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Cucumber
Scientific name:
Cucumis sativus
Order/Family:
Violales: Cucurbitaceae
Importance:
medium
Pests and Diseases (clicking takes you to the pest and disease pages):
Virus diseases, Fruit rot, Scab, Epilachna beetles, Flea beetles, Red spider mites
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 Geographical distribution indicated in red
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General Information on CucumberAgronomic AspectsInformation on Major Cucumber DiseasesInformation on Major Cucumber PestsInformation Source Links
Cucumber is a member of the Cucurbitaceae family, which includes pumpkins, squash, gourds and zucchini. Cucumber is grown for the immature fruits, which are eaten fresh (slicing cucumber), or used for pickles (pickling cucumber) . The slicing cucumbers are peeled, sliced and served with vinegar or dressing, or as an ingredient of salads. The large, yellow, round types are boiled and eaten as an ingredient of stews. Pickling cucumbers are preserved or marinated with vinegar, salt, or spices. They can also be used fresh. Cucumbers are a good source of Vitamin C.
Climatic conditions, soil and water management
Cucumber requires a warm climate. The optimum temperature for growth is about 30°C and the optimum night temperature 18-21°C. In the tropics, elevations up to 1700 m appear to be suitable for cucumber cultivation. A lot of light tends to increase the number of staminate (male) flowers. Cucumbers need a fair amount of water but they cannot stand waterlogging. High relative humidity encourages downy mildew. The soil should preferably be fertile and well-drained, with a pH of 6.5-7.5. Long and medium long slicing cucumber varieties are grown in greenhouses where climate and other growing conditions can be controlled. Propagation and planting
Cucumber is propagated by seed. Soil preparation requires generous incorporation of well rotted manure. About 30 t/ha or 15 tons/ha should be applied inside the planting holes together with a spoonful of rock phosphate (3 tea spoons) for each planting hole. Sowing is done directly in the field with several seeds per hill, 90-120 cm apart, then thinned to 2-3 plants per hill, or seeds are sown in nursery beds and seedlings transplanted to the field at the 2-true-leaf stage at 30-40 cm within and 1-2 m between the rows. Sowing rates per ha are about 2.5-3 kg for direct seeding and 1 kg when transplanted. Cucumber cultivated for pickles is planted closer, up to 250,000 plants/ha. For greenhouse varieties plants are started in individual pots and transplanted to permanent position when they have 2-3 permanent leaves. Cucumber varieties are categorised into four types on basis of fruit length:
- Long cucumbers: Fruit length over 30 cm. Examples: Berlin RZ / Bologna RZ / Cumlande RZ / Myrthos RZ / Pluto RZ / Virginia RZ)
- Midi cucumbers: Fruit length between 18 -24 cm Examples: Media RZ
- Mini cucumbers: Fruit length between 15 -19 cm. Examples: Khassib RZ / Gianco RZ
- Cocktail cucumbers: Less than 15 cm. Examples: Rania RZ
Other varieties include:
- Ashley
- Poinsett. Poinsett is a variety with a very high yield potential, good disease and heat resistance.
- Long Fellow
- Hybrid Victory
- Kande (new variety produced in Tanzania)
Because varieties change all the time, please ask your local seed company to give information about the available varieties.
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| © A. Bruntse |
Husbandry
Weed control is necessary until the plants cover the soil entirely. Support (stakes) should be provided for some cultivars, and the tip of the main stem can be nipped off to encourage branching. Irrigate at frequent intervals, and maintain a high level of soil moisture throughout the growing period. Lateral shoots can be pruned after the first fruits have formed to limit leaf and flower production. Greenhouse varieties are staked according to preferred practices, usually by means of twisting the growing stem around a string attached to an overhead strong wire. There are indications that irrigation water containing applications of effective micro-organisms (EM) can prevent damping off and early attacks of diseases on leaves. Irrigation should preferably be applied in the form of drip irrigation in order to prevent water splashes and spread of diseases. Staked cucumbers are very susceptible to wind, so if grown in open land should be carefully protected from wind.Harvesting
Cucumbers for fresh consumption are harvested before they are fully mature, usually starting about 50- 60 days after planting, and thereafter every few days. For pickling, immature fruits of several stages are harvested. Only for seed production are cucumbers allowed to mature on the plant.
Cucumbers should be handled with care as they get damaged easily during transport. Depending on variety one plant may yield up to 10 fruits, and total yields with good plant care can easily reach 50 tons/ ha of the larger fruit types. More common yields are 25-30 tonnes/ha. Fruits should not be left to ripen on the vines as the plants will cease to bear. The marketed fruit must be firm, green and the size typical of the cultivar. Some of the long slicing cultivars of cucumber are packed individually before marketing and cooled.
