B's Cucumber Pages
Commercial Cucumber Production
From Producing Vegetable Crops by Swiader, J.M., G.W. Ware, and J.P. MacCollum. Danville, Illinois: Interstate Publishers Inc. Chapter 17, Cucumbers.
From Producing Vegetable Crops by Swiader, J.M., G.W. Ware, and J.P. MacCollum. Danville, Illinois: Interstate Publishers Inc. Chapter 17, Cucumbers.
The major portion of the commercial crop in the U.S. is for processing, with Michigan, North Carolina, Texas, California, and Wisconsin the leading states for pickle production. Processing cucumber yields average about 5 tons per acre in the U.S., and range from about 4 tons per acre in the East to over 18 tons per acre in California. Approximately 40% of the pickling crop is fresh-packed, 15% is refrigerated, and 40-45% is brined. Cucumbers for pickling are usually grown under contract, so profits are directly related to yield per acre.
Florida, the Carolinas, and Texas lead in fresh market production. Average yields for fresh market slicers picked by hand range from 3 tons per acre in parts of the eastern U.S. to over 16 tons per acre in California; top yields can be much higher. Fresh market cucumbers produced early in the marketing season are a high-value crop in most areas of the U.S.
Worldwide, cucumbers are extensively grown, with most of the crop used for fresh market. China leads in production, followed by India, the USSR, the U.S., and various European countries. In addition, there is some greenhouse production, particularly in northern Europe and Japan, and to a lesser degree in the U.S. and parts of the Middle East.
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New cucumber types incorporate a gynoecious flowering habit, whereby only female flowers are produced. These hybrids, often referred to as "all-female," tend to be early in maturity, outyield standard cultivars, and produce a concentrated fruit set, making them well-suited for mechanical harvest.
Somewhat similar to the gynoecious lines are the predominantly female types, commonly referred to as "PF" cultivars. These hybrids are not completely gynoecious but produce some male blooms. The "PF" expression is more typical of most present-day gynoecious hybrids. The number of male flowers is generally far less than those of monoecious plants, but can vary widely depending on cultivar and environmental conditions. The highly female expression of the hybrid "PF" plants concentrates fruit set so plants are well suited for once-over harvest.
Sex expression in cucumbers can be modified by the use of several chemicals. Silver nitrate and gibberellic acid will promote male blooms on gynoecious plants. The growth regulator ethephon induces female flowering and causes monoecious plants to exhibit gynoecious expression.
Environmental factors can also have significant influences on sex expression in cucumbers. High temperatures and long days favor male blooms, while short days and low temperatures promote female flower development. As a general rule, environmental factors that result in stress in the plant, such as increased plant populations and low moisture, will tend to increase male flowering in "PF" types and will sometimes cause some male flowers to develop in gynoecious lines.
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Some cucumber cultivars are able to set fruit without pollination and sexual fertilization. These are known as parthenocarpic fruits and are used primarily in greenhouse production. Parthenocarpic fruits do not have seeds, even though occasionally some seeds may be present. In order to obtain normal fruit growth and development, parthenocarpic cultivars must be sprayed with a fruit-setting hormone, such as chlorflurenol. Some newer cultivars contain a gene for parthenocarpy and do not require hormone sprays for fruit set.
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Cucumbers can be grown on a wide range of soil types, provided they are well-drained. A light loamy sand which contains moderate to high amounts of organic matter is best for the early crop. Heavy soils can be used for commercial production, although fruit quality may be adversely affected because of poor drainage. Although cucumbers are fairly tolerant of acid soils, best growth is obtained in the pH range of 6.0-7.0. The young plants are very susceptible to herbicide residues in soils from previous crops, especially triazine residues. Potential growing sites should be checked for herbicide carry-over if the previous cropping history of the sites is not known.
