Hort. Series #242

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; Andrew P. Pfefferkorn, 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 employee Kaleb Holder, as well as graduate student Kim Heagy for their assistance with this study. The cooperation and support of BASF/Nunhems, Hazera, Origene Seeds, Rijk Zwaan, Syngenta, and U.S. Agriseeds were also appreciated.

General Cultural Practices

This watermelon study was 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 mini 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 five 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). Although the acreage of mini watermelons grown in North Carolina is much less than the standard size watermelons, it is an important crop for some North Carolina growers, with one grower exclusively growing mini watermelon and no standard size watermelons.

Materials and Methods

Sowing and Field Preparations

Once all seeds were received from participating companies, they were planted into 72-cell poly trays to grow transplants (Hummert Int.; Earth City, MO). The mini watermelon cultigens were sown on 31 March 2022. The trays of sown seeds were placed in a germination room for 24-48 hours. Temperature in the germination room was kept between 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 4 weeks before transplanting, then “hardened” in a neighboring greenhouse for about 1 week before transplanting.

The study site was located at the Horticultural Crops Research Station in Clinton, NC. The mini watermelons were planted in block R5; a Norfolk soil type with a pH of 6.1, a phosphorus index of 99 and a potassium index of 118 (Figure 2). Telone II (12 gal/ac) was applied to the entire study area on 4 March 2022 for weed and nematode control. NPK fertilizer (10-10-10) at 500 lb/ac was applied pre-plant on 29 March 2022. 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

The mini triploid watermelon transplants were established in the field on 5 May 2022. Plot size for mini triploid watermelons was 1 row, 10 plants per row, 15 feet long with alleys of 10 feet between plots. Row middles were 10 feet and in-row spacing was 1.5 feet. Plots with missing plants were replaced 1 week after planting to achieve 100% plant stand. ‘SP-7’ and ‘Wingman’ (4 plants/plot) were used as the pollenizer plants in this study. ‘SP-7’ pollenizers were planted after triploid plants 1 and 7 while ‘Wingman’ pollenizers were planted after triploid plants 4 and 10 in each plot.

Fertilizer and Pest Management

A total of 50 units/ac N, 50 units/ac P, and 50 units/ac K 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 black 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, 15, 21, 23, and 28 June 2022; 5, 11, and 21 July 2022. A total of 89 units/ac N, 0 units/ac P, and 188 units/ac K was applied throughout the growing season. Drip fertilizer application was calculated across the entire acreage being grown and not by bed area covered with plastic mulch. Cumulative totals of applied fertilizer nutrients were: 139 units/ac N, 50 units/ac P, and 238 units/ac K.

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. Proline (5.7 fl oz/ac) was applied on 13 May 2022 through drip irrigation and was followed by Miravis Prime (11.4 fl oz/ac) applied as a spray on 19 July 2022 to prevent against potential fungal diseases like Fusarium wilt. The application of the following fungicides were rotated to avoid potential development of resistance from diseases: Copper (1 lb/ac), Quadris (15 fl oz), Inspire (1 pt/ac), Manzate Pro Stick (3 lb/ac), Bravo (1 qt/ac).

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) and Venom (6 oz/ac) were also applied once each.

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

Harvest and Yield Data Collection

Mini triploid watermelon harvests occurred on: 11 (harvest 1), 20 (harvest 2), 26 (harvest 3) July 2022 and 4 (harvest 4), 11 (harvest 5) August 2022. For the mini triploid watermelon study, fruits were placed in the following categories: < 3 lb, 3 – 7 lb, 7.1 – 9 lb, and ≥ 9.1 lb. Fruits were considered marketable if they weighed 3.0 – 9.0 lb. Fruit yields are reported as weight and number per acre.

Quality Evaluations

Evaluations of each melon entry included: 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 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 5 fruit per plot or 20 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 the 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 in the early harvests (1-2). Additional internal evaluations included hollow heart incidence and severity, flesh color, seed trace, and rind thickness.

