CUCUMBER Cucumis spp.

FAMILY CHARACTERISTICS
    The cucurbit family includes species such as the gourd, watermelons, cantaloupes, squash and pumpkins.  Cucurbits are known as the vine crops due to their growth, habit, and culture.  Most plants in this species have a spreading growth habit with tendrils at the leaf axils. These plants are warm season, tender annuals, that require hot weather to develop fruit.
    Other family members include:
        Benincasa hispida L.; Uax Gourd
        Citrullus lunatus (Thung.) Mansf .; Watermelon
        Citrullus lunatus var. citroides (Bailey) Mansf.; Citron, Preserving Melon
        Cucumis anguria L.; West Indian Gherkin
        Cucumis melo L. (Chito group); Mango Melon, Garden Lemon
        Cucumis melo L. (Conomon group); Melon, Oriental Pickling Melon
        Cucumis melo L. (Flexuosus group); Armonian Cucumber, Japanese Cucumber, Uri
        Cucumis melo L. (Inodorus group); Melon, Muskmelon, Winter Melon
        Cucumis melo L. (Reticulatus group); Melon, Muskmelon, Cantaloupe
        Cucurbita maxima Dutch.; Winter Squash, Pumpkin
        Cucurbita mixta Pang.; Pumpkin
        Cucurbita moschata Poir.; Winter Squash, Pumpkin
        Cucurbita pepo L.; Winter Squash, Marrow, Summer Squash, Pumpkin
        Lagenaria siceraria (Mol.) Standl.; Bottle Gourd
        Luffa acutangula Roxb.; Angled Loofah
        Luffa cylindrica Roem.; Smooth Loofah
        Momordica charantia L.; Bitter Gourd, Balsam Pear
        Sechium edile S.W.; Chayote
        Telfairia spp.; Oyster Nut
        Trichosanthes anquina L.; Snake Gourd

CROP HISTORY AND DEVELOPMENT
    Cucumbers originated in India  between the Bay of Bengal and  the Himalayas.  They have been in cultivation for some 3,000 years, maybe being one of our oldest crops.  The cucumber was mentioned in the Bible, and was being grown in North Africa, Italy, Greece, Asia Minor, and other areas at the beginning of the Christian era.  In England the crop was first introduced in the 1300s, but not cultivated until 250 years later.  Columbus planted seeds in Haiti, and by 1539 cucumbers were grown in Florida by the natives, reaching Virginia by 1584. Today cucumbers are grown all over the world for pickling (picklers) and fresh markets (slicers).  Cucumbers grown in greenhouses have traditionally been grown near cities, mostly in the northeastern U.S.  The southwest has become an ideal place for greenhouse cucumber production because of high light intensities there.
    Cucumis sativus  Common slicing and pickling cucumber.  They are the same species, used differently, yet the flavor and texture are very similar.
    Cucumis anguria  are the Gherkin type that originated from West India
    Common Cultivars There are three major cucumber cultivar types produced today: processing (pickling), fresh market (slicing), and greenhouse (slicing). Cucumbers have become popular due to wide variety of fruit types and the use of these types in our diet.
    Processors: these fruit are blunt and angular, warty, and light green in color.  Pickling cucumbers have either black or white spines on their skin. ‘Conquest’ (F1 hybrid) and ‘Littleleaf’ are two superior pickling cucumber cultivars that have disease tolerance bred into them. Some other cultivars on the market in 1999 are the Bush pickle hybrid, ‘FanciPack’, ‘Cornichons’, ‘Saladin’ among many others.
    Fresh Market: usually longer, smooth rather than bumpy, and have more uniform green skin color who's skin is tougher than the picklers.  A few American slicing cultivars are ‘Jazzer’ (F1 hybrid), ‘Superset’ (F1), and ‘Marketmore’ (non-hybrid).  The ‘Fanfare’ hybrid, and the ‘Tasty King’ hybrid, are common Southeastern cultivars from Park seed.  The Salad Bush hybrid won the All America Selections because of its heavy yields, dark green fruit, and cylindrical 8 inch fruits.
    Specialty Fresh Market Cultivar- ‘Lemon’ is a pale yellow round cucumber that grows well in the southeast.  It is good for a specialty salad item.
    Greenhouse: British Columbia, Canada and the Pacific Northwest have been successful at growing different varieties of cucumbers in the greenhouses. Greenhouse growing in the southeast has a different environment and cultivars need to be chosen that would benefit from the local climate where they are being grown.  All cucumbers grown in the greenhouse are parthenocarpic and do not require pollination.  They are gynoecious cultivars which are all female.  The mideastern European  cucumbers are the best salad types of cucumbers that can be grown in the greenhouse.  They are tender, yet crisp fruits that are bitter free and require no peeling.  There are short types 'Beit Alpha' and long types 'Dutch Long'.   Some common early cultivars are the ‘Aria’ (F1), ‘Amira’ (F1), ‘Tyria’ (F1), and the ‘Early Perfection’ which is also a hybrid.  ‘Bronco’ is suitable for low light in early spring and fall crops.  A few more that have performed well are 'Sandra', ‘Boneva’, ‘Daleva’,  ‘Corona’, and ‘SweetSlice’.
    The new cultivars all have disease resistance bred into them.
    Production Locations  The major production states for fresh market are Florida, Georgia, North Carolina, South Carolina, New York, and California.  The main states that produce processing cucumbers are Michigan (Vlastic pickles), Wisconsin, North Carolina and Texas.   A total of 56,050 acres of fresh market cucumbers were harvested in 1997.  The amount of cucumbers consumed per capita in pounds has almost doubled from 1946 to 1992.
    For growing greenhouse production ideally there needs to be high intensity winter light, moderate winter temperatures, and easy access to markets.  The southwestern United States is a developing area for greenhouse production.

