Crop Production Guidelines |
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By: Hector Valenzuela, Randall T. Hamasaki, and Steve Fukuda
University of Hawaii Cooperative Extension Service Assistant
Vegetable Specialist, Associate County Extension Agent, and
County Extension Agent, respectively.
INTRODUCTION
Cucumber (Cucumis sativus) a member of the Cucurbitaceae family,
is native of Asia and Africa, where it has been consumed for
3,000 years. It is a popular fresh market vegetable in salads and
also is processed into kim chee and oriental-type pickles in
Hawaii. Over 60% of local production is in Mountain View and Kona
on the island of Hawaii, Kauai and Oahu. The crop is susceptible
to serious losses from such pests as the silver leaf (or
sweetpotato) whitefly, the melon fly, leafminers, mosaic viruses,
and to soil-borne and foliar diseases. Production volumes are
40-50% lower during the winter months when diseases are more
prevalent. The pickling-type cucumbers, grown for processing in
the continental U.S., are not grown to a large extent in Hawaii.
Crop Growth and Sex Expression
Cucumber is an annual deep-rooted (ca. 3 ft) crop with tendrils
and hairy leaves. The plants may have an indeterminate,
determinate, or a compact plant habit. The compact growth habit
consists of plants with shorter internode length than plants with
indeterminate or determinate growth habit. Optimum growth occurs
between 70-75F (20-25C), with growth reduction occurring below
60F (16C) and above 90F (30C).
Several flowering habits exist in cucumbers. Most cultivars are
monoecious, with separate male and female flowers in the same
plant. Gynoecious or "all-female" cultivars produce
only female flowers resulting in up to 13 times more female
flowers than those obtained in monoecious cultivars. The
so-called "PF" hybrids produce predominantly female
flowers but also produce a small number of male flowers. Often
"pollination" plants are supplied to insure
fertilization on "PF" types. Many cultivars grown in
greenhouses such as European cucumbers are parthenocarpic.
Parthenocarpic varieties require no pollination for fruit
production. In fact, pollination of these cultivars causes an
off-shaped appearance of the fruit.
The first flowers of monoecious plants are staminate or 'male'
followed by pistillate or 'female' flowers from which fruits are
born. Sex expression in cucumber may be affected by several
factors such as plant density, plant stress, temperature, and
light intensity. Reduced rates of female flowers in gynoecious
cultivars may result from exposure to stress caused by high plant
population densities, insect attack, wind damage, and
combinations of low light intensity and high ambient
temperatures. The commercially available hormone etephon, at
125-250 ppm, increases the production of pistillate or female
flowers in gynoecious cultivars. Cucumbers will interbreed with
other cucumber cultivars but not with melons nor squash. Some
markets, such as the Japanese market, prefer 'bloomless' fruits,
or fruit free of the natural film or powdery tissue that cover
the skin of cucumbers and several other vegetables.
Cultivars
Cultivar selection is one of the most important decisions made
during the crop production process. Selection of cultivars
adapted to local growing conditions and seed quality are
significant production factors that deserve careful planning and
consideration. Desirable traits required for local cultivars
include high productivity, high fruit crispness and firmness, and
resistance to watermelon mosaic virus, zucchini mosaic virus,
cucumber mosaic virus, powdery mildew, and angular leaf spot
(Figure 1). As a standard for fruit quality the market still
relies on the old 'Burpee Hybrid' first released in 1945 and
which included >75% of cucumbers grown locally in the 1960s.
Newer commercial cultivars are available with resistance to
important diseases such as angular leaf spot, anthracnose,
cucumber mosaic virus, watermelon mosaic virus, zucchini yellows
mosaic, downy mildew, powdery mildew, and scab. As described in
the previous section, hybrid cucumber cultivars may be
monoecious, gynoecious, or parthenocarpic. Parthenocarpic
cultivars will produce seedless fruit in the absence of bees and
pollination during the crop growth cycle. If bees are present for
pollination, parthenocarpic plants will yield normal seeded
fruits but fruit may be off-shaped. Cultivars adapted to Hawaii
include:
Table 1. Cultivars adapted to Hawaii
Western Slicing Types Fruit Length Fruit Diameter
(inches) (inches)
Burpee Hybrid II 8 2-1/2
New Market #2 10 2-1/2
Sweet Slice Hybrid 1 1 2-1/2
Lani Hybrid (UH cultivar) 9 2-1/2
Milo Hybrid* 8 2-1/2
Dasher II (gynoecious) 8 2-1/2
Sakata #69 8 2-1/2
Slicemaster 8 2-1/2
Slicing Oriental types (monoecious with an upright habit):
Progress Hybrid-- 10 2
Tasty Gem Hybrid-- 10 2
Spring Swallow 7 1
* (UH cultivar, indeterminate monoecious)
Promising cultivars in Hawaii based on trials in Oahu include
Genuine and Spring Swallow. Other for-trial cultivars include
Soarer, Southern Delight, Pegasus, Green Knight, Tokyo Slicer,
Conquistador, and Brocade.
FERTILIZER RECOMMENDATIONS
Soil Type
Cucumbers are adapted to a wide variety of soil types which have
good drainage and adequate soil-holding capacity.
Optimum pH
Cucumbers don't perform well on acid soils but do well under
slight acidity. The optimum pH is 5.5-7.0. In general, if the
soil pH is below 5.8 and the available soil calcium is less than
2,000 lbs. per acre, apply 2,000 lbs. per acre (4.5 lbs./100
square feet) of agricultural lime 8 to 12 weeks before planting.
However, some Hawaiian soils may require considerably more lime.
Liming to a pH of 7.2 to 7.5 plus the use of nitrate-nitrogen
fertilizer sources help to reduce incidence of Fusarium wilt,
Fusarium oxysporum in the field. Micronutrient availability may
be reduced at a pH above 6.5.
Nutrient Rates and Placement
Fertilizer applications should be based on crop nutrient demands
and stage of crop growth. Tissue and soil analysis help to
determine how much fertilizer to apply to complement the nutrient
levels already available in the soil. Soil samples should be
taken and appropriate fertilizers added as recommended by
University of Hawaii soil scientists for the particular soil
type. If the soil series is not known, growers should supply
ample information about the origin of the soil sample so that the
soil series can be determined through soil survey maps. Excessive
fertilizer rates beyond crop needs may result in salt buildup,
phytotoxic effects on plant growth, ground water contamination,
delayed harvest due to excessive foliage growth, and capital
losses due to purchase of unneeded fertilizer. Cucumbers
tolerance to salt build-up in the soil ranges from moderate to
sensitive.
Estimated rates of nutrient removal for N-P2O5-K2O-MgO-CaO in
fruits, leaves and stems with yields of 10,000 lbs/Acre are
32-9-44-6-23 lbs/Acre, respectively. Over 80% of the total crop
nutrient removal takes place during the fruiting stage of crop
growth.
Greenhouse studies of fruit growth and nutrient uptake rates in
the continental U.S. indicate that cucumbers respond better to
nitrate than ammonium N fertilizer sources. This results in
greater Ca, Mg, and K levels in the fruit. Recommended fertilizer
rates for Hawaii are 1,500 to 2,000 lbs. per acre of 15-15-15 or
similar N-P-K fertilizer. Band half of the fertilizer 3 inches to
the side and 3 inches below the seed at planting. Side-dress one
quarter of the fertilizer rate at 3-4 weeks after planting and
the remaining quarter, 6 - 7 weeks later. With the onset of
harvest, side-dress every two weeks with a 3:1 mixture of sulfate
of ammonia (21% Nitrogen): muriate of potash (61% potassium) or a
1:1 mixture of urea (46% nitrogen): muriate of potash at a rate
of 200 lb per acre. Since N and K tend to leach, apply additional
fertilizer after a heavy rain.