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 5 harvests. Rots/decay was a minor issue throughout all harvests. Bird pecks on fruits were primarily on harvest 4 in a few plots, mainly in one replication. Those fruits that could not be weighed were counted and weights were 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 3).

Yield (lb/ac)

The highest yielding mini size triploid cultigens for marketable fruit in the early harvests (1- 2) were Excite (25606 lb/ac), 50036 (22840 lb/ac), and Bolita (22136 lb/ac) (Table 1). Some of the cultigens with high total fruit weight were Altata (38159 lb/ac) and Prestige (27871 lb/ac). They had more fruits that exceeded 9 lb and therefore were not considered marketable as a mini watermelon. The average marketable yield for the early harvests (1-2) was 20869 lb/ac.

In the mid-season harvests (3-4), the highest yielding marketable mini size triploid cultigen was Ocelot (21882 lb/ac), followed by Extazy (20829 lb/ac) and Petite Perfection (19653 lb/ac) (Table 2). The average marketable yield for mid-season harvests (3-4) was 18098 lb/ac.

In the late season harvest (5), the highest yielding marketable mini size triploid cultigen was Altata (24873 lb/ac), followed by Bolita (24851 lb/ac) and Extazy (24212 lb/ac) (Table 3). The average marketable yield for late harvest (5) was 21638 lb/ac. Average fruit size was about 1 lb smaller in the late versus the early (Table 1) and mid-season (Table 2) harvests.

Cumulative marketable yield across all 5 mini size triploid harvests were greatest for Extazy (67061 lb/ac), followed by Bolita (66088 lb/ac) and Petite Perfection (62784 lb/ac) (Table 4). The average marketable yield across all harvests was 60604 lb/ac. These yields are substantially higher than what might be achieved in a normal production season.

The mini size triploid cultigens with the highest percentage of fruit in the early harvests (1-2) by weight were Altata (36%), 50036 (35%), and Melania (34%). Those cultivars with the highest percentage of fruit in the mid-season harvests (3-4) by weight were Excite (38%), Ocelot (38%), and Extazy (35%). The cultivars with the highest percentage of fruit in the late season harvest (5) by weight were Sugar Rush (39%), Petite Perfection (38%), and Bolita (37%). Yield by weight were fairly equal across harvests regardless of cultigen.

Percentage of fruit distribution by weight over harvests

The percentage fruit weight across the various size categories is presented for harvests 1-2 (Table 6), harvests 3-4 (Table 7) and the late harvest (s) (Table 8). 80% of the fruit weight produced in the first 2 harvests were marketable fruit (3-9 lb) (Table 6); 68% of the fruit weight produced mid-season (harvests 3-4) were marketable fruit (Table 7); and 80% of the fruit weight produced in the late harvest(s) were marketable fruit (Table 8).

Fruit Size (weight)

The mini size triploid cultigens with the highest average marketable fruit weight in the early harvests (1- 2) were Melania (7.4 lb/fruit), Sugar Rush (6.8 lb/fruit), Bolita (6.5 lb/fruit) and Extazy (6.5 lb/fruit) (Table 1). The average fruit weight for the early harvests (1-2) was 6.3 lb/fruit.

In the mid-season harvests (3-4), the mini size triploid cultigens with the highest average fruit weight were Melania (6.9 lb/fruit) and Prestige (6.9 lb/fruit), Extazy’(6.7 lb/fruit), and 50036 (6.6 lb/fruit) (Table 2). The average fruit weight for the mid-season harvests (3-4) was 6.4 lb/fruit.

In the late season harvest (5), the mini size triploid cultigens with the highest average fruit weight were Melania (5.8 lb/fruit), Excite (5.6 lb/fruit) and Extazy (5.5 lb/fruit) (Table 3). The average fruit weight for the late harvest (5) was 5.2 lb/fruit. A reduction in average fruit size occurred in the later harvest.