Cucumbers are a quick-growing and succulent crop and must be well-supplied with nutrients and moisture for vigorous growth. Fertilizer requirements will vary depending on soil type, native fertility, previous cropping, cultural practices, and yield levels. Machine-harvested gynoecious hybrid cultivars grown for processing, which mature in 40-50 days, require less fertilizer than hand-harvested monoecious cultivars grown for fresh market, which have a considerably longer growing season. The higher plant populations now being used with machine harvest, however, increase fertilizer requirements, so fertility rates for both machine- and hand-harvested plantings may be comparable.
Nitrogen fertilizer recommendations range from about 75 pounds per acre on some heavy, dark-colored soils to 150 pounds per acre for lighter soils. Phosphorous and potassium fertilizer recommendations depend on soil test levels. On sandy soils where leaching is likely to occur, one-half the nitrogen is applied close to planting, and the remainder is sidedressed in several applications when the vines start to fill the rows. To avoid damaging the roots, no more than 40 pounds of nitrogen (or potassium) should be sidedressed at any one time. Where irrigation is used, nitrogen and potassium are sometimes applied through the irrigation system.
The most important micronutrients are zinc and manganese. Deficiencies of these elements are most likely in alkaline soils and under high phosphorous fertility. A standard practice of growers in some regions is to make foliar application of both manganese and zinc 2-3 weeks after seedling emergence.
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Plant population and spacing depend on the availability of soil moisture and the harvest method. Higher populations are used with destructive machine harvests to maximize yields, but they require more intensive management and grower skill. Pickling cucumbers usually have smaller vines than slicers and are grown at higher populations. With irrigation and machine harvest, populations of over 150,000 per acre are used. On light-textures soils and no irrigation, machine-harvested plantings will have 30,000-60,000 plants per acre. Plant populations for slicers picked by hand generally range from 7,000 to 20,000 plants per acre.
For hand-harvested crops, the seed is planted with standard corn or bean planters 05-1.5 inches deep, and later thinned. Deeper seeding is used on light-textured soils to place the seed in contact with soil moisture; however, too deep seeding may result in delayed emergence and poor stands. Row spaces vary from 30 to 60 inches, with plants spaced 8-15 inches apart. Generally, the wider spacings are used with fresh-market slicers.
For machine-harvested crops, precision seeders are used to plant the higher populations, to allow the grower to plant a desired stand and eliminate thinning costs. Row spacings vary from 12 to 30 inches, with plants 2-6 inches apart. In California, twin-row production on 40-inch beds is used to increase plant populations. The two rows are spaces 12-14 inches apart on the bed, with plants spaced 2 inches apart in the rows. Since there are more plants per acre and more competition between the plants, twin-row production requires more precision and closer management.
Fresh-market cucumbers (slicers) are sometimes transplanted for early production. Transplants should be grown in specialized containers such as peat pellets or peat pots and should be no older than 3 weeks when set in the field. Special care should be taken so as not to damage roots since this will greatly delay the development of the crop. For early plantings of slicers, row tunnels and plastic mulches have proved very effective in cooler climates for increasing early growth response. A small number of fresh marker cucumbers are still planted in hills. with this method, several seeds are planted in each hill, and later thinned to three or four plants.
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In order to ensure successive harvests, some growers will schedule their planting dates based on the size or physiological age of previously planted cucumber seedlings. As a general rule, later plantings are made when the seedlings from the previous crops have the first true leaf showing between the two cotyledons. This method works reasonably well for the first part of the growing season. Towards the middle of the season, as temperatures rise and growth rate increases, the schedule must be adjusted and subsequent plantings made when approximately 80% of the seedlings of previous plantings have emerged.
Heat unit systems are also used in cucumber production to space planting dates for successive harvests. By knowing the number of heat units required to reach first harvest for a crop type and maturity group (early, mid-season, late), a grower can schedule plantings based on heat summations so that one harvest would be finishing as another was about to begin. One system uses a base temperature of 60F and a ceiling temperature of 90F. Another system determines heat units by subtracting a base temperature of 55F from the daily mean temperature. Cultivars differ in heat units required to reach maturity, and some variation may be expected for both location and season.