On soils very low in available phosphate, apply 1,500 lb/Acre of
treble super phosphate (47% phosphorus) or 1,500 lb/Acre of
monoammonium phosphate (11-52-0). If both lime and phosphates are
required, both should be incorporated together 8 - 12 weeks
before planting.
Potassium improves fruit deep green color, firm flesh, shape, and
overall yields.
Magnesium is required in cucumbers to help obtain a deep-green
fruit color. Magnesium deficiencies will be intensified in fields
which have received high N or K fertilizer rates. For soils low
in magnesium, apply magnesium sulfate (epsom salt, 9.8% Mg.) or
its equivalent at 150 - 500 lbs/Acre. Soil magnesium deficiencies
can also be corrected with periodic light dolomitic limestone
applications.
Cucumber's nutrition program should be tuned to achieve maximum
yields and optimum market quality. For example insufficient
potassium will result in misshapen fruit or
"bottlenecks", and low nitrogen restricts growth,
modifies the length-to-diameter ratio of fruit, reduces fruit set
and color development. The symptoms listed in Table 2 should be
helpful to help diagnose specific deficiencies. However, be aware
that abnormalities such as those caused by root rot and nematode
infections may produce similar symptoms in plants.
Table 2. Common Nutrient Deficiency Symptoms in Cucumber
Nutrient Deficiency Symptoms
Nitrogen Mature leaves yellowish green to yellow;
stems slender, hard and fibrous; fruits light in
color, pointed at blossom end; Stunted roots
turn a brownish color and then die.
Phosphorus Mature leaves change from a dark to dull
green; Stems slender; Fruits dull green to
bronze.
Potassium Mature leaves bluish green near veins,
Bronzing and necrosis of leaf margins; Young
leaves are puckered or crinkled; Fruits
constricted at stem end; Plant growth slow.
Magnesium Plants are small and appear weak;
center-veinal chlorosis on mature leaves,
veins remain green; Mature leaf edges brittle
and ragged; Yields are low and quality of fruit
is poor.
Calcium Misshapen fruit; Water soaked and necrotic
lesions on blossom end; "Pillowy" fruit
disorder. Reduced shoot, root and fruit
growth.
Organic amendments
Manure applications improve quality and yields of vine crops.
Composted manures help to improve soil texture and drainage, and
act as slow-release fertilizers. Apply up to 20,000 lbs/Acre (10
MT/Acre) as a complement to calibrated chemical fertilizer
applications. Often, chicken manure is added at amounts of up to
1 lb/hill and it is worked into the soil.
Fertigation
Available soluble fertilizers may be injected through the
irrigation system in place of sulfate of ammonia and muriate of
potash. N levels of 200 ppm and K levels at 250 ppm in
fertigation solution are recommended for maximum cucumber yields.
A schedule for fertilizer rate applications in cucumber is listed
in Table 3. Before using chemicals through irrigation systems, be
aware of any regulations which may apply.
Table 3. Timing and Fertilizer Injection Rates Recommended for
Cucumbers, beginning at Transplanting
Timing Fertilizer Rates
(Weeks after transplanting) (lbs/Acre/week)
1st to 3rd week 2.5 lbs of 20-10-20
4th to 8th week 5 lbs of 20-20-20
9th to 16th week 6.25 lbs of 20-20-20
Epson salt 5 lbs at 4th, 8th, 12th week
Nutrient Tissue Analysis
Periodic nutrient analysis of foliage tissue is useful to obtain
an estimate of a crop's nutritional status and serve as a record
of crop performance. The tissue analysis should be calibrated
with soil fertility levels, according to soil samples taken
before planting. For tissue analysis, collect a young mature
whole leaf (petiole and leaves) located below the last open
flower cluster. A representative tissue sample from a field plot
will consist of 25 to 50 collected leaves free of insects or
disease. Collect samples prior to the fruiting stage. Recommended
optimum ranges for cucumbers are found in Table 4.
Table 4. Recommended Tissue Nutrient Ranges for Cucumber
Nutrient Target Level (1)
N 3.3-4.0%
P 0.4-0.8%
K 2.8-4.0%
Ca 1.8-2.5%
Mg 0.4-0.5%
S 0.3%
Fe 108 ppm
Zn 23 ppm
Mn 60 ppm
Cu 8 ppm
B 25 ppm
(1) Percent dry matter content. Nutrient level of young mature
leaf at the pre-fruiting stage (5th-6th leaf from apex).
CULTURE AND MANAGEMENT PRACTICES
In typical commercial operations, cucumbers are grown in
polyethylene-mulched beds with drip irrigation. Water and
nutrients inputs are closely monitored and adjusted with drip
irrigation. The plastic mulch helps control weeds, improves
efficient use of water and fertilizer, and reduces incidence of
fruit rots. Yields of ground culture are 40-80% of those obtained
with mulch culture. Cucumbers are susceptible to damage from wind
and need the protection provided by windbreaks in wind-prone
areas. Examples of commonly used windbreaks include 'Tropical
Coral' Tall Erythrina (Erythrina variegata L.), and wild cane
(Saccharum spontaneum moentai). Other suitable windbreaks may
also be used. Where annual windbreaks are used, an in-field
rotation may be conducted for the following crop by rototilling
the row where the windbreak was grown, planting in the row, and
preparing the bed in that area.
Time to Plant
In Hawaii, cucumbers are planted year round from sea level to
3,000 feet (0-1000 m) elevation, and from April to October at
elevations above 3,000 ft (1000 m). Often cucumbers at high
elevations become bitter in the winter season.
Field Preparation
The field may require plowing or subsoiling to break a hard pan.
The field is then disked and/or tilled to break up soil clods.
Soils with poor drainage benefit from manure or other organic
matter materials incorporated into the soil. If a soil amendment
such as lime is needed, broadcast it before plowing and
incorporate at a depth of 10-12 inches 8-12 weeks prior to
planting. This allows the lime to react with the soil to correct
pH assuming sufficient moisture is available in the soil. If a
nematicide is used, apply at least two weeks prior to planting in
light soils and three weeks prior to planting in heavy soils.
Cover crops should be turned over 2-4 weeks (earlier for the ones
that decompose faster) prior to planting cucumbers to allow for
litter decomposition.
Propagation
Cucumbers are both direct seeded and transplanted in Hawaii.
Proper soil temperatures for seed germination range between
55-95F (13-35C). Thinning is conducted in two operations for
direct seeded crops . The first thinning occurs at the two leaf
stage leaving 4-5 plants per hill. The final thinning takes place
about a month after seeding, leaving two plants per hill.
Cucumbers can be transplanted when adverse growing conditions are
expected during the initial growing stages, when expensive seed
is used, or for special operations as in hydroponic cultures.
About 1-2 lbs/Acre of seed is required for direct-seeded
cucumbers (there are about 1100 seed per ounze). Cucumber
inoculation with Vesicular-Arbuscular Mycorrhiza fungi Glomus
spp., which has been shown to improve nutrient uptake in other
crops, also improved tolerance to salt stress and prevented
attack from damping-off, Pythium ultimum, in cucumbers. However,
Glomulus seed inoculants are not currently commercially
available. Seed at a depth of 3/4-1 inch.