PLANT CHARACTERISTICS
    Overview. Cucumbers used for fresh market, greenhouse, and processing are of the same species, therefore have the same plant characteristics. The cucumber is a warm season annual vining plant that produces stiff hairs on the leaves and stems.  They can be rather itchy and irritating to human skin when touched.  This plant is herbaceous so it is easily susceptible to moisture stress.
    Root System. Cucumbers have moderately deep roots. Like many of the other cucurbits, the cucumber has a long taproot as well as a shallow fibrous root system, but it does not seem to be as extensive as others in this family.  The deep taproot will grow 36-48 inches (3-4 feet), but it will not branch out much below 2 feet deep.  Most of the fibrous feeders are in the top 2 feet and the active roots are concentrated between 8-12 inches.   A shovel will work fine to get a soil sample for the top shallow root system.  But a soil auger would be needed to find the fertility concentrations down at the bottom of the root system.  Yet for cucumbers most of the absorption of minerals takes place in the 8-12 inch range.   The taproot produces many rootlets that branch off about 1-3 inches from it.  As the plant matures, the root system becomes quite extensive, and the lateral root system can extend to a radius of 6-7 feet.  As the cucumber slows down in producing fruit, the deeper roots begin to senesce.  Adventitious roots will arise from nodal areas of the vine.
    Many cucumbers grown in greenhouses are grown hydroponically in troughs or tubes and plants are anchored in gravel, sand or soilless mixes.
    Stem.  The stems of the cucumber are vining, therefore can be trained on trellises to save space and improve yield and fruit quality.  Many large scale commercial growers find trellising uneconomical.  In greenhouse production they must be trellised.  The 4 angled stem is covered with the stiff hairs.  As soon as 2-3 leaves form, branching and vining begins.
    Leaves.  The leaves also produce the bristly hairs on them.  They are simple, alternate and lobed.  The leaves are triangular, palmate, and located at the base of the main axils.  Lateral tendrils also develop at the leaf axil.  The petioles are long (1.5-4.5 in.) and the leaves are usually 4-8 in. long.

Flower.  Perfect flowers are rare in cucumbers.  Many of the older cultivars are monoecious which means they produce separate male and female flowers on the same plant.  Most of the current cultivars are gynoecious  which has mostly female flowers (only about 5% are male).  In these plants, production of male flowers is promoted by long days and high temperatures.  Male flowers are also produced when the plant is stressed or has a high fruit load.  The grower can stimulate male flowering by applying gibberellin, which alters the plants auxin (hormones that control cell elongation) level.  Female flowers are produced during the short days with cool temperatures and low light.  Male flowers are produced in the axil of the leaf.  Female flowers are usually solitary.  The corolla is yellow, about an inch long, bell shaped, 5 petals, wrinkly and hairy.  Male flowers have 3 stamens with free filaments and anthers.  The female flowers have 3 united inferior carpels, with a style and 3 thick stigmas.   In gynoecious plants, pollination is usually done by blending seed of a monoecious cultivar in the field.  Most of the time its 88% gynoecious, 12% monoecious.