Virus diseases
Many viruses affect the cucumber family. The important viruses include cucumber mosaic virus, watermelon mosaic virus and squash mosaic virus. Field symptoms of these three diseases are similar and therefore it is very difficult to separate them by symptoms alone. Leaf symptoms include a prominent light and green mosaic pattern, mottling (yellow with green islands or blisters), and in severe cases, leaf distortion whereby affected leaves appear fern-like. Diseased fruits are malformed (slightly to severely misshaped with wart-like lumps).
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| Virus on cucumber |
| © A. A. Seif |
It is not seed transmitted except through seed of perennial wild cucumber (Echinocytis lobata) and chickweed (Stellaria media). It is mechanically transmitted and in nature it is spread by various species of aphids. It has a very extensive host range including such varied species as bananas, carrots, cowpeas, lupine, lilies, onions, passion fruit, potatoes and tomatoes.
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| Mosaic virus on watermelon |
| © A. M. Varela, icipe |
This virus is mechanically transmitted and also spread by several species of aphids. It is not seed transmitted. Its host range is primarily restricted to cucurbits although one of its strains infects peas.
Squash mosaic virus
It is mechanically transmitted. It is transmitted through seeds of melons and squash. It is also transmitted by spotted, striped and banded cucumber beetles, which attack cucumbers in the Americas. The Epilachna beetle (Epilachna chrysomelina) a pest of cucumber in Africa, is also vector of squash mosaic virus. Its host range includes cucurbits, peas, coriander, and salad chervil.
What to do:
- Use tolerant / resistant varieties if available
- Remove infected plants (disinfect hands and tools with 70% alcohol after contact with infected plants)
- Do proper weeding
- Control insect vectors. A sustainable approach of controlling aphids is important to prevent aphids reaching the crops and transmitting virus.
- In case of squash mosaic virus use disease-free seeds
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| Downy mildew on cucumber |
| © Jürgen Kranz, Courtesy of EcoPort |
Symptoms on leaves appear as small, pale-yellow areas on upper leaf surface. Under humid conditions, a purplish, grey whitish growth may be seen on the underside of the yellowish spots. Affected leaves curl, shrivel and die. Most downy mildew fungi require cool weather for reproduction and development. This is not true of the cucurbit downy mildew fungus. Optimum temperature for infection is at 16 to 22º C. It can survive when temperatures are over 37.8º C. The most critical factor for infection is a film of moisture and / or long dew periods on leaves. Disease spread is primarily thorough by wind and rain splash. The fungus attacks only members of the cucumber family, mostly those that are cultivated, although it can infect wild cucumber and a few other weed hosts.
What to do:
- Use resistant varieties, if available
- Leave wide spacing between plants
- Avoid overlap cucumber plantings
- Copper fungicides at 0.1% can provide control
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| Severe powdery mildew attack (Sphaerotheca fuligenea) on cucumber |
| © Jürgen Kranz Courtesy of EcoPort |
Symptoms first develop as a whitish talcum-like powdery growth on lower leaf surface. The powdery growth is composed of fungal spore mass. These areas covered by white powdery growth may enlarge and join up to cover both lower and upper leaf surfaces. Severely affected leaves dry, turn brown and become brittle. Vines can be also attacked. Secondary effects of the disease include sun-burning and premature ripening of fruits.
Powdery mildew affects cucumber, gourd, muskmelon, pumpkin, squash and watermelon. Other hosts include African violets and pawpaws. The powdery mildew fungi are influenced by plant age, humidity and temperature. Foliage is most susceptible 16 to 23 days after unfolding. The fungi reproduce under dry conditions. Infection increases as humidity increases, but does not occur when leaf surface is wet. Optimum temperature for infection is about 27.4º C. However, infection can take place at a temperature as high as 32º C and relative humidity as low as 46%.
What to do:
- Use resistant varieties, if available
- Spray with sulphur based fungicides, which provide good control
- Destroy weeds belonging to the cucurbit family
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| Angular leaf spot on cucumber |
| © A. A. Seif |
Spots on leaves angular in shape and variable in size due to leaf veins that limit their enlargement. Initially, spots are water-soaked. In moist weather, bacteria ooze from the spots in tear-like droplets, which dry making the tissue white. Affected leaf dries and shrinks, and it may tear away from the healthy portion leaving irregular holes. Leaves approaching maturity are more susceptible than older leaves. Fruits may also be attacked. Fruit spots are small, nearly circular and superficial. The bacteria survive in association with seed. When infected cucumbers are used for seed extraction, the seed can be contaminated during fermentation process.