Spacing
Many variations of plant spacing are used. The rows are spaced
4-6 feet to allow space for spraying and harvesting in trellised
fields. Plant spacing within the row is 1-5 feet, depending on
the number of plants per hill, and on vine vigor of the
particular cultivar. Cultivars with vigorous lateral growth such
as Burpee Hybrid II should have an increased spacing. Cucumbers
grown in plastic mulch may be planted two rows to a bed with rows
in the bed spaced 9 inches. Greenhouse and hydroponic grown
cucumbers are generally planted closer, and may require pruning.
Training
Cucumbers may be grown in trellises or in ground culture. Trellis
the oriental slicing types to prevent the development of crooked
fruits. Yields of Fancy and No. 1 fruits for non-trellised
cucumbers will be 40-75% of those obtained with staked cucumbers.
The major advantages and disadvantages of trellising a cucumber
crop are listed in Table 5.
Table 5. Advantages and Disadvantages of Trellised-Cucumbers
Advantages
a. Increased harvesting efficiency and greater yields
b. Improved pest management
c. Straighter fruits
d. Uniform fruit color
e. Reduction of fruit loss to soil diseases
f. More plants per acre due to closer rows.
Disadvantages
a. Extra cost of trellising materials
b. Extra-labor costs to erect, dismantle and train vines
c. Plants are more prone to wind damage
Trellises constructed along the row are 5-7 ft high. Space posts
at a maximum of 15 feet. An eight gauge wires is placed on top
and a 12-gauge wire on the bottom. Twine or plastic netting is
used for the trellis. Three to four trips through the field are
required to train the vines into the trellis until the vine
reaches over the top wire. The potential also exists to double
crop cucumbers following a staked tomato crop, thus saving the
cost of staking and mulching. In addition, double cropping will
result in improved fertilizer use efficiency in the field.
Pollination
Monoecious cucumbers are dependent upon honeybees for
pollination. Eight to 10 bee visits per flower are required for
adequate fruit formation in cucumbers. In many states this is
obtained with 1-3 beehives (20-30,000 bees per hive) per
production acre. Trials in California showed that placing 3 hives
instead of 1 beehive/Acre resulted in an increase of 100
crates/Acre of marketable fruit, earlier harvest, and reduced
harvest period resulting in 33% less harvests. Professional
bee-keepers provide bee hives in some states but these services
are not currently available in Hawaii.
Pesticide applications should be managed carefully since most
organic pesticides are toxic to bees. To minimize bee kills a)
Know the location of the bee hives around the field; b) Avoid
spraying when bee activity is high; c) Read the pesticide label
to determine its toxicity to bees; d) Avoid spraying near bee
hives; and e) Avoid leaving puddles around the pesticide rig
which might attract and poison thirsty bees.
Poorly developed or misshapen fruit may be the result of stress
during the embryo-forming period of fruit growth. Any unevenness
in seed formation will produce misshapen fruit. A "wasp
shape", for example, may be the result of late pollination
(1 or 2 days after full bloom or anthesis), causing only the
ovules at the stigma end of the fruit to produce seed. Also,
fertilization of the flowers may be interrupted due to internal
physiological factors such as a nutrient deficiency. Evidence
indicates that Boron applications at rates of 0.6 lbs/Acre may
improve pollination efficiency in boron-deficient fields.
Irrigation
Cucumber requires a constant water supply to reach hiqh quality
and yields. Periods of growth when the plant is most susceptible
to irrigation deficits include seed germination, flowering, and
fruit enlargement. The frequency of irrigation is largely
dependent on soil type and weather conditions. In general, for
sandy soils with dry weather, the fields should be irrigated at
least every other day if not more often at a rate of 1-2 inches
per week. Cucumber in Hawaii is normally drip irrigated. Two or
three weeks after planting, a second drip line is installed about
18 inches parallel from the one applied at planting. Thus, there
is a drip line on both sides of the row. In sprinkle-irrigated
fields, avoid irrigation between 8-11 AM to prevent interference
with honeybees.
PESTS
Cucumber yields are frequently reduced by a myriad insect,
disease, and weed pests. For example over 40 different diseases
are known to infest this crop. Cucumbers are especially
susceptible to pest attack when growing conditions are less than
ideal and when sound cultural practices have not been followed.
Integrated Pest Management (IPM)
IPM is a systems approach to reduce pest damage to tolerable
levels using a variety of techniques such as natural enemies,
genetically resistant plants, sound cultural practices, and, when
appropriate, chemical pesticides. The IPM approach is based on
proper pest identification, periodic scouting, and on the
application of pest management practices during the precise stage
of the crop's development when no control action would result in
significant economic losses. Two additional strategies of an IPM
approach are (1) Take pest control actions during the most
vulnerable stage of the pest's life cycle to maximize results
with the least possible effort, and (2) Use synthetic pesticide
spray applications for pest suppression only after all other pest
control alternatives have been considered and exhausted. The main
objectives of using alternative pest controls are to reduce the
high capital costs incurred with frequent pesticide applications
and to maximize the abundance of beneficial organisms.
Scouting
Periodic pest monitoring allows the producer to take control
actions on a timely manner based on stage of crop growth and on
pest population levels. This is more efficient than the
conventional calendar approach of pesticide applications which
consist of weekly sprays whether pest pressure is high or not.
Scouting consists of periodic field visits to take about five
random samples. Keep a written record of pest numbers, damage
levels, distribution in the field, and stage of crop growth at
each sampling date. This records will be helpful to develop
"in-house" economic threshold levels for the major
pests on the farm.
Pest management pointers
The best pest control program is that which takes preventive
action well before problem pests actually infest the field.
Knowledge of pest biology will further improve the grower's
ability to design the proper pest control preventive measures.
Successful growers are those which consistently pay attention to
detail in all areas of the IPM program (Table 6).
Table 6. Basic Techniques for Cucumber Pest Control and
Prevention
1. Use disease-free seed and soil.
2. Use resistant or tolerant varieties where possible.
3. Rotate with non-cucurbits.
4. Early detection of insect and disease problems.
5. Prompt removal of old crops from the field.
6. Apply recommended irrigation and fertilizer rates.
7. Proper weed management.
8. Clean farm machinery and tools to prevent soil-borne pathogen
spread.
9. Apply area-wide management strategies.
10. Properly recognize beneficial and pest organisms.
11. Use pesticides only when necessary.
12. Use registered pesticides with maximum effectiveness on the
target pest and with minimum adverse effects on non-target
organisms.
Insects
Important insect pests in cucumber include aphids, melon flies,
leafminers, whiteflies, and thrips. Other pests include spider
mites, caterpillars, and slugs. It is important to prevent or
minimize pest problems before serious outbreaks occur, to detect
pest problems early, and to select appropriate controls. The
judicious use of pesticides is important in the management of
resistance to pesticides, conservation of beneficials, minimized
environmental hazards, improved safety of workers in the field,
and overall reduced farm input costs.
Outbreaks of the silverleaf whitefly (previously referred to as
sweetpotato whitefly) and the greenhouse whitefly are currently a
major problem for cucumber production in Hawaii. Apply
insecticides only when necessary and, when possible, rotate
pesticide families to delay development of insect resistance.
