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Watermelon Production In California

WATERMELON PRODUCTION IN
UC Vegetable Research
CALIFORNIA
& Information Center
AZIZ BAAMEUR, University of California Cooperative Extension Farm
Advisor, Santa Clara County; TIMOTHY K. HARTZ, University of California
Cooperative Extension Specialist, Department of Plant Sciences, University of
California, Davis; THOMAS TURINI, University of California Cooperative
vric.ucdavis.edu
Extension Farm Advisor, Fresno County; ERIC NATWICK, University of Cali-
fornia Cooperative Extension Farm Advisor, Imperial County; ETA TAKELE,
University of California Cooperative Extension Farm Advisor, Riverside County;
Vegetable
JOSE AGUIAR, University of California Cooperative Extension Farm Advisor,
Production Series
Riverside County; MARITA CANTWELL, University of California Coopera-
tive Extension Specialist, Department of Plant Sciences, University of California,
Davis; JAN MICKLER, University of California Cooperative Extension Farm
Advisor, Stanislaus County
PRODUCTION AREAS AND SEASONS
has striped skin and red flesh. Also grown is the
Watermelons (Citrullus lanatus) are produced in the
hybrid Royal Sweet, with striped skin and dark pink
northern Central Valley (Sacramento, San Joaquin, and
flesh. Sultan is an early-maturing, high-yielding
Stanislaus Counties); Central Valley (Kern and Tulare
hybrid. Icebox watermelon varieties grown in the
Counties); and southern California deserts (Imperial
northern San Joaquin Valley include Sugar Baby, Baby
and Riverside Counties). Statewide, watermelons are
Doll, and Tiger Baby.
planted from December to early July for harvest from
mid-May to late October. Yields reach 40 tons per acre
Seedless (Triploid) Varieties
(90 t/ha) under ideal conditions. Lower yields often
reflect depressed watermelon prices as much of the
Seedless varieties have in recent years accounted for
crop is left in the field.
the majority of the California watermelon acreage.
Commonly used seedless varieties include Fandango,
Super Cool, Nova, Laurel, Wonderland, Fire Cracker,
WATERMELON ACREAGE AND VALUE
Quality, Ultra Cool, Millionaire, AC 532, AC 5032, and
AC 5244. Additionally, miniature seedless watermel-
Average yield
Gross
on varieties, sometimes referred to as personalized
Year
Acres
(ton/acre)
value/acre ($)
watermelons, are now being commercially produced
2005
14,000
24.5
5,439
for grocery store sales. Popular miniature varieties
2006
14,900
25.5
5,763
include Precious Petite, Petite Perfection, Solitare, and
Extasy.
2007
13,400
25.5
5,763
Triploid varieties are transplanted because of low
Source: California Agricultural Statistics 2007 Crop Year-
seed vigor and high seed costs. Seed costs range from
October 2008, NASS Web site, http://www.nass.usda.gov/
$700 to $1,200 per pound ($1,540 to $2,640 per kg),
Statistics_by_State/California/Publications/California_Ag_
and each transplant costs from $0.28 to $0.35.
Statistics/index_casbultn.asp
In each production field, up to 30 percent of the
seedless watermelon planting is dedicated to seeded
VARIETIES
pollinator varieties such as Royal Sweet, Calsweet,
Seeded (Diploid) Varieties
Fandango, and Sangria. Fruit from the pollinators are
sold as a separate product. However, in large-scale
Sangria and Fiesta are popular All-Sweet hybrids
seedless watermelon production in low desert and
that are oblong and dark green with broken, light
San Joaquin Valley production areas, pollinators that
green stripes. The flesh is bright red with black seeds.
do not produce a marketable fruit (Supper Pollinizer--
Calsweet, the most popular open-pollinated variety,
SP-4, Patron, or Jenny) are used.
UNIVERSITY OF CALIFORNIA
Division of Agriculture and Natural Resources
http://anrcatalog.ucdavis.edu
Publication 7213
2 •
Watermelon Production in California
PLANTING
shapen fruit, and the occurrence of blossom end rot (a
physiological disorder in which the blossom end of a
Seeded Watermelon
fruit ceases to grow and becomes dark and leathery).