Developing cucumber

    Parthenocarpy.  This is when cucumbers set fruit without pollination, the fruit are therefore ‘seedless’.  The fruit really contains soft white seed coats.  This type of fruit set usually happens in low light, cool night conditions.  Greenhouse plants are parthenocarpic.  Pollination causes the formation of true seed, resulting in deformed fruit.  Most of the greenhouse cultivars originated in Europe.  The fruit are very elongate, cylindrical, and smooth, with thin and tender skin.  About 12-14 are produced per plant in the greenhouse.
    Seeds.  There are high quantities of seed per fruit.  They are small, flat and white.  This is not true in parthenocarpic varieties.  At temperatures of  70 °F, the seed will germinate in 5-6 days.  At 60 °F it will take from 9 to 16 days.   The quicker the seeds germinate and emerge, the less chance they have of being exposed to seed corn maggots and damping off disease.  About 35 seeds will constitute a gram, and approximately 1,000 seeds makes up an ounce.  It will take about 16,000 cucumber seeds to make a pound.  The seed should be planted 1-2 inches deep in the soil.
    Pollination.  Insects are required for pollination in cucumbers.  Honey bees are the primary pollinators in the field.  Many times, farmers transport their bees from field to field to do the pollination.  The monoecious cultivars, which are plants having male and female flowers, need one hive of bees per 50,000 plants.  When the new gynoecious hybrids are available they will need 2 to 3 times the amount of bees, and they will need to be interplanted with monoecious plants.   The pollen of cucumbers is sticky and heavy and the flowers only open for one day.
    Bees. It is important not to disturb bee activity, which is mostly in the morning.  Bees are highly susceptible to pesticides. This is because the pesticides get mixed in with the pollen and the bees take it to the hive and store it and feed it to their young.  Pesticides should be sprayed late in the day or at night, when there is little bee activity.  The colonies of bees should not be set out until 3 to 6 days after flowering.  If the bees are set out too early and there are not enough blossoms then they will be attracted outside of the field and will not be as effective at pollinating the crop of cucumbers.
    Cucumber plants will produce uniform fruit when pollination is sufficient.  It is also good to have a water source within 0.25 miles of the field for the bee colony. Uniform fruit development is a primary requirement for mechanical harvest.

PROPAGATION METHODS
    Overview.  Cucumber seeds do not germinate in soil where temperatures are below 52 °F.    The seed are directly planted in to the field.  The seeding rate is about 3 pounds per acre.   The seeds of slicing cucumbers are drilled in rows 4-6 feet apart and after thinning have 8-20 inches in between plants.  The final plant population should be from 5,200 to 21,800 plants/acre for fresh market, depending on whether it is hand or machine harvested.   Pickling cucumber seeds are drilled 2-3 in deep with a 3 to 4 foot spacing between rows.  These plants are subject to one final destructive harvest. There should be about 43,600 to 87,100 plants/acre for pickling cucumbers.  Some farmers will plant 150,000 plant/acre with irrigation and machine harvest.
    Temperature  The optimum daily temperature is 65-75 °F.  Cooler temperatures will slow down growth and slow growing seedlings are susceptible to flea beetles who chew on the leaves and reduce leaf area.
    Young plants are susceptible to cool weather, cold soils, and wind erosion after germination.
    Windbreaks of grass are effective in the field to reduce soil movement and protect the seedlings.

CULTURAL PRACTICES

Overview. Cucumbers require warm temperatures, irrigation, weed control, and disease and insect management for maximum production.     Soil Type.  Cucumbers require a light friable soil that is well drained for maximum yield.  Soils that are sandy, silty, or  clay loam should be enriched by tilling in a cover crop or animal manure.   Heavy soils or poorly drained soils are not suitable for the production of cucumbers.   The cucumber needs well drained soils because they do not perform well under anaerobic conditions.  The cucumber plant can tolerate somewhat acid soils, but have maximum fruit set and growth between a pH of 5.8 to 6.8.