Insects with exploding population growth rates such as thrips,
whiteflies, mites, leafminers, and aphids are especially prone to
develop pesticide resistance when exposed to frequent
applications of the same insecticide.
Aphids
Aphids damage cucumber plants by feeding on plant sap, and by
spreading important viral diseases such as papaya ringspot,
zucchini yellow mosaic, and cucumber mosaic. Feeding damage by
aphids can reduce plant vigor and may cause leaf deformation.
Heavy aphid feeding may encourage sooty mold growth. Viral
diseases spread by aphids can devastate cucumber crops. Aphids
have winged forms which can fly into crops and spread viral
diseases from weeds or infected plantings in this way. Aphids in
Hawaii are generally females which reproduce without mating. In
general, aphids can reproduce in one week and therefore several
generations are produced in one growing cycle.
For control, apply timely insecticide applications as needed
based on close monitoring of aphids and their natural enemies.
Aphid natural enemies include ladybird beetles, maggots of
syrphid flies, lacewings, parasitic wasps and fungal diseases.
Old crops should be promptly destroyed to reduce aphid movement
and the diseases they carry to healthy crops.
Caterpillars
Cutworms which include the variegated cutworm (Peridroma saucia)
and the black cutworm (Agrotis ipsilon), can devastate young
cucumber plants by chewing through the stems at the soil line.
Cutworms are active at night. Control is warranted when high
populations are present in the field before planting. Baits
containing Bacillus thuringiensis are available for cutworm
control. Control is normally not recommended when the plants are
>1 ft tall. Other caterpillar pests such as loopers have
generally been of minor importance in commercial cucumber
plantings.
Leafminers
Leafminers are small, yellow maggots that form trails beneath the
leaf epidermis as they feed. The adults are small flies, about
1/16 inch (16 mm) long, mostly black with some yellow markings.
The adult flies cause small, whitish stippling on the leaves as
they feed and lay eggs. The egg hatches in about 3 days and the
larva begins to mine the leaf as it feeds. After 4-7 days, the
larva drops to the soil to pupate.
Leafminers are normally a secondary pest that is kept in check by
natural enemies. However, both the vegetable leafminer (Liriomiza
sativae) and the celery leafminer (L. trifolii) may become
primary pests in cucumber fields where intensive pesticide use
has destroyed their natural enemies. This trend began in the
1950s where widespread DDT and closely related compound
applications eliminated the natural enemy populations of
leafminers. Tiny, wasp like parasites are the main natural
enemies of leafminers. Because of the establishment of effective
natural enemies and the resistance of leafminers to insecticides,
the major emphasis with leafminer management is the conservation
of its natural enemies. This means that registered pesticides
should be applied only when necessary and should be selected for
maximum control of the target pest with minimum adverse effects
on beneficial insects.
A monitoring program consists of placing white styrofoam or
plastic pans at the soil level below the plants throughout the
field to collect larvae as they drop and pupate. Insecticides are
recommended when average counts rise above 20 pupae/pan/day.
Yellow sticky traps can also be used to monitor leafminers in the
greenhouse. Thresholds need to be determined by the grower based
on the particular environmental and crop conditions. Because
contact insecticides won't reach the larvae inside the leaf,
systemic insecticides are recommended. Because of their high
reproduction rates leafminers are prone to develop resistance to
pesticides. The celery leafminer is more difficult to control
because it develops resistance to pesticides faster than does the
vegetable leafminer. For best results from pesticide treatments
use the recommended rates, rotate pesticide families when
possible, and obtain thorough foliage coverage. Cultural controls
include field or greenhouse sanitation, growing less susceptible
varieties, and weed control around the field to eliminate
alternate hosts.
Melon Fly
The melon fly (Bactrocera cucurbitae) has long been a major pest
of cucumbers in Hawaii. Melon fly damage occurs when adult female
flies lay their eggs into fruit and sometimes into stems. An
indentation often occurs at the site of oviposition and the fruit
may or may not become curved. The eggs later hatch into maggots
which live and feed within the fruit. Infested fruit frequently
rot, either in the field or after harvest. Attacks are severe on
young developing fruit, especially under high humidity conditions
after summer rains. This pest has traditionally been controlled
in problem areas with protein baits and an insecticide such as
malathion applied to corn border rows. An advantage of this
method is that insecticides for the melon fly are applied outside
of the cucumber crop and does not upset the balance of aphid and
leafminer natural enemies within the crop. The importance of
sanitation to manage flies cannot be over-emphasized. Melon flies
developing within the fruit from cucumbers and other fruiting
vegetables such as melons, squashes, peppers, beans, and tomatoes
may be major in-field reservoirs. Do not dispose of culled fruit
with live melon fly larvae in areas close to the production
field. Infested fruit left in the field will allow the melon fly
to complete its life cycle and cause further damage. Promptly
destroy old crops so that they do not serve as in-field
reservoirs. Alternate weedy hosts of the melon fly include wild
bittermelon or balsam pear (Momordica charantia L.), ivy gourd or
scarlet-fruited gourd (Coccinea grandis (L.)), teasel or hedgehod
gourd (Cucumis dipsaceus Ehrenberg ex. Spach), kupala (Sicyos
pachycarpus)., castor bean (Ricinus communis), spiny amaranth
(Amaranthus spinosus), rattlepod
(Crotolaria incana), and wild euphorbia (Euphorbia geniculata).
Wild bittermelon and ivy gourd are excellent melon fly hosts and
are important reservoirs for this pest. These weeds are also
reservoirs of important cucurbit virus diseases. Eight parasite
and 6 predators are known to be natural enemies of melon flies in
Hawaii but do not provide effective controls in commercial
produce operations.
Because of the prolific nature of this pest, organized area-wide
controls in vegetable producing areas are more effective than
single attack techniques followed by individual producers. The
following factors should be considered in an integrated melon fly
control program: 1) Evaluate population levels in and around the
field-- Populations are likely in areas where weed hosts such as
wild bittermelon and ivy gourd are present; 2) Honey-dew
secretions in or around the field from aphids, scales or
leafhopper feeding on foliage may attract melon fly populations
into the field; 3) Corn borders are more effective as trap crops
to attract melon flies in fields where alternate weed hosts are
not prevalent around the field margins; 4) Periodically monitor
melon fly populations through trapping.
Mites
Outbreaks of carmine spider mites (Tetranychus cinnabarinus)
occur occasionally, especially during hot, dry weather. Spider
mites feed on plant sap and prefer to live on the leaf underside.
Their feeding causes stippling of white areas on the leaves.
Heavily infested leaves may turn yellow and drop off prematurely.
Most miticides do not kill the egg stage so several applications
are required for effective control. Coverage is important to
reach the mites in the leaf undersides. Mites can be inspected
with a hand lens on the leaf underside. Natural enemies of spider
mites include ladybird beetles, and predaceous thrips and mites.
Varietal differences exist with respect to tolerance to spider
mite feeding, but no mite resistant commercial cultivars are
currently available.
Root-knot nematodes
Meloidogyne incognita are microscopic roundworms that feed on the
roots of plants. Foliage symptoms from the affected root system
include stunting, wilting, and leaf yellowing. Infested roots
develop gall-like swellings. Adult stages of the nematode live
inside these root swellings. These root galls prevent the normal
water and nutrient uptake by roots. Nematode numbers are often
higher in sandy soils under warm summer weather. Clean fields may
be infested by run-off irrigation water from nearby contaminated
fields and from movement of soil or infested plant material.