The bacteria can also survive in soil or infected crop debris. Drainage water can spread the bacteria in the soil. Angular leaf spot disease is favoured by wet conditions, frequently associated with rainfall and overhead irrigation. Optimum temperature for disease development is 23.9 to 27.8º C. The disease attacks gherkin, muskmelon, pumpkin, squash, vegetable marrow and watermelon.
What to do:
- Use resistant varieties, if available
- Use disease-free seed
- Practice crop rotation. A crop rotation of 1 to 2 years is recommended
- Avoid run-off water from nearby cucurbit fields and overhead irrigation
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| (Colletotrichum orbiculare) damage to pumpkin leaf (Cucumis sativus). |
| © Clemson University - USDA Cooperative Extension Slide Series, www.insectimages.org |
The fungus can attack all the above-ground plant parts. Cotyledons (seed leaves) of affected seedlings droop and wilt. Lesions (elongated spots) may form on stems of affected seedlings near the ground. Spots on leaves start as small yellowish areas that enlarge and turn brown. The affected tissue dries, breaks and the whole leaf dies. On vines, the spots are elongated and may kill the vines.
Symptoms are most noticeable on fruits. Spots on fruits are circular, black, and sunken. When wet, the centres of the spots become salmon coloured due to a mass of fungal spores. Affected fruits can be destroyed by secondary soft-rot organisms, which enter through broken rind. The fungus is seed-borne. It can survive in crop debris and in weeds belonging to the cucurbit family. Fungal development is promoted by wet conditions, high relative humidity and moderate temperatures (20 to 23.9º C). Its host range includes cucumber, gherkin, gourd, muskmelon, and watermelon. Cucurbit weeds can also be attacked.
What to do:
- Use resistant varieties, if available
- Use disease-free seeds
- Practice crop rotation
- Destroy volunteer cucurbits and weeds
Fusarium wilt (Fusarium oxysporium f.sp. cucumerinum)
In seedlings, the cotyledons lose their healthy look (luster) and wilt. This is followed by complete collapse of the plants. Older plants initially exhibit wilting and yellowing of leaves near the crown. Later individual vines and then the whole plant wilt and dies. If the taproot and stem are split open, an orange-brown discolouration of the water conducting tissues will be seen. Fruits from affected vines are small with poor flavour and colour.
The fungus is a soil inhabitant. It enters the roots and grows in the water conducting tissues thereby blocking water movement. The fungus is also carried on the seeds and in soil adhering to farm implements. It can persist in soil for long periods. The disease is favoured by warm weather (optimum soil temperature for infection is about 27.8º C) and air humidity of more than 80% over a long period.
What to do:
- Use resistant varieties, if available
- Use disease-free seeds
- Avoid spread of the fungus through contaminated farm implements and furrow irrigated water
Fruit rots
Fruit rots are of minor importance in Africa; they are primarily post-harvest problems during storage. In most African countries, cucumbers are sold fresh from farm, consumed and are hardly stored for long (exception could be supermarkets in urban areas where fruits are kept on shelves).
What to do:
- Avoid injuries during harvesting
- Store fruits properly after harvest
Scab (Cladosporium cucumerinum)
It attacks all aboveground plant parts. Initial symptoms on leaves appear as light water-soaked or pale green spots. The spots are numerous and can appear on and between veins. Elongate spots may develop on petioles and stems. The spots later turn grey to white and become angular. The fine veinlets in the spots may be brown and are distinct against a white background. Dead leaf tissue cracks and breaks away until the whole leaf is ragged. Fruits can be attacked at all stages of growth. However, young fruits are most susceptible. Plant tissue near the spots may produce sap, initially watery but later becomes gummy to hard.
The fruit spots are cankerous and with time become darker, sunken until a pronounced cavity is formed. Under moist weather, a dark-green velvety layer of fungal growth appears on the cavities. The fungus survives in crop debris, soil and on seed. It is spread by insects, farm tools and wind. The disease is most severe at 100% relative humidity and at relatively cool temperatures (21-25ºC). Its host range includes cantaloupe, gherkin, muskmelon, pumpkin, squash and watermelon.
What to do:
- Use resistant varieties,if available
- Use disease-free seeds
- Practice crop rotation with nonrelated crops
Aphids (Aphis gossypii)
The cotton aphid (Aphis gossypii) is common on cucurbits, including cucumber. Colonies of green to blackish aphids are found on tender shoots, mainly on the lower leaf surface, where they suck sap. The growth of the attacked shoots is stunted and the leaves are curled and twisted. Aphids excrete honeydew, which leads to growