CUCUMBER INTRODUCTION

The cucumber belongs to the Cucurbitaceae (gourd family). The cucumber belongs to the genus Cucumis of which there are 20 to 25 species found mostly in Asia and Africa. Only two Cucumis sativus (cucumber) and Cucumis melo (melon, muskmelon and persian melon) are of commercial importance in North America. It is an annual trailing or climbing vine usually with flowers of both sexes on the same plant(monoecious). Current market hybrids are produced on genetically gynoecious lines(all female blooms). Commercial seed lots have up to 10% of a monecious variety to provide sufficient pollen for fruit set. European greenhouse cucumbers set fruit without pollination (parthenocarpic). The cucumber is native to the northwest of India and has been cultivated there for at least 3000 years. The cucumber was known in France in the 9th century and was common in England in 1327.

          Cucumbers are very sensitive to cold temperatures and may be killed at 1°C. It has a minimum germination temperature of 16°C, an optimum germination range of 16°C to 35°C, with an optimum germination temperature of 35°C, and a maximum germination temperature of 40°C. Soil temperatures at planting must be at least 10°C for table cultivars and 13°C for gherkin cultivars. Planting must be delayed until all danger of frost is past. Windbreaks are essential for early production of this crop.

          A well drained loam to sandy loam soil with high organic matter with no frost pockets or problems with surface drainage is the ideal field situation. Wind protection, natural or artificial, is necessary.

           Slicing cucumbers, with the aid of plastics, are harvested from the field in early to mid July. Most of the field crop does not come on until early August. Slicing cucumbers average 15,000 kg per hectare with some yields as high as 22,000 kg per hectare. Due to market gluts in warm seasons not all of the crop is marketed. (2,500 doz per hectare to 5,000 doz per hectare). Pickling cucumber yields depend on the size of fruit harvested. (15,000 to 17,000 kg per hectare).

          Cucumbers are an important crop in the Atlantic area though market potentials may not be large. On the fresh side there is a strong demand for the product as it is a salad vegetable but processing cucumber markets have declined. The greatest potential would seem to be to extend the season by earlier production (use of plastics) and to look for speciality markets.

           Nutrient Content: Contains fair amounts of potassium, calcium and folate; and small amounts   of other nutrients including Vitamin C. Very low in calories. 6 slices contains 5 kilocalories.

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 cproduction 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 brittleand 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.