Soils may be tested to estimate parasitic nematodes populations.
Before planting, infested cucumber fields are normally fumigated
for nematode control. Several grasses that are non-hosts to the
root-knot nematode such as oats, barley, wheat, and rhodes grass,
may also be grown before cucumbers. However some grasses may
attract undesirable cutworm populations into the field. Cultural
controls to reduce nematode numbers include crop rotations,
fallow, field flooding, and destruction of volunteer weedy hosts.
No resistance is available to rootknot nematodes in the
cucurbits.
Other nematodes that infest cucumber are the sting nematode,
Belonolaimus spp., the root lesion or meadow nematode,
Pratylenchus spp., the stubby root nematode, Trichodorus spp.,
and the Pin nematode, Paratylenchus spp. Yield losses from these
nematodes range from moderate to heavy. In many cases nematodes
do not affect yields directly, but bacterial and fungal
infections may occur in root lesions caused by nematodes.
Stinkbugs
Stinkbugs of size from 1/2 to 2/3 inch in length feed on plant
sap and inject toxins on the plant while feeding. Heavy feeding
may deplete the plant of resources and reduce yields or make it
susceptible to disease attack.
Thrips
Thrips are small, <1/16 inch (15 mm) slender insects. Adults
usually have wings with feathery hairs that enable them to fly.
Many of the economically important species of thrips have
piercing-sucking type mouth parts and are not capable of rasping
plant tissue. In Hawaii, the melon thrips (Thrips palmi Karny)
and the Western flower thrips (Frankliniella occidentalis)
commonly infest cucumber plantings. Melon thrips tend to live and
feed on the leaves. Leaf edges tend to curl downward after heavy
thrip feeding. Serious damage often occurs during the early crop
stages. Population pressures can be especially high during hot
and dry conditions. Local research has shown that cucumber
tolerates substantial foliar damage before economic damage
occurs. Growers should protect their crops from damage levels (an
average of more than 9 thrips per leaf from sampling 50 randomly
chosen leaves in a small 0.5 Acre cucumber planting) early in the
season when the highest quality fruit and most of the total yield
is produced. The practice of weekly insecticide treatments to
suppress melon thrips when populations are low to moderate is not
warranted. Melon thrips are resistant to many organophosphate and
pyrethroid insecticides. Consult with your Agricultural Extension
Agent, Entomology Specialist, or agrichemical representative for
information on current effective registered pesticides.
Unlike the melon thrips which prefer to feed on the leaves, the
Western flower thrips tend to live and feed in cucumber flowers.
The Western flower thrips can cause fruit scarring when they feed
on immature fruit. Damage appears as silvery, web or streak like
scarring which may be accompanied by fruit malformation.
Laboratory analyses may be required to accurately identify the
thrips species present in your field. Natural enemies of thrips
include minute pirate bugs, spiders, and predaceous mites.
Whiteflies
The silverleaf or sweetpotato whitefly biotype B (Bemisia tabaci)
and the greenhouse whitefly (Trialeurodes vaporariorum) can build
up to high numbers in cucumber. A mixture of both whiteflies is
frequently found on cucumber. An accurate identification of the
whitefly species present is important in order to make correct
crop management decisions. High densities of the silverleaf
whitefly have caused various disorders in tomatoes, squash, and
leafy vegetables while similar densities of the greenhouse
whitefly have not. Growers should thus learn to distinguish
between the two major whiteflies. With some practice, growers can
distinguish the species by examining the pupal cases with a hand
lens. Whiteflies feed on plant sap and can reduce plant vigor and
yield when populations are very high. Both whitefly species
infest a very wide range of host plants including vegetables,
ornamentals, field crops, and weeds. Whiteflies, like aphids,
secrete honeydew, which is a sticky liquid that is a substrate
for sooty mold. Whiteflies have six life stages- the egg, four
nymphal stages (the fourth nymphal stage is commonly referred to
as the pupal stage), and the adult.
The silverleaf whitefly was so named because of the disorder it
can induce on certain cucurbits. On susceptible crops such as
squash, the leaf surface becomes silvered. The silverleaf
disorder, probably caused by a toxin injected by the whitefly,
has not been observed on cucumber. The average life cycle is 39
days from egg to adult but this period will vary with
temperature. The pupal case of the silverleaf whitefly is dome
shaped and has few filaments along its outer edge. The
sweetpotato whitefly transmitted gemini virus, which has resulted
in stunting and reduced fruit size in Florida and California, has
not yet been detected in Hawaii. These viral diseases remain a
great threat to Hawaiian agriculture. The average life cycle of
the greenhouse whitefly is 32 days from egg to adult but this
period will vary with temperature. The pupal stage is caked
shaped with many tiny filaments around the outer edge.
Both whiteflies are resistant to many pesticides. Insecticidal
soaps and oils are widely used for whitefly control. These
materials require thorough coverage of the leaf underside for
effective control. These insecticides are relatively mild on
natural enemy populations. Area wide control strategies are
necessary in areas where whitefly numbers are abnormally high.
Natural enemies include parasitic wasps, ladybird beetles, and
fungal diseases. Consult with your local county extension agent
or Entomology Specialist for an update on recent developments for
whitefly management and control
Diseases
Important diseases of cucumbers include the papaya ringspot
virus, zucchini yellow mosaic, watermelon mosaic, cucumber
mosaic, angular leaf spot, anthracnose, damping-off (Pythium and
Rhizoctonia root rot), leafspot, downy and powdery mildews and
scab. Once a disease has infested a crop, remedial action can be
taken, but it is usually already to late to prevent serious
losses. Field and seed selection, seed-treatment, rotations,
water management, weed control, insect control, and other
recommended sanitation practices and chemical treatments should
therefore be combined in a disease management program to prevent
disease attacks in cucumber. Seed treated with a fungicide can
protect the field from serious yield losses. Pay close attention
to fungicide application techniques. Coverage of all sections of
the field is important since unprotected spots may become
undesirable sources of inocolum. Fungicide sprays are usually an
integral part of cucumber production even when planting disease
resistant cultivars. Disease control has been improved when
fungicide treatments were initiated at the two true-leaf stage.
Other diseases of cucumber include wet rot, Choanephora
cucurbitarum; Alternaria leaf blight, Alternaria cucumerina;
Cercospora leaf spot, Cercospora citrullina; Sclerotinia stem
rot, Sclerotinia sclerotiorum; and Target leaf spot.
Angular leaf spot
The bacteria Pseudomonas syringae pv. lachrymans, occurs on most
cucurbits but is more prevalent in cucumbers. Outbreaks are
likely under continuous rainfall and 75-80F. First symptoms are
small, water-soaked angular lesions on the leaf underside.
Lesions, restricted between the small cucumber leaf veins, turn
yellow, develop yellow hollows, and finally disintegrate. Under
wet conditions, such as early in the morning bacteria oozes from
the lesions which later dries into a white crust. Expanding
leaves which are close to full size are most susceptible to
infection. Old leaves tend to be resistant. Young leaves can be
infected mechanically by insects or field workers. Infected
stems, petioles and fruits also develop water soaked lesions.
Fruit lesions are more circular, turn white, and crack open. This
openings allow for secondary infection by other organisms. The
bacteria survives on infected plant refuse and on seed. The
disease is spread by wind, rain, insects, and field workers.