Cucumber field

    Fertility.    Before planting, nitrogen should be applied to the field at 40 to 60 lb/acre, phosphorus should be applied up to 150 lb/acre, and potassium up to 200 lb/acre.   When taking a sample of the crop to perform a fertility analysis in greenhouse production, collect 15 mature leaves from new growth. For collecting out in the field get 12 leaf blades that are located 5th leaf from the tip.  When the plants are vining rapidly, they can be side dressed with 45 lb of N with at least 50% of the N in the nitrate form.  Nitrate can be stored in the plant or be incorporated into organic molecules by the enzyme nitrate reductase.  Broadcast application of fertilizer is recommended for the cucumber plant, perhaps because banding with direct seeding could damage the plant.  Broadcast is also better for the spreading habit of the cucumber roots.

    Nutrient deficiencies (photos provided by APS press)

Magnesium deficiency - older leaves are chlorotic beginning at leaf tips and between veins

Potassium deficiency - mottled chlorosis on leaf tips of older leaves that become necrotic

Nitrogen deficiency

Boron toxicity

    Greenhouse Fertility.  Phosphorus should be applied pre-plant at a rate of 200-400 lb/ac of P₂O₅.  Both phosphorus and potassium should be applied 8-12 inched deep in the soil.  About 50 lb/ac of elemental nitrogen should be applied before planting.  Additional nitrogen should be applied as side dressings or through irrigation as needed.
    Weed control.   Early in the season it is easy to control weeds by cultivation.  Once the vines grow and merge with other rows this practice is not feasible.  Most of the fresh market growers use a black plastic mulch, either as a full bed mulch or as strips on either side of the row. In cool climates, the black plastic can help in keeping the temperatures warmer and moderating moisture in the soil.  Herbicides are used for full season weed control.
    Irrigation.  Cucumber is a quick growing crop that produces a lot of succulent growth. The crop must be supplied with plenty of moisture for its vigorous growth.  Cucumber plants especially need water during blossoming and fruiting.  Any stress during blossoming could cause the blossom to abort.  On average, cucumbers need 1 inch of water a week.  During hot, dry weather and during blossoming the cucumber may need 2 inches a week.  In the south where it is humid, overhead sprinkler systems are used.  If using this type of irrigation, there should be enough time for the leaf to dry before nightfall to decrease disease potential.  During the blossom stage, it is important not to disrupt bee activity with overhead irrigation, because of the important role bees play in the pollination of field grown cucumbers.  In arid parts of the country, furrow irrigation is used to decrease water loss due to evaporation.
    Greenhouse Training. A string can be placed horizontally along the bed, 7-8 feet above the bed.  The base of the string can be loosely tied to the base of the stem.  As the stem grows it can be fastened to the string with clips.  As one stem develops, all the laterals and tendrils should be removed as well as fruit buds from the first five leaf nodes.  When the stem reaches the horizontal support wire, it can be trained down the wire and down another string between two plants in a row.  The stem is then trained back up the original string with out ever touching the ground to form a full circle.  Fruit should develop at each node and should continue for 60 days

INSECTS
    All crops produced are susceptible to insect damage.  Many of the vegetables in the cucurbit family are susceptible to the same insects.  In the early stages of growth, the cucumber plant is susceptible to the flea beetle that greatly decreases leaf mass and inhibits photosynthesis. Aphids can kill young plants and they also carry mosaic disease.  Aphids attack plants in late spring to early summer and spread very quickly.  The pickleworm, Diaphania nitidalis, found from Canada to South America feeds on foliage, flowers and fruit.  The adult moth lays its eggs on the foliage and the larvae migrate all over the plant.  The affected fruit rots and can no longer be consumed by humans.
    The cucumber beetle is one of the main threats to the crop.  The adults lay eggs at the base of the plant, the larvae hatch and feed on the roots for 2-4 weeks, then emerge as adults. The striped cucumber beetle is able to over winter, while the spotted beetle migrates from the south to the north.
        -Eastern Spotted cucumber beetle- Diabrotica undecimpunctata howardi- is ¼ inch long, has a black head, brown and yellow antennae black legs, and a yellowish green body with wings that have 12 distinct spots.
        -Striped cucumber beetle- Diabrotica acalymma vittatum- is 1/5 inch long with a black head and striped yellow and black wings.
        -Banded cucumber beetle- Diabrotica balteata- The cucumber beetle chews the leaves, blossoms and fruit.  As the adults feed on the crop they may spread bacterial wilt and mosaic, which are two serious diseases.
    Non-Chemical Control.  For non-chemical control, covering the vine plants with polyester row covers at planting has protected plants from the beetle.  When the blossoms appear, the grower removes the covers to allow pollination.  Cucumber beetles also feed on corn, so it would be beneficial not to plant corn next to the cucumber field.  The tachinid fly, Celatoria diabtoticae, is a natural predator of the cucumber beetle that could help reduce population levels.
    Chemical Control.  Water quality must be considered when utilizing chemicals for controlling insects.  Many chemicals are also very toxic to bees, so spraying should be limited during bee activity.  IPM (Integrated Pest Management) is a technique used by growers to reduce the amount of chemicals sprayed therefore reducing costs and pollution. Selecting the right pesticide for your conditions and crop can have a minimum adverse affect on the environment and control the insects better.
    Other pests include the leaf miner, nematodes and cutworms.

