Mini triploid (seedless) watermelons (Citrullus lanatus) are a growing segment of the U.S. watermelon market due to their small, one-serving size. Although mini triploid watermelons were first released and commercially grown about 6 years ago, little information is available for optimum planting densities that are needed to achieve the greatest percentage of marketable fruit in the 3- to 8-lb range. In 2006 and 2007, the fruit grade distribution response to six plant densities (2489, 3111, 4149, 6223, 8297, and 12,446 plants/acre) of four mini watermelon cultivars (Betsy, Petite Treat, Valdoria, and Vanessa) was measured at the Southern Illinois University Horticulture Research Center in Carbondale. ‘SP-1’ was used as the in-row pollenizer at 25% of the total planting. Although all cultivars responded similarly to the plant densities evaluated, ‘Vanessa’ provided the greatest fruit number and weight per acre, and percentage of fruit in the mini grade, compared with the other cultivars. Marketable mini triploid watermelon yield dramatically increased with closer in-row spacings. At lower plant densities (wider in-row spacings), a greater proportion of icebox-sized fruit (>8 lb) was produced, and the amount of marketable, mini-sized fruit (3–8 lb) declined. The grade distribution of mini triploid watermelon numbers and weights were the greatest at the highest plant density evaluated [0.5 ft in-row spacing (12,446 plants/acre)], with about 80% of the total yield in the mini grade. The greatest net revenues were also obtained at this high density. This study indicated that it is critical for producers of mini triploid watermelons to recognize the dramatic impact that plant density has on marketable fruit yield (3–8 lb). Growers of mini triploid watermelons will see a drastic improvement in revenues with closer in-row spacings compared with the approximate 2 ft in-row spacings currently used (about 4000 plants/acre). The increased cost of higher plant densities are more than offset by the greater return on investment.
The inclusion of a smother crop used as a cash crop in an intercropping system may be an effective cultural control strategy for the management of weeds in organic production systems. In addition, a multilayered canopy created when intercropping species with different growth forms may limit germination cues for weed seeds and can allow for a more efficient utilization of resources that reduce competition to target crops from weeds. Watermelon (Citrullus lanatus) was evaluated for its ability to reduce weeds in a low-input organic system in Texas when planted alone or in various intercropping combinations that also included peanut (Arachis hypogaea), okra (Abelmoschus esculentus), cowpea (Vigna unguiculata), and hot pepper (Capsicum annuum). Watermelon significantly reduced total weed biomass when planted in monoculture and in all intercropping combinations compared with peanut, okra, cowpea, and pepper monocultures in year 1 of the 2-year study. Total weed biomass was reduced by 81%, 83%, 88%, and 92% in treatments containing watermelon on average as compared with pepper, peanut, okra, and cowpea grown in monoculture, respectively. Less effective weed suppression was obtained with watermelon in year 2. Pepper grown in monoculture had significantly higher weed biomass than all other treatments in year 2. Broadleaf weeds were effectively suppressed across all intercropping treatments in year 1, but nutsedges (Cyperus sp.) were consistently reduced both years, particularly when compared with monocrops with small leaf area such as pepper. The three and four species intercropping combinations consistently had high leaf area index (LAI) values, whereas pepper monoculture had significantly lower LAI values than all other treatments except for cowpea monoculture. There was a significant negative relationship between LAI and total weed biomass 33 d after last planting (r = −0.51, P < 0.01). There was a significant negative relationship between total weed biomass and total fruit yield in year 1 (r = −0.64, P < 0.01) but no significant relationship in year 2. Although findings were inconsistent in year 2 because of changes in precipitation amounts and in relative planting dates, these findings suggest that incorporating a multifunctional intercropping system that includes a low-growing vining crop such as watermelon or at least an architecturally complex mixture can optimize canopy density to reduce weed pressure from resilient perennial weeds such as nutsedge. This may offer organic producers another management tool for the control of perennial weeds.