Damaged plants with wounds from wind or sand are especially
susceptible to infection. Controls include a 2-3 year rotation,
use of disease-free seed, and weekly sprays of a broad-spectrum
fungicide such as chlorothalonil plus a copper fungicide. Be
aware that high copper application rates may result in crop
injury, especially during the early crop stages. Resistance or
tolerance is available in Centurion, Dasher II, Early Triumph,
Floracuke, Raider, Spring 440, Pointsett 76-S and other
commercial cultivars.
Anthracnose
Leaf spot lesions caused by the fungus, Colletotrichum orbiculare
(C. lagenarium), occur on leaves, stems, and fruits, resulting in
serious losses in cucumber, watermelon, and muskmelon. The
disease rarely affects squash or pumpkins. Lesions are
distinguished by the pinkish spore masses which develop in the
lesions. The symptoms first appear on the foliage as small,
yellowish water-soaked areas which later turn dark and dry out.
The lesions are not restricted by the leaf veins. Severely
affected vines usually die. Shallow brownish elongated lesions
develop on infected stems and petioles. Circular, black, sunken
cankers also appear on the fruits. Black specks appear on
enlarged fruit lesions, and under humid conditions.
Salmon-colored spores ooze from the black specks. Anthracnose is
spread by infected seed, wind, rain, insects, and by field
workers, especially during wet weather. The disease is soil-borne
for over 3 years and is also carried on volunteer weedy
cucurbits, such as Commelina diffusa, after harvest.
To prevent spreading the disease by plant refuse it is important
to destroy the crop immediately after the last harvest. Also,
five year rotations are recommended on anthracnose infested
areas. Weekly fungicide preventative programs at >100 psi are
recommended during humid rainy weather in areas where anthracnose
is a problem. Resistance is available in some cultivars such as
Dasher II, Pixie, Poinsett 76, Slice Master, and Sprint 440 II.
Bitterness
Bitterness, a physiological disorder, is often observed under
cool weather at higher elevations. At low elevations excessive
Nitrogen fertilization may result in this disorder but the causal
factor at higher elevations has not yet been determined. The
compounds cucurbitacin B and C are responsible for bitterness in
cucumber. They are normally found at higher concentrations in the
vines and in the fruit the chemical concentrates at the stem-end
just below the skin. The newer cucumber hybrids are less
susceptible to bitterness than older open-pollinated ones.
Damping-off
Fungal organisms which cause damping-off include Pythium spp.,
Rhizoctonia solani, Thielaviopsis basicola, Fusarium equiseti,
and others. Affected seedlings fail to emerge or collapse shortly
after emergence. Emerged seedlings affected by Pythium turn a
light green color and the cotyledons collapse. Water soaked
lesions also appear on the seedlings at the soil level. Lesions
caused by Thielaviopsis are grey to reddish but turn to a coal
black color. A red to brown rot is more characteristic in
infections caused by Fusarium. Humid conditions caused by close
planting, poor drainage, or by rainfall are conducive for
damping-off. Control for damping-off in the greenhouse include
proper soil sterilization and strict sanitation practices. In the
field cultural practices which improve drainage and wider
planting distances are recommended. High quality seed is
recommended but resistance to damping-off is not available.
Downy mildew
Optimal conditions for Pseudoperonospora cubensis are cool nights
between 55-75F and relative humidity >95. All cucurbits are
susceptible to this fungus but yield losses are most common in
cucumbers and muskmelons. Several strains of this disease may
exist in cucurbits. Initial lesions, which are limited by the
small leaf veins, include irregular to angular, pale green spots
which appear on the upper side of leaves near the plant crown.
The lesions then turn into yellow angular spots. The underside of
leaves later develop a downy white to gray mold, which may turn
gray to purple during wet weather. Spores develop in this mold.
The spores can be transmitted from plant to plant and from field
to field by wind. After spores infect a new leaf, lesions develop
in four to six days. The entire infected leaves eventually wither
and die. Plant stunting and poor fruit growth results under heavy
disease pressure.
The disease can be prevented with weekly fungicide treatments.
Sprays are less effective once the disease has appeared in the
field. Area-wide monitoring programs exist in other states in
which weather is monitored and growers are warned to start their
spray programs when the weather is conducive to downy mildew
outbreaks. Resistance is available in some commercial cultivars
such as Dasher II, Marketmore 76, Poinsett 76, Sweet Slice, Slice
Master, Sprint 440 II, and Gemini 7. Downy mildew resistance in
cucumbers is complex and involves several genes.
Gummy stem blight
Mycosphaerella melonis (Didymella bryoniae), causes lesions on
leaves and stems, and less frequently on the fruits. This fungus
attacks all cucurbits. Seedlings die rapidly if hypococtyls or
cotyledons are infected. In older plants lesions produce a
characteristic red or brown exudate at the crown of the plant and
along the vines. Black spores may be seen around the infected
tissue. Initial leaf symptoms are irregular circular dark spots
which may be surrounded by a yellow halo, and later dry up and
crack. Infection starts from the leaf margins and proceeds
inwards resulting in a typical leaf blight. Affected fruit have
small water soaked circular brown spots which have a greasy
appearance. Small black spores may also develop in these lesions.
The pathogen enters the plant through wounds caused by insects,
wind, sand or machinery. The organism survives on crop debris and
cucurbit seeds for a period of two years. High disease pressure
can be expected in the field and in the greenhouse under wet and
cool conditions.
Controls include soil sterilization and proper sanitation in the
greenhouse, weekly fungicide applications, rotations, and a
choice of drip instead of sprinkler irrigation. No resistance
exists on current commercial cultivars.
Powdery mildew
Powdery mildew caused by Erysiphe cichoracearum
(Sphaerotheca fuliginea), is a serious and common fungal disease
during warm and humid conditions with overcast days. Unlike downy
mildew, infestation and reproduction may occur under relative
humidity as low as 46. Infection can occur at 50F but is optimum
at 80F. All cucurbits are susceptible, but the disease is
normally not a problem on watermelons. Symptoms develop primarily
in 2-3 week old leaves and on stems. Younger leaves are almost
immune to powdery mildew. The disease is characterized by white
powdery-like growth, especially on the upper side of leaves, and
on stems (Figure 2). Affected leaves at first appear normal, then
lesions turn yellow to brown and dry out, resulting in early
leaf-fall of the older leaves. The disease is spread rapidly in
wet weather and a field may be wiped out in only a few days.
Fruit infection is rare, but occurs in cucumbers and watermelon.
The disease survives on volunteer cucurbit crops or weeds and is
carried over long distances by prevailing wind currents. Controls
include maintaining a healthy vigorous crop, removing volunteer
cucurbit crops and weeds around the field, sanitation, and weekly
fungicidal sprays. Recent data indicates that sodium bicarbonate
(household baking soda) and potassium silicate sprays may
effectively control powdery mildew, as well as other cucumber
diseases. Consult with your local county extension agent or
pesticide control specialist for current recommendations and for
an update on current EPA regulations on the use of these products
as fungicide sprays. Use of tolerant cultivar such as Milo,
Dasher II, Marketmore 76, Poinsett 76, Sweet Slice, Slice Master,
Sprint 440 II, and Gemini 7 offers some control.