Average fruit weight across all five mini size triploid harvests was greatest for ‘Melania’ (6.6 lb/fruit) (Table 4). The cultigens with the lowest average fruit weight across all harvests were      Petite Perfection (5.0 lb/fruit) and Ocelot (5.3 lb/fruit). The average fruit weight for all cultigens across all 5 harvests was 5.9 lb/fruit. ‘Melania’ consistently produced the largest fruit in all harvests.

Marketable number per acre

The cultivar Petite Perfection produced the greatest number of 3-7 lb size fruits in the early harvest (harvest 1-2) (Table 9). Other cultigens (500036, Excite) produced a similar number of total marketable fruit compared with Petite Perfection if the largest 7.1-9 lb size fruits were included.

For the mid-season harvest (3-4), marketable number of fruit exceeded 3000 fruit per are for cultigens 50036 (3049), Extazy (3122), Ocelot (3775), and Petite Perfection (3703) (Table 10). The average marketable fruit number produced per acre for mid-season harvest was 2904.

Marketable fruit number produced per acre was high for the late harvest (5) averaging 4153 fruits per acre (Table 11).

‘Petite Perfection’ had the highest fruit number produced per acre in the 3 to 9 lb size class (12415) for all five harvests when compared with all other cultigens (Table 12). Other cultigens that exceeded the marketable number of fruit produced per acre were Bolita, Extazy, Ocelot, and Sugar Rush.

Fruit number per plant

Fruit number per plant ranged from 1.5 to 1.7 fruits per plant for harvests 1-2 (Table 9.) The highest number of fruit per plant was produced by Altata (1.7) and the lowest number was produced by Ocelot (1.1)

Fruit number per plant were fairly similar across cultigens for harvests 3-4 and ranged from 1.1 to 1.5 fruits per plant (Table 10). A greater disparity in fruit number per plant was measured in harvest 5 (Table 11). ‘Melania’ produced only 1.2 fruits per plant while ‘Altata’ produced 2.2 fruits per plant.

The number of fruits per plant over all five harvests ranged from 3.8 (‘Melania’) to 5.0 (‘Altata’ and ‘Bolita’) (Table 12).

Percentage fruit distribution by number over harvests

The percentage marketable fruit number for early, mid-season, and late season harvests were 84%, 76%, and 80% for these harvests, respectively (Tables 13, 14, 15). Percentage marketable fruit number across all five harvests was 61% in the 3-7 lb category and 19% in the 7.1-9 lb category (Table 16). 80% of fruits produced across all cultigens were considered marketable based on fruit size.

Quality

Interior fruit quality measurements included: soluble solids, flesh color, seed trace size, hard seed population, length and diameter ratio, rind thickness, flesh firmness, and hollow heart rating. The mini size triploid cultigens with the highest Brix readings (soluble sugars) were Extazy (11.8), Petite Perfection (11.8), 50036 (11.6), Melania (11.6), Prestige (11.6) and Ocelot (11.5) (Table 17). The cultigen with the lowest Brix reading was Excite (10.3). The average Brix reading across all mini triploid cultigens was 11.3. The mini size triploid cultigens with the highest flesh firmness ratings were 50036 (3.9), Melania (3.4), Ocelot (3.4) and Petite Perfection (3.2). The mini size triploid cultigens with the lowest flesh firmness ratings were Altata (2.4), Prestige (2.7), and Bolita (2.8). The average flesh firmness rating across all mini size triploid cultigens was 3.1. There was a low incidence of hollow heart across all cultigens with 97% fruits with a HH0 rating (no crack in flesh). ‘Altata’ had the most severe & highest incidence rate of hollow heart, with 5% of fruits with a HH1 rating (hairline crack, is marketable) and 15% of fruits with a HH2 rating (obvious crack, still marketable).

Summary

Overall, yields and fruit quality in this study were excellent. Good growing conditions and minimal pest and disease 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.