Plasticulture has been successfully used to enhance growth and yield of horticultural crops, and also for season extension in cooler climates. The effect of three plastic mulches (silver on black, photoselective thermal green, and black) in combination with spunbonded polyester rowcover (0.9 oz/yard2) on spring-planted watermelon (Citrullus lanatus) production was investigated. Two red-fleshed cultivars [Sangria (seeded) and Crimson Jewel (triploid)] were used. Plastic mulches increased early and total marketable yield in comparison with bare ground for both cultivars, but net benefit increased in ‘Crimson Jewel’ only. In contrast, yield and net benefit were the same among plastic mulches. Rowcover increased soil and air temperature, with the effect being greatest at lower ambient temperatures. During a near-freeze event, air temperature under the rowcover was about 7.2 °F higher than without a rowcover. Rowcover increased early and total marketable yield, but fruit weight decreased in both cultivars. Yield distribution into three fruit size categories was inconsistent between the cultivars. In ‘Sangria’, the large fruit category had the highest yield proportion for all treatments. In contrast, the highest yield proportion of ‘Crimson Jewel’, with exception of mulch without rowcover, corresponded to small fruit. Rowcover increased gross income at wholesale prices, but net benefit was not different from without rowcover. Protection of high-value plants, such as triploid watermelon, against light freezes, however, may still justify the use of rowcover in early plantings.
Organic production is a fast-growing sector of agriculture in need of variety evaluations under their unique production systems. This study evaluated 16 watermelon (Citrullus lanatus) varieties for their performance characteristics under organic production practices. Plants were grown on plastic mulch-covered beds on land that had been certified organic in accordance with the U.S. Department of Agriculture National Organic Program. Six of the entries were F1 hybrids; the remaining entries were open-pollinated (OP) varieties. Of the 10 OP varieties, three were considered heirloom varieties, including Cream of Saskatchewan, Georgia Rattlesnake, and Moon & Stars. ‘Georgia Rattlesnake’ was the highest yielding variety and had the greatest average fruit weight. Along with ‘Georgia Rattlesnake’, ‘Nunhems 800’, ‘Nunhems 860’, ‘Orangeglo’, and ‘SSX 8585’ were included in the top five yielding varieties. The top five yielding varieties had fruit size that averaged more than 20 lb. Fruit size correlated with rind thickness, with lighter fruit having thinner rind (Pearson’s correlation, r = 0.779), which is not unexpected. ‘Sangria’ had the greatest average soluble solids content at 11.2%, which was greater than all entries with soluble solids less than 10%.
‘Sugarlee’ watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] is an early season cultivar that produces high-quality fruits suitable for shipping or local market sales. It is resistant to anthracnose, caused by race 1 of Colletotrichum lagenarium (Pass.) Ellis & Halsted, and fusarium wilt caused by Fu-sarium oxvsporum Schlect. f. sp. niveum (E.F. Sm.) Snyd. & Hans. Because it matures early, ‘Sugarlee’ fits well into Florida’s commercial production program and might be used in conjunction with ‘Dixielee’ to lengthen the shipping season for any given production area or grower. ‘Sugarlee’ has performed well in the Southern Cooperative Watermelon Trials during the period 1977-1981 and is well-adapted throughout most of the watermelon production areas in the eastern United States.
Field-grown muskmelons (Cucumis melo var. reticulatus Ser.) and watermelons [Citrullus lanatus (Thunb.) Matsum and Nakai] are sensitive to nutrient stress induced by low-pH soils. Severe foliar injury observed on melons grown in low-pH soils was caused by toxic levels of Mn and/or deficient levels of Mg in the leaf tissue. Manganese toxicity symptoms in muskmelons develop as chlorotic spotting on the adaxial surface of older leaves, with water-soaked rings around necrotic spots on the abaxial surface. In watermelons, Mn toxicity develops initially on older leaves as black-brown speckling on the abaxial leaf surface. Severe vein browning develops with age. Magnesium deficiency develops first on mature muskmelon and watermelon leaves as an interveinal bronzing, followed by a necrosis and browning of the interveinal tissue. Muskmelons are more sensitive to both Mn toxicity and Mg deficiency than are watermelons.
A study on the effect of ethephon, GA3, MH, and NAA on vegetative growth, flowering, and yield of bottle gourd [Lagenaria siceraria (Mol.) Standi.], round melon (Citrullus vulgaris ‘Fistulosus’), sponge gourd (Luffa cylindrica Roem.), summer squash (Cucurbita pepo L.), and watermelon (Citrullus lanatus Thunb. Matsum & Nakai) was conducted from 1979–1982. Maleic hydrazide applied at 150 mg/liter to bottle gourd and at 50 mg/liter to round melon, ethephon at 100 mg/liter to sponge gourd and at 250 mg/liter to summer squash, and GA3 at 25 mg/liter to watermelon were most effective in stimulating the elongation of main stem (except in summer squash), increasing branches per plant, lowering the male : female flower ratio, setting additional fruit, and producing highest fruit yield as compared to the untreated control. Chemical names used. (2-chloroethyl)phosphonic acid (ethephon); gibberellic acid (GA3); 1, 2-dihydro-3, 6-pyridazinedione (MH); 1-naphthaleneacetic acid (NAA).
The growth regulators abscisic acid (ABA), 6-benzylamino purine (BA), (2-chloroethyl)phosphonic acid (ethephon), aminoethoxyvinylglycine (AVG), and silver nitrate were applied in weekly or biweekly foliar sprays to watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] plants grown in a greenhouse. Both 10−3mBA and 10−4m ABA inhibited stem elongation, but had no effect on flowering patterns. Ethephon at 60 ppm and above prevented flower development, and at 15 and 30 ppm inhibited pistillate flowering and increased staminate/pistillate (S/P) flower ratios fivefold to sevenfold. Grafting watermelon scions to rootstocks of gynomonoecious and andromonoecious muskmelon did not affect sex expression or the response of watermelon to ethephon. AVG at 100 and 200 ppm and 500 ppm AgNO3 reduced the number of staminate flowers and promoted hermaphroditic flowering. In watermelon, contrary to other cucurbits, applied ethylene appears to suppress rather than promote ovary development during flower bud differentiation.
Intercropping of seedless watermelon [Citrullus lanatus (Thumb.) Matsum. & Nak.] and cotton [Gossypium hirsutum (L.)] in the eastern geographical area of South Carolina requires changes in normal crop-management programs but has the potential to improve grower profits compared with typical production of each crop separately. The alteration and timing of several normal crop-production practices for both crops can present challenges and must be well-defined for successful intercropping of watermelon and cotton in the region. Notable adjustments in production for watermelon are delayed planting date, reduced row spacing and bed width, and modification of herbicide applications. Significant changes in normal cotton production also include modification of herbicide applications, but additional considerations, such as temporal limits on side-dressed fertilizer and insecticide applications, are needed because of the raised beds and plasticulture used for watermelons and also because of labeling restrictions for pesticides across crops. Research was conducted to 1) identify modifications in standard crop-management procedures for watermelon and cotton intercropping; and 2) determine the feasibility and profitability of intercropping the crops. Although there was a slight numerical reduction in intercropped watermelon yield each year, there were no significant differences in total watermelon yield between intercropping and watermelon monoculture in any of the years. There were also no significant differences in watermelon fruit quality parameters (size, brix, hard seed, hollow heart) in any of the years. Intercropped cotton yield was significantly less than monoculture cotton yields in each of the three years. The net income from intercropping in each year was slightly less than the net income from watermelon monoculture.
Studies were conducted to investigate the influence of 50 μl·liter−1 ethylene on the cell wall, polygalacturonase (PG) activity, and electrolyte leakage of harvested watermelon [Citrullus lanatus (thunb) Matsum and Nakai] fruit. Electrolyte leakage was significantly increased in tissues from ethylene-treated fruit. The highest leakage occurred in distilled water, although the net effect of ethylene was less dramatic due to high leakage from control fruit. Leakage was greatly reduced but the ethylene effect more apparent compared to the control when tissues were incubated in an isotonic medium of mannitol or in isotonic medium containing CaCl2. Polygalacturonase activity increased markedly in ethylene-treated fruit, showing a > 10-fold rise during the first 6 days of treatment. Little change in PG activity occurred in melons stored in air, even in fruit stored for as long as 120 days. Cell walls of fruit exposed to ethylene exhibited acute ultrastructural damage. The decline in placental tissue firmness and the development of watersoaking symptoms observed by the third day of 50 μl·liter−1 ethylene treatment were apparently due, in part, to the PG-mediated cell wall breakdown resulting in cell rupture. Additionally, ethylene appeared to enhance membrane permeability.