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Herbicides are used to control weeds when close plantings and high populations make cultivation difficult and where high weed pressures exist. Most herbicides available today tend to provide more effective control on grasses than broadleaf weeds. Usually the best results are obtained by using combinations of herbicides. However, cucumbers are very susceptible to injury from many herbicides, and even at labeled rates of application, this safety margin is relatively narrow.
Timely cultivation can provide effective weed control, where row spacing and vine growth allow. Up until the third- or fourth-leaf stage, close cultivation can be accomplished without undue damage. Once vines start to run, mechanical cultivation should be shallow and not too close to the plant. Hand weed control is sometimes practiced, depending on the size of operation and the availability of labor. When earliness is desired, black polyethylene mulch can be used to increase soil temperatures for fresh market crops, and in the process, control weeds and conserve soil moisture.
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Most irrigated production is on sandy soil or on heavy-textured soil in arid climates. Irrigation permits high-density planting and will generally be needed, even on soils of relatively high-moisture-holding capacity, to reach the maximum yield potential as plant populations increase to 100,000 plants per acre or more. Crop moisture requirements range from 15 to 24 acre-inches of water, depending on climate, soil type, plant populations, and market type. On the average, cucumbers need 1 inch of water each week, which may increase to 2 inches per week during hot and dry weather, or if plants are fruiting. In arid areas, furrow irrigation is preferred to reduce evaporation losses, while in humid regions, overhead sprinkler or gun-type systems are used. Where possible, overhead irrigation should be timed to allow leaf surfaces to dry before nightfall. Irrigation should be scheduled so as not to interfere with bee pollination in the mornings during flowering.
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Cucumber flowers normally open only one day. Bee activity is generally greatest in the morning up until early afternoon. Wet, cool weather significantly reduces bee activity and is a major reason for poor fruit set in certain years. Overhead irrigation is detrimental to bee activity, and during flowering watering should be withheld until late in the day or at night if possible.
Bee colonies should not be placed in the field before the first female flowers appear. If placed too early, the bees will visit plants in bloom outside the field and be less effective on the cucumber crop to be pollinated. In experiments with cucumbers for machine harvest, delaying pollination for as much as 12 days resulted in a significant increase in the number of fruits per plant. Generally, colonies should not be set out until 3-6 days after blooming starts. This ensures that flowering will be sufficiently well along to attract bees and will result in a more concentrated and uniform fruit set. Also, for maximum pollination, bee colonies should have a nearby source of water, preferably within 0.25 mile of the site.
Highly toxic insecticides applied to other crops will kill bees visiting the crop. Bees are attracted to sweet corn when it sheds pollen and are easily killed by carbaryl applied for earworm control. The carbaryl remains highly toxic to bees for several days, since it is mixed with pollen, which bees store in the hive to feed their young. Insecticides should be applied late in the day or at night when there is little or no bee activity.
Contrary to popular belief, cucumbers, melons, and squash will not cross-pollinate with one another; however, cultivars within each species will inter-breed.
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Fruits for fresh market slicing are preferably long, smooth, straight, thick-skinned, with a uniform medium-dark green color. Pickling fruits are lighter green in color, shorter, thinner-skinned, and characterized by a warty surface. Fresh market cultivars have fewer spines than processing types. Each type should be cylindrical with blocky ends, although rounded ends are also acceptable for slicers. Greenhouse cultivars should have long, relatively narrow fruits, with rounded ends. Dutch greenhouse cultivars are parthenocarpic with gynoecious expression and high-yield potential, while Japanese greenhouse cucumbers are mostly monoecious. Unlike those for processing and some slicing, greenhouse types are fairly smooth-skinned.
All commercial cultivars have either black or white spines on the fruit surface, a trait related to fruit maturity. White-spined cultivars are generally slower in their rate of development and retain their green color and firmness longer than black-spined fruits. Cultivars with black spines tend to turn yellow prematurely, especially under high temperatures, and produce larger fruits that soften with maturity. Consequently, black-spined cultivars are used for pickling in regions where summer conditions are relatively cool. White-spined hybrids have largely replaced black-spined cultivars in warmer growing regions and in areas where once-over machine harvesting is prevalent.