In large-scale production in desert areas of Southern
As harvest approaches care must be taken to avoid
California and in the San Joaquin Valley, few seeded
large fluctuations in soil moisture content, as heavy
varieties are currently grown. Watermelons are plant-
irrigation (or rainfall) can result in fruit splitting.
ed on flat beds 80 inches (2 m) wide and 8 to 12 inches
In the past, watermelon was usually irrigated by
(20 to 30 cm) high. In direct-seeded plantings, seed
the furrow method; irrigation was applied based on
is placed 0.5 to 0.75 inches (1.2 to 1.9 cm) deep. After
soil moisture status. In recent years, many growers
thinning and sidedressing, furrows are re-formed
have adopted drip irrigation. Drip irrigation lines
prior to furrow irrigation. For transplants, a single
are typically buried in the center of the soil beds. The
drip irrigation tape is laid 6 to 8 inches (15 to 20 cm)
irrigation system may be renovated each production
below the bed surface. Black plastic film, 72 inches
season or left in place for a number of years, depend-
(1.8 m) wide, is then laid flat on 80-inch (2-m) beds
ing on the grower’s management scheme and crop
to heat the soil and reduce weeds. Seeds or trans-
rotation. Drip irrigation scheduling is determined
plants are then planted directly through the plastic.
by potential evapotranspiration (ETo) estimates and
Transplants are set 24 to 36 inches (60 to 90 cm) apart.
crop growth stage; frequency of irrigation can vary
About 6 inches (15 cm) of the plastic is covered with
from once a week early in the season to daily during
soil at the edges to hold the mulch in place.
times of peak water demand. Some growers use drip
irrigation lines placed in every other furrow after crop
Seedless Watermelon
establishment. While this approach may not provide
Common seedless watermelon planting configura-
the full yield potential of a buried, in-row system, it
tions are one row of the seeded variety (pollinator)
does provide improved irrigation control compared
for every 2 to 3 rows of the seedless variety. However,
with furrow irrigation, and the system is portable,
other novel configurations are being used. The most
which eliminates management issues associated with
popular is the mixing of seedless and pollinator vari-
crop rotation. Regardless of irrigation technique, care
eties within the same row. In within-row plantings,
must be taken to minimize wetting of the bed tops.
the ratio of seedless to pollinator plants ranges from
Fruit in contact with moist soil may develop unsightly
2:1 to 5:1. As the seedless to pollinator ratio increases,
ground spots and fruit rots.
the number of beehives should be increased to ensure
pollination.
FERTILIZATION
Watermelon has moderate nutrient requirements com-
SOILS
pared with other vegetable crops, and due to its deep
rooting it is efficient in extracting nutrients from the
Watermelons grow best on nonsaline sandy loam or
soil. A high-yield watermelon crop will typically con-
silt loam soils. Light-textured fields warm up faster
tain less than 160 pounds per acre (180 kg/ha) of
in the spring and are therefore favored for early pro-
nitrogen (N) in its biomass, and, since most soils sup-
duction. Very sandy soils have limited water-holding
ply some nitrogen, the application of nitrogen beyond
capacity and must be carefully irrigated and fertilized
this amount is seldom warranted. Phosphorus (P)
to allow for high yield potential. Clay soils are gener-
fertilizer requirement is a function of soil test phos-
ally avoided for watermelon culture, but they can be
phorus level and soil temperature at the time of plant-
productive if irrigated with care to prevent prolonged
ing. Soils with greater 20 PPM bicarbonate extractable
saturation of the root zone (a condition that favors
phosphorus require little or no phosphorus fertiliza-
the development of root rot pathogens) and to allow
tion. Soils below that level may require as much as
good drainage between irrigations.
150 pounds per acre (168 kg/ha) of P2O5, with phos-
phorus requirement increasing in colder soil and with
IRRIGATION
lower soil test value. Soils with more than 120 PPM
Although watermelon is a deep-rooted crop able that
exchangeable potassium (K) can support high-yield
can tolerate a significant degree of soil moisture stress,
watermelon production without fertilization, although
peak production requires timely irrigation. After crop
a maintenance application of up to 150 pounds per
establishment (either by seed or transplant), irriga-
acre (168 kg/ha) of K2O can be used to maintain long-
tion may be witheld for a period of several weeks to
term soil fertility. Soils below 120 PPM exchangeable
encourage deep rooting. However, irrigation should
potassium should be fertilized with up to 150 pounds
be managed to minimize water stress throughout the
per acre of K2O to ensure peak production.
fruit set and fruit sizing periods. Water stress dur-
P should be applied preplant. Potassium applica-
ing early fruit development can result in small, mis-
tion can be made preplant, after planting, as a sid-
3 •
Watermelon Production in California
edress application, or delivered in irrigation water
ballus) are soilborne diseases most often observed
(fertigation). Nitrogen application is typically split
when temperatures are high and plants are stressed.
between a small preplant and one or more in-season
Both diseases commonly occur in the desert, and
applications. In drip-irrigated culture, small weekly
they occasionally cause damage in the southern San
nitrogen fertigations may be used to time nitrogen
Joaquin Valley. Death of crown leaves combined with
delivery to crop uptake rate.
