and ‘Captivation’ (13.4 lb/fruit). The average fruit weight for all cultigens across all six harvests was 15.8 lb/fruit. It is worth noting that ‘Sierra Nevada’ consistently produced the largest fruit in all harvests.

Fruit number per plant

The standard size triploid cultigens with the highest fruit number per plant in the early harvests (1-2) were ‘ACX6177’ (1.9 fruit/plant) and ‘Embasy’ (1.7 fruit/plant) (Table 10). The average fruit number per plant averaged for all cultigens for the early harvests (1-2) was 1.4 fruit/plant.

In the mid-season harvests (3-4), the standard size triploid cultigens with the highest fruit number per plant were ‘Destination’, ‘El Capitan’, ‘Lajoya’, ‘Talca’, and ‘Warrior’ (1.1 fruit/plant for all) (Table 11). The average fruit number per plant averaged for all cultigens for the mid-season harvests (3-4) was 0.8 fruit/plant.

In the late harvests (5-6), the standard size triploid cultigens with the highest fruit number per plant were ‘Lajoya’ (2.3 fruit/plant), ‘Captivation’ (1.9 fruit/plant), and ‘XWT9196’ (1.9 fruit/plant) (Table 12). The average fruit number per plant averaged for all cultigens for the late harvests (5-6) was 1.5 fruit/plant.

Fruit number per plant across all standard size triploid harvests were the greatest for ‘Lajoya’ (5.0 fruit/plant), ‘ACX6177’ (4.4 fruit/plant), and ‘Captivation’ (4.3 fruit/plant) (Table 13). The average fruit number per plant across all cultigens and all harvests was 3.7 fruit/plant.

Marketable number per acre

The standard size triploid cultigen with the highest total marketable fruit number per acre were ‘Lajoya’ (7449 fruit/ac), ‘ACX6177’ (7231 fruit/ac), and ‘Embasy’ (6447 fruit/ac) (Table 13). The standard size triploid cultigens with the lowest total marketable fruit number per acre were ‘Golden Crisp’ (4138 fruit/ac), ‘HMC633800’ (4356 fruit/ac), and ‘Tropical Sunshine’ (4574 fruit/ac). Average marketable fruit per acre was 89% across all entries for the season. The main reason fruit were not marketable was because of small fruit size (<9.0 lb). The number of bins in the 60-count (9.0 – 13.5 lb), 45-count (13.6 – 17.5 lb), 36-count (17.5 – 21.4 lb), and 30-count (≥ 21.5 lb) categories are provided for harvests 1-2, 3-4, 5-6, and cumulatively for harvests 1-6, respectively (Tables 6, 7, 8, 9).

Quality

Interior fruit quality measurements included: soluble solids, flesh color, seed trace size, hard seed population, length and diameter, rind thickness, flesh firmness, and hollow heart rating. The standard size triploid cultigens with the highest Brix readings were ‘HMC633802 (Eleanor)’ (12.4), ‘HMC633800’ (12.0), and ‘Jet Ski’ (11.7) (Table 14). The cultigen with the lowest Brix reading was ‘Guardsman’ (10.3). The average Brix reading across all standard triploid cultigens was 11.0. The standard size triploid cultigens with the highest flesh firmness ratings were ‘Golden Crisp’ (4.6), ‘WDL9432’ (3.3), and ‘Destination’ (3.2). The standard size triploid cultigens with the lowest flesh firmness ratings were ‘Tropical Sunshine’ (2.1), ‘Valor’ (2.2), and ‘Warrior’ (2.2). The average flesh firmness rating across all standard size triploid cultigens was 2.6. There was a low incidence of hollow heart across all cultigens with 89.1% fruits with a HH0 rating (no crack in flesh). ‘Guardsman’ had the most severe incidence of hollow heart, with 25% of fruits with a HH3 rating (moderate cracking, unmarketable). ‘WDL9432’ had the most cases of hollow heart, with 35% of fruits with HH1 rating (hairline crack in flesh), 5% of fruits with a HH2 rating (obvious crack, but marketable), and 5% of fruits with a HH3 rating.

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. The results in this study are reflective of what generally occurred in the North Carolina commercial watermelon production acreage in 2022.

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. CucCap.