For processing cucumbers, the grower generally has little choice of cultivar since the processor selects and provides the cultivars to be grown. Gynoecious hybrids are grown for just about all machine harvest. These types have also replaced many of the standard monoecious types that were previously used in hand-harvesting pickling cucumbers. For fresh market slicers, both monoecious hybrids and gynoecious hybrids are available. Vigor, uniformity, and higher yields are some advantages of hybrids over previous open-pollinated monoecious cultivars. Regardless of how they are to be used, cultivar differences in earliness and disease resistance are also important considerations for cultivar selection.
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Cucumber Beetles. The striped (Acalymma vittatum) and spotted (Diabrotica undecimpunctata) cucumber beetles feed on the foliage and later on the fruit. Both can transmit bacterial wilt, and the striped cucumber can also spread cucumber mosaic virus (see Diseases). Larvae feed on roots and stems. Both beetles are about 0.25 inch long. The striped cucumber beetle has a black head and black- and yellow-striped wings, while the spotted cucumber beetle has a black head and a yellowish-green body with twelve black spots on its back. The adults appear in the early spring and feed on the cotyledons and new leaves. Rapid germination and seedling development will sometimes allow the plants to outgrow the severity of damage, once vines start to grow.
Pickleworm. This is a destructive insect pest during July and August. The worm is a bright-colored larva with numerous black dots over its body. It is found in the southeastern part of the country and in major production areas of North Carolina, but it may be destructive as far north as Michigan and New York. The worms feed on flowers and leaf buds and will tunnel into vines and fruits. They must be killed before they enter the fruits; once they are inside they will not be found until after the fruit is processed. Weekly insecticide applications should begin at the first sign of damage.
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Angular Leaf Spot. From the bacterium Pseudomonas lachrymans, angular leaf spot causes small, angular, water-soaked or tan-colored spots on the leaves and fruits. The organism overwinters in plant refuse, soil, or seed and is favored by warm, wet weather. Resistant cultivars should be used to help control the disease.
Mosaic. Also referred to as "white pickle," mosaic is a viral disease found in many areas throughout the country. It is characterized by stunting of the plants, mottling, yellowing, and wrinkling of the leaves, and warting and mottling of the fruits. Sometimes plants outgrow symptoms. Mosaic affects other cultivated plants such as muskmelons, squashes, peppers, tomatoes, and celery. The organism also attacks several wild plants, including pokeweed, milkweed, catnip, and ground cherry. It overwinters on roots and seeds and is spread by aphids and striped cucumber beetles. It can also be spread by personnel working among infected plants and then carrying it to new fields. Eradication of wild host plants and control of insect vectors are important in the control of mosaic. Some cultivars are resistant to mosaic.
Scab. Scab is caused by the fungus Cladosporium cucumerinum which produces sunken, dark brown spots on the fruits. In moist weather, the spots will be covered with a greenish mold. A gummy substance oozes from the fruits. The leaves and stems may also be affected. The fungus also attacks muskmelons and pumpkins. The disease occurs primarily in the north-central and northeastern states and is favored by cool, moist weather. The organism overwinters in old refuse and on the seed. The best control measures are the fixed copper fungicides, 2-year rotation, and resistant cultivars.
Bacterial Wilt. This disease is caused by the bacterium Erwina tracheiphila and appears as a progressive wilting of the plant and eventual death. It can be recognized by a sticky, stringy ooze that can be squeezed from the cross section of a diseased stem. The organism overwinters in cucumber beetles and is spread by their feeding on the plant. Dry weather and temperatures of 50-70F favor beetle migration and feeding. There are no resistant cultivars, and the best preventative measure is to control cucumber beetles with timely insecticide sprays.
Gummy Stem Blight and Black Rot. Gummy stem blight (Didymella bryoniae) refers to the stem phase of the disease, and black rot (Phoma cucurbitacearum) refers to the fruit stage of the disease. A fungal disease, it can infect the plant at all stages and inflict severe damage, ultimately resulting in death. On fruits, lesions appear as small, water-soaked spots that grow into large, sunken lesions. The fungus can overwinter in all parts of the U.S. and can be seed-borne. Therefore, clean seed and rotation are important elements of control. Resistance is available, but fungicides are important, even at early stages of plant growth.