gray stem lesions are symptoms associated with char-
POLLINATION
coal rot. Monosporascus vine decline may cause com-
plete canopy collapse when fruit are 2 to 3 weeks from
One to two bee colonies per acre should be placed in
harvest. Structures diagnostic for M. cannonballus can
the field when male flowers begin to appear. Poor pol-
be seen as small, black, round structures protruding
lination often causes misshapen fruit. A watermelon
from dead root tissue of affected plants.
plant seldom produces more than 2 to 3 harvestable
In the northern San Joaquin Valley, Verticillium wilt
fruit. While it is too expensive to remove all excess
(Verticillium dahlia and V. alboatrum) may be a problem.
fruit, misshapen and split fruit may be culled in the
Verticillium wilt causes yellowing of the foliage and
field to allow the plants to channel nutrients into mar-
wilting. In severe cases whole plants may die.
ketable fruit. Care must be taken to prevent the bee
Fusarium wilt (Fusarium oxysporum f. sp. neveum)
colonies from being exposed to pesticides.
Race 1 is present in many California soils. It typi-
cally affects runners on one side of the plant, but in
INTEGRATED PEST MANAGEMENT
advanced stages it may cause the entire plant to wilt.
For detailed information about integrated pest man-
Watermelon varieties with resistance to Fusarium
agement for watermelons, see the UC IPM Pest
Race 1 are available but may be ineffective in soils
Management Guidelines for Cucurbits Web site,
with a high Fusarium Race 1 population. The reduc-
http://www.ipm.ucdavis.edu/PMG/selectnewpest.
tion in canopy coverage that occurs in response to
cucurbits.html, or consult your local UCCE Farm
infection by soilborne pathogens exposes fruit to sun-
Advisor. Herbicides, insecticides, and fungicides
burn.
should always be used in compliance with label
Cucumber mosaic virus (CMV), Papaya ringspot
instructions.
virus (PRSV-W), Watermelon mosaic virus (WMV), and
Zucchini yellow mosaic virus (ZYMV) are aphid-trans-
Insect Identification and Control
mitted viruses that cause leaf distortions and mosaics.
Whiteflies, cutworms, beet armywoms, aphids, spider
Yield losses are most associated with mixed infections
mites, darkling ground beetles, leafhoppers, cabbage
(2 or more viruses) and virus transmission at early
loopers, and leafminers are the most serious insect
stages of crop development.
pests of watermelon. Rind scarring from worm dam-
Cucurbit yellow stunting disorder virus (CYSDV)
age is a serious defect that reduces market value.
is a whitefly-transmitted virus recently detected in
The silverleaf whitefly, Bemisia tabaci Biotype B (also
Arizona and in the Imperial Valley, California. This
known as B. argentifolii) causes direct feeding damage
virus causes severe yellowing of the leaves and is
to watermelon and fruit contamination via honey-
moved in symptomless watermelon transplants.
dew deposits that support growth of sooty molds.
Sudden wilt is characterized by premature plant
Silverleaf whitefly is also a vector of two viruses
death that commonly occurs after fruit set. The pre-
diseases (Cucurbit yellow stunting disorder and
cise cause is not well determined, but a complex of
Cucurbit leaf crumple) that affect watermelon yield
environmental conditions and pathogens including
and quality.
Fusarium spp., Rhizoctonia spp., and Pythium spp. may
be implicated. Extreme waterlogging or drought con-
Disease Identification and Management
ditions that reduce plant resistance can contribute to
Powdery mildew (Podosphaera xanthii) can rapidly
watermelon sudden wilt.
cover leaves, causing reduced crop growth and pre-
mature defoliation. Subsequently, losses in fruit yield
Physiological Disorders
and quality (due to sunburn) may occur. Repeated
Physiological disorders are caused by nonpathogenic
fungicide applications are often necessary to avoid
agents that affect fruit quality. Usually, aesthetic qual-
economic damage due to powdery mildew. Selection
ity is degraded. The cause can be either one or a
and rotation of effective fungicides is critical for con-
combination of environmental, genetic, or nutritional
trolling powdery mildew epidemics, especially in
factors.
growing areas where fungicide resistance in the P.
Blossom-end rot (BER) is caused by uneven irriga-
xanthii population has been reported.
tion that leads to calcium (Ca) restriction. BER can be
Charcoal rot (Macrophomina phaseolina) and
avoided by even irrigation and proper nitrogen and
Monosporascus vine decline (Monosporascus cannon-
calcium management.
4 •
Watermelon Production in California
Misshapen or pear-shaped fruit can be caused by
to 11.8 kg), and number 2, 8 to 14 pounds (3.6 to 6.4
poor pollination that leads to restricted growth at the
kg). Inferior melons may be sold at nearby markets;
stem end due to of the absence of developing seeds.
culls (discolored, misshapen, sugar-cracked, blossom-
Poor pollination can be minimized by increasing the
end rotten, and insect-damaged fruit) are discarded.
number of beehives in the field. Cold temperatures
Containers that hold 60 to 80 melons and weigh 1,100
can also cause misshapen fruit.
to 1,200 pounds (500 to 545 kg) are shipped on flatbed
Hollow heart is marked by cracks in the heart of
trucks to terminal markets or wholesale receivers. The
the watermelon fruit due to accelerated growth in
containers are covered to prevent sunburn in transit.
response to ideal growing conditions facilitated by
Seedless melons are sorted according to size and
ample water and warm temperatures.
packed in cartons containing 3, 4, 5, 6, or 8 fruit.
Cross stitches are elongated necrotic wounds (0.5
“Fours” and “fives” are preferred sizes; “sixes” and
to 1.0 inch long) that are perpendicular to fruit length.
“eights” are common later in the season after the
The cause of cross stitches is unknown.
crown-set melons have been removed from the vine.
Sun scald (burn) results from exposure to intense
The rough gross weight of a carton is 40 to 50 pounds
solar radiation that leads to dehydration and over-
(18 to 22.7 kg). Seedless melons may also be sold in
heating damage of the rind tissue. Sun scald can be
large bulk containers.
alleviated by covering the fruit with vines or straw
Personal seedless watermelons are sorted by size
material.
and packed in single-layer boxes containing 6, 8, 9, or
11 fruit. Shipping boxes roughly weigh 34 pounds (15
Weed Management
kg) and arranged 50 boxes per pallet
Most growers use only mechanical cultivation
and hand-hoeing for weed control in the low des-
POSTHARVEST HANDLING
ert growing regions. However, herbicides are used
Watermelons may lose crispness and color in pro-
in the northern San Joaquin Valley. Herbicides are
longed storage. They should be held at 50° to 60°F
applied with shallow incorporation, and transplants
(10° to 15°C) and 90 percent relative humidity. Sugar
are placed with the roots below the treated zone.
content does not change after harvest, but flavor may
Postemergence herbicides are used to control grasses.
be improved due to loss in acidity of slightly imma-
Methyl bromide was commonly used in the past in
ture melons. Chilling injury will occur after several
field fumigations, but now metam sodium is used for
days below 41°F (5°C). The resulting pits in the rind
preplant weed suppression.
will be invaded by decay-causing organisms.
HARVEST AND HANDLING
MARKETING
Watermelons do not slip from the vine or emit an
California produces approximately 330,000 tons (302
odor when ripening, unlike muskmelons. Indicators
T) of watermelon per year (1.95 million for the United
for picking watermelons include color change (the
States, average of 2004–2006), grossing an average of
most reliable), blossom end conditions, rind rough-
$72 million per year ($367.3 for the United States) for
ness, and drying of the nearest tendril to the fruit (less
the same period. Limited supplies of California water-
reliable). A sharp knife should be used to cut melons
melons are available beginning in May. Production
from the vines; melons pulled from the vine may
peaks in August, and the season ends in November.
crack open. Harvested fruit are windrowed to nearby
Most California watermelons are marketed in the west-
roadways, often located 10 beds apart. A pitching
ern United States and Canada. Major competition in
crew follows the cutters and pitches the melons from
the market comes from Mexico, Arizona, and Texas.
hand to hand, then loads them in trucks to be trans-
ported to a shed. Melons should never be stacked on
the blossom end, as excessive breakage may occur.
COST OF PRODUCTION
Loss of foliage covering the melons can increase
Costs of production of watermelon would vary
sunburn. Exposed melons should be covered with
depending on location. Costs such as water and land
vines, straw, or excelsior as they start to mature to
lease vary by the production area, and the amounts
prevent sunburn. Each time the field is harvested, the
of inputs such as fertilizer, pesticide, etc. depend
exposed melons must be re-covered. Most fields are
on weather and soil. Generally, watermelon pro-
picked at least twice. Some fields may be harvested a
duction is labor intensive, especially in harvesting
third or fourth time, depending upon field condition
and postharvest handling. For more information,
and market prices.
see Sample Cost to Establish and Produce Watermelon,
Seeded melons are sorted and packed in large, stur-
Imperial County, 2004, at the UC Davis Agriculture
dy, tri-wall fiberboard containers. The melons are sort-
and Resource Economics Web site, http://ucce.ucda-
ed according to grade: number 1, 14 to 26 pounds (6.4
vis.edu/files/filelibrary/5600/42709.pdf.
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