Scab
The fungus Cladosporium cucumerinum affects all above parts of
the plant and produces the characteristic scab-like lesions on
the fruit. During humid weather a fungal brownish mat of spores
develops on the fruit. Most yield losses are caused by infections
of the fruit. It attacks muskmelon, pumpkin, and squash, but is
most serious on cucumbers. Initial leaf symptoms include numerous
angular, pale-green, water soaked lesions. The lesions turn brown
with necrotic margins and then turn gray or white. Petioles and
stems also develop elongated disease lesions and internode length
is often reduced. Disease spores are transmitted by wind,
insects, and by field workers and machinery. It survives in the
field on cucurbit plant refuse. Conditions conducive to disease
outbreaks are cool and humid weather. The disease may be
controlled with periodic fungicide sprays and by planting
resistant cultivars such as Dasher II, Calypso, Gemini 7
Marketmore 76, Poinsett 76, Slice Master, and Sprint 440 II. Scab
resistance in cucumber is by a single dominant gene.
Fruit or Soil Rots
Soil fruit fungal rot is caused mainly by Pythium aphanidermatum
and Rhizoctonia solani but also by Botrytis cinerea, other
Pythium species, and Rhizopus stolonifer, is a serious disease of
cucumbers in Hawaii. The disease results in up to 60% yield
losses. The disease infects fruit in contact with the soil
resulting in rotting and in fruit scars. Cottony leak, caused by
a Pythium spp., is the most common cucumber fruit rot in Hawaii.
Fruit symptoms include a soft and watery white fungus covering
the skin. Attacks of this fungus on young seedling also causes
typical damping-off. Soil rot in cucumbers caused by Rhizoctonia
is less common in Hawaii. Fruit lesions from Rhizoctonia begin as
dark-green water soaked areas, then affected tissues collapse
leaving small holes in the fruit which eventually dry-up. A
brownish mycelial growth on the lesions appears in affected
fruits during continuous humid conditions. Fruit rots are
partially controlled with trellises and plastic mulches.
Recommended cultural practices for Pythium control include
disking the soil 3-4 weeks prior to planting to completely
decompose old organic matter which helps to prevent the disease
organism from surviving in the soil. Fungicidal sprays may be
effective in controlling this disease. No cultivar resistance
exists to fruit rots in the cucurbits.
Viral Diseases
Viral diseases are among the major limiting production factors
for cucumber production in tropical areas. Typical symptoms
include green and yellow mottling and wrinkling of the leaves,
mottling and wartiness of the fruit, and general dwarfing of the
plant. Cultural practices developed in the 1950s included
planting of 50-100 ft border rows of non-susceptible crops such
as sweet corn, beans or eggplant. Growers should determine what
viral diseases are prevalent in their area of production and
select suitable resistant varieties where possible. Laboratory
analyses may be necessary to accurately identify the causal
agent(s). Enzyme linked immunosorbent assay or ELISA kits have
greatly simplified virus identification and are available at
diagnostic laboratories.
Papaya Ringspot Virus (PRV-W)
This virus attacks all cucurbits and is the number one viral
disease of cucumbers in Hawaii. Papaya Ringspot Virus Type W
(PSRV-W), was previously referred to as Watermelon Mosaic Virus
I. The virus also infects some weed and legume species. It
produces the characteristic virus interveinal chlorosis,
stunting, and misshapen fruits (Figure 3). In the field the virus
is transmitted by insects, workers, and farm machinery. Greatest
disease pressure is experienced during the summer months perhaps
due to the increased aphid activity. The best approach to manage
this disease is to use resistant cultivars. Some varieties claim
resistance to PSRV-W but have not been extensively tested for
disease or horticultural quality under local conditions.
Insecticide applications may reduce aphid numbers in the field
but this alone is usually not sufficient as a control strategy.
Other practices may include the use of reflective mulches,
elimination of volunteer weed hosts, and destroying cucurbit
plants in nearby fields.
Zucchini Yellow Mosaic Virus (ZYMV)
This virus, first reported in France and Italy in 1981, attacks
all cucurbits. Two different strains have been identified in
Florida and Connecticut. Symptoms include yellow leaves with
mosaic and a distorted appearance. The whole plant is stunted.
Affected fruit is also misshapen. Control practices may include
use of mineral oils, reflective mulches in the early aphid
infestation stage, control of alternate weedy hosts, and
insecticidal aphid control. Use resistant cultivars such as Sweet
Slice.
Cucumber Mosaic Virus (CMV)
This viral disease is of secondary importance to PRV-W and ZYMV
as a production problem in Hawaii. Several strains of this virus
attack all cucurbit crops, but watermelon is affected to a lesser
degree. Several weed species and crops from 12 plant families are
also infested by CMV. Apple of Peru, Nicandra physalodes (L.) and
Nasturium, Tropaeolum sp., are two weed hosts of CMV in Maui.
Other vegetables affected by CMV include tomato and pepper. All
of these plants show foliar symptoms when affected by CMV.
Affected cucumber plants are stunted while young leaves curl
downwards and develop a stunted, distorted appearance. Affected
fruit may turn a light green color and is also misshapen, mottled
and warty. For control destroy alternate weedy hosts close to the
field, control aphids with recommended insecticides, and use
resistant cultivars. Resistant cultivars include Milo, Centurion,
Dasher II, Elite, Early Triumph, Floracuke, Raider, and Sprint
440.
Weeds
Use an integrated approach to effectively manage weeds in
cucumber production. The IPM program for weed control uses weed
identification, monitoring, sanitation, alternative cultural
practices, and timely herbicide treatments. The first approach
for weed management is to avoid planting in fields that
experience heavy weed infestations. A weed map for each field
helps in the design of weed control measures and provides a
record of weed problems.
The benefits of proper field preparation can not be
overemphasized to improve cucumber growth and minimize weed
problems during the crop growth cycle. Even soil preparation,
proper soil moisture, and a pre-plant fertilized field will
improve stand establishment and early crop growth. Cultural
control practices for weed control include shallow cultivation,
plowing, disking, hoeing, crop rotation, cover cropping, living
mulches, organic or plastic mulches, and herbicides. For
effective weed control, herbicides need to be applied at the
correct rate and time. Therefore carefully read label
instructions to achieve maximum weed control with herbicide
treatments. Surface-applied herbicides normally require rainfall
or irrigation after application to maximize weed control
efficiency. Cucumbers have a poor competitive ability against
weeds, especially during the initial three weeks of growth. Weeds
are normally controlled through a combination of cultural
practices and herbicide treatments.
Pesticide applications should be conducted carefully because the
cucurbits are among the most sensitive vegetables to herbicides.
For planting selection sites, avoid fields with infestations of
troublesome weeds such as nutsedge and also of fields which have
received applications of herbicides such as Atrazine which is
likely to have unfavorable residual effects on cucumber growth.
Herbicides which may cause injury in cucumber because of
carryover include Atrazine, Lexone/Sencor, Bladex, Milogard,
Princep, Surflan, Cotoran/Lanex, Karmex/Direx, Lorox/Linex,
Classic, and Scepter. Laboratory tests are available to detect
Atrazine levels in cucumber leaves with apparent symptoms of
herbicide injury.
Successful weed control was obtained in Florida trials with a
pre-emergence herbicide application and two hoeings after
planting. One or two cultivations while cucumber plants are still
young also may provide acceptable weed control. The two hoeings
could be substituted with a post-emergence herbicide to achieve
similar effectiveness in weed control. Growing cucumbers with
plastic-mulch is an effective method of controlling weeds. Rows
between the mulch beds can be treated with registered
preemergence or postemergence herbicides for cucumbers, since the
cucumber roots may extend into those treated areas. Grassy weeds
of cucumbers in Hawaii include lovegrass, Eragostis pectinacea,
sandbur, Cenchrus echinatus, and wiregrass, Eleusine indica.