DISEASES
    Cucumbers have been bred with disease resistance to several important diseases.  Anthracnose, Angular Leaf Spot, Bacterial wilt, Downy Mildew, Cucumber Mosaic Virus, Powdery Mildew, and Scab. F1 hybrid cultivars help control the disease, they do not eliminate the disease completely. Choosing resistant varieties, providing favorable growing conditions, controlling insect pests, and plowing or removing and composting plant refuse will all help in keeping disease population under control.

Anthracnose. Colletotrichum lagenarium, is a fungus that affects leaves, stems and fruit.  Starting at the leaf margin, this disease moves its way inward turning the leaf brown as it goes.  Elongated lesions are found on the stems, and the leaf material beyond the infection point may die.  Fruit develop a pink ooze in the center and sunken lesions on the outside of the fruit.  The seed carries this disease, as does the plant residue. Therefore, using clean seed and rotating crops could be a affective means of control.

Anthracnose

 

Angular Leaf Spot. Pseudomonas lachrymans is a bacteria that develop on leaves and fruit. The fruit have small sunken water soaked lesions that become susceptible to secondary rots.  The leaves become irregular in shape and get veining patterns. It over winters in seed and plant debris.

Angular leaf spot

 

Bacterial wilt.  Erwinia tracheiphila is present whenever the striped, banded, or spotted cucumber beetle is feeding on the plant.  This bacteria can be present as soon as the plant emerges but is not usually visible until the plants branch, flower, and set  fruit.  This disease can be identified by cutting a stem in half and pulling it apart, seeing a string of ooze connecting the parts.  This disease can only be controlled by controlling the cucumber beetle.

Bacterial wilt (photo provided by plantpath.ifas.ufl.edu)

    Downy Mildew.  Pseudoperonospoa cubensis  is high in pickling cucumbers because they are planted at such high densities.  Yellow and brown spots appear on the upper leaf surface, with a purplish mold on the underside. It is wind borne so it is practical to use resistant varieties.
    Cucumber Mosaic Virus.  The plant is stunted and foliage is mottled followed by occasional wilt and death of leaves.  It is vectored by aphids and the cucumber beetle.
    Powdery Mildew.  Erysiphe cichoracearum is an airborne fungus that is serious in warm areas and in the greenhouse.  First, white powdery spots appear on the leaves, then the plants wither and die.
    Scab. Cladosporium cucumerinum is a fungal growth that appears as dry corky lesions on the fruit.  This disease will grow well in cool night weather that is moist and humid.
    Other diseases

Belly rot - Rhizoctonia solani

Belly rot

Fruit rot (photo provided by plantpath.ifas.ufl.edu)

Fruit rot

Gummy stem blight - leaf

Gummy stem blight - stem

Fresh Market.  Harvesting for fresh market is a repetitive process.  The slicers are picked by hand often, because if old fruit is allowed to remain on the vine it will decrease young fruit production.  It is possible that some fruit will be too large to market twelve days after the first female flower opens. The fresh market cucumbers need to be less than 2 3/8 inches in diameter when harvested.  The length should be a minimum of 5.5 inches and can be up to 6-9 inches.  Cucumbers grow very quickly and in warm weather can have a 40% increase in weight in 24 hours.  Generally these fresh market cucumbers are harvested every 2-3 days.

Harvesting a cucumber field