In addition to the above diseases, cucumbers may be infected by downy mildew, anthracnose, root knot (caused by nematodes), damping-off, powdery mildew, gummy stem blight, and Alternaria and Cercospora leaf blights. Downy and powdery mildew are not as widespread as they previously were, since most commercial cultivars are resistant to or tolerant of these diseases. Damping-off is a disease complex (Pythium sp., Fusarium sp., Rhizoctonia solani) similar to that causing root knots in beans. Anthracnose, Alternaria, gummy stem blight, and root knot are also major diseases of melons. Presently, there are no resistant cucumber cultivars for damping-off, gummy stem blight, or leaf blights.
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The slow acceptance of once-over machine harvesting of pickling cucumbers in some areas is generally because the yields do not compare favorably with those obtained by repeated hand harvests. In most areas, however, the cost of labor is making hand harvesting of pickling cucumbers prohibitive. The newer gynoecious cultivars that provide uniform fruit set and maturity with good fruit size are producing better once-over harvest yields. Also, improvements in mechanical harvesters have increased field recovery and decreased damaged fruits. It appears that mechanical harvesting will one day replace hand harvesting for all pickling cucumbers.
For hand-harvested fresh market slicers and pickling cucumbers, fruits are harvested when they have reached the desired market size. For pickling cucumbers, this will be at a very immature fruiting stage. Generally, pickling fruits are picked 5-12 days after anthesis (flowers fully open). In warm weather, this may mean a harvest as soon as 32-36 days after planting. By 10-12 days after antheses, fruits may exceed marketable size (2 inches), especially if temperatures are warm. Fresh market slicers take longer to reach the desired size, and harvest may begin 50 days after planting for some gynoecious hybrids and more than 65 days for monoecious cultivars.
For destructive machine-harvested plantings, a compromise must be made between fruit size and total yields. This is usually decided by the processor. The growers must coordinate harvest time with the processor's capability to handle the crop at the plant.
For multiple harvests, the frequency of picking will depend on the size desired and the weather conditions. Cucumber fruits mature very quickly, especially in warm weather, when they can have a 40% increase in weight in 24 hours. Fruits should not be left on the vine, since oversized fruits will tend to inhibit new fruits to set. Fresh market slicers in the field are generally harvested every 2-3 days. When they are hand-harvested, the growing season in the field may last 100-120 days or more. Slicers grown in greenhouses may be harvested almost daily. Undersized fruits (less than 0.5 inch) should not be picked. When hand-harvested, fruits should be twisted and snapped off the vine, since pulling results in much vine damage and may uproot the plant.
Grading and sorting of fruit can be done in the field or packing shed. Slicing cucumbers are graded by fruit diameter, length, shape, and color. The fruit should be firm, straight, uniformly smooth, and deep green. The desired length is 6.0-8.5 inches, with a diameter of 1.5-2.5 inches. Standard grades include "U.S. Fancy," "U.S. Extra No. 1," " U.S. No. 1," "U.S. No. 1 Large," "U.S. No. 1 Small," and "U.S. No. 2." Pickling cucumbers are generally graded by fruit diameter into "No. 1" (up to 1.06 inches), "No. 2," (1.06-1.5 inches), and "No. 3" (1.5-2.0 inches). Fruits greater than 2 inches in diameter are called "oversize."
Cucumbers are normally hydrocooled to remove field heat as soon as possible. Fruits ripen rapidly at temperatures above 50F, resulting in color change from green to yellow. They can be held 10-14 days at 50-55F and 95% relative humidity. Fruits are subject to chilling injury if they are held longer than 2 days at temperatures below 50F. Yellowing is accelerated if cucumbers are stored with apples or other crops giving off ethylene. Slicers for fresh market are usually waxed to reduce moisture loss and packed in waterproof cardboard cartons prior to marketing.
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