Broadleaf weeds include spiny amaranth, Amaranthus spinosus,
spineless (smooth) amaranth, Amaranthus spp., Flora's paint brush
(red pualele), Emilia sonchifolia, Orange pualele, Emilia
coccinea, jamaica vervain (joee), Stachytarpheta jamaicensis,
black nightsahde (popolo), Solanum nigrum, pigweed or purslane ,
Portulaca oleracea, richardia, Richardia scabra, sow thistle,
Sonchus oleraceus, spanish needle, Bidens piolosa, garden spurge,
Euphorbia glomerifera, swinecress, Coronopus didymus, and
tarweed, Cuphea carthagenensis.
HARVEST AND POSTHARVEST PRACTICES
Timing
Time from planting to first harvest is generally 45 to 55 days
for the Slicing types, and 52 for the slicing oriental types but
varies according to time of year, location and prevailing
weather. At higher elevations growth will be slightly slower due
to cooler temperatures. The crop is picked for three to as many
as 16 weeks depending on weather, plant vigor, and pest
incidence.
Production Yields
In Hawaii, the average slicing cucumber yields are about 20,000
lbs/Acre with 6,000 plants/Acre, a 100% increase over yields
obtained locally in the 1950s. Yields during the winter are
50-60% of those obtained during summer months. University of
Hawaii cultivars "Milo" and 'Lani" produced 11 and
8 lbs/plant, respectively, in Maui yield trials. Experimental
marketable yields in Hawaii range from 37-64,000 lbs/Acre. The
average Florida yield is 25,000 lbs/Acre with 17,500 plants/Acre.
Pickling cucumbers yields in California are about 40,000 lbs/Acre
with once-over harvest and population of 60,000 plants/Acre.
Maturity
Duration from pollination to harvest in slicing cucumber is 15-18
days, and 5-10 days for pickling cucumber. Cucumber plants set
fruit and develop over a long period of time, therefore
marketable fruit are ready for harvest over an extended period of
time. Size of marketable fruit for slicing cucumbers ranges from
6-10 inches in length and 1.5-2.5 inches in diameter. Slicing
cucumbers should be fresh, crisp, of medium size, well formed,
uniform and of a deep green color. Consult the Hawaii Grading
Standards for specific requirements. The fruit is picked before
it has reached full diameter and while the seeds are still small
and soft. A light green or yellow skin color is an indication
that the fruit is overmature for picking. Minimum market length
for European (parthenocarpic) cucumbers is 11 inches (28 cm) and
1.5 in (4 cm) diameter, and these weigh about 1 lb. Fruits from
trellised plants are uniformly green whereas fruits from
non-trellised plants may have a yellow-green side on the section
touching the ground.
Harvesting Operation
Cucumbers are picked manually. The fruit should be held near the
stem and clipped or snaped with a slight twist motion and not be
pulled off the vines to minimize "pulled ends." Pulled
off fruits leave an "open wound" where the fruit skin
is torn off, and this causes the fruit to shrivel around this
spot. The frequency of harvest is usually every other day or
daily during the warm months, and 2-3 times per week during
cooler weather or at higher elevations. Fruit quality is best
controlled when fruit is picked daily especially during warm
weather. Daily harvest is recommended for the oriental slicing
types. In large operations, cucumbers are picked in 40- to 50-lb
buckets and placed in bins, where a truck takes them to a packing
shed. An alternative harvesting operation consists of a conveyor
belt. Pickers in the field travel a few feet to the conveyor belt
where the cucumbers are placed and conveyed into a loading truck.
Bruising of fruit from excessive handling and unloading is
significantly reduced with the conveyor belt. Simpler harvesting
aids, including hand carts to hold picking containers also
improve harvest labor efficiency. Cucumbers should be kept in the
shade until taken to the packinghouse where they may be
hydrocooled, washed, sorted, graded, sized, packed, unitized for
shipment, and shipped to their destination market. For maximum
shelf-life, cucumbers should be pre-cooled after harvest at a 50F
(10C). For maximum harvest efficiency, instruct the field crew to
handle vines carefully during picking so that later fruit can
size properly, harvest only when the vines are dry to prevent the
spread of diseases, and remove larger fruits from the vine to
prevent the drainage of plant resources into these unmarketable
fruits.
Washing
Wash water management practices should be an important
consideration during the handling process to prevent the spread
of postharvest diseases. Decayed fruit should be culled to
eliminate potential sources of inocolum. Wash water is
chlorinated at 150 ppm, and fruits are held in this water for no
longer than two minutes in a single layer of floating cucumbers.
Packing
In the continental U.S. cucumbers are often waxed with one of
many commercially available formulations. Water loss may reduce
50% of fruit weight in non-waxed compared to waxed fruit.
Shrink-wrapping with polyethelene film, a common practice with
greenhouse European cucumber, also extends fruit shelf life by
preventing water loss. Cucumbers are normally sold in 55-lb
cartons or wirebound crates. U.S. Fancy cucumbers have a maximum
diameter of 2 3/8 inch and minimum length of 6 inches with a
straight shape and very little tapering. Important postharvest
diseases in cucumbers exposed to anaerobic conditions or to poor
ventilation include soft rot, Erwinia carotovora; bacterial spot,
Pseudomonas lachyrmans; Pythium aphanidermatum, and
Colletotrichum lagenarium.
Storage
Recommended storage for cucumbers include temperatures between
50-55F (10-13C) and 90-95 relative humidity. Average storage life
is 10-14 days. At storage temperatures above 55F (13C) the fruit
will ripen and turn from deep green to yellow. Chilling injury
occurs when fruit is held below 50 F (10C) for two days or
longer. Cucumbers are compatible in storage with such crops as
eggplant, grapefruit, limes, potatoes, and other cucurbits but
are not compatible with ethylene-producing fruits such as apples,
tomatoes, bananas, and muskmelons.
Market Information
In 1992 the state imported 2.3 million lb (1,036 MT) of
cucumbers, or 39% percent of the volume consumed locally. Over
3.5 million lbs are grown annually in Hawaii on about 250 acres.
The potential for the industry is to produce 100% of the local
demand during the summer and 60% during the winter months. If the
industry could produce 75% of local demand, the farm-gate 1994
value would be $2.7 million, based on production of 4.4 million
lb (2,000 MT) and the average per pound price of 46 cents.
A sound cucumber production program includes well planned
marketing. The prospective grower needs to have a good
understanding of annual market trends (Figures 4-7), market
competitors, consumer needs, potential buyers, and market
windows. To keep abreast of changing markets and new business
opportunities, producers need to be in close contact with fellow
industry representatives and with other business, university,
Cooperative Extension, and government organizations.
Essential to a marketing program is also a clear understanding of
the farm's financial situation at all times during the annual
production cycle. Updated farm financial records and the input of
financial information in budget generators will help the grower
to cut overhead and improve efficiency of production. Updated
financial information and well organized farm records are also
helpful in the loan application process, in assessment of crop
losses by unexpected pest outbreaks, and in making timely
production and financial decisions to take advantage of potential
investment opportunities or unexpected market windows.
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Notice: Reference to a firm or trade does not imply endorsement
over firms or products not mentioned.
Acknowledgements: We thank Dr. Kenneth Takeda for providing
important reference materials, and Dr. Bernie Kratky for critical
review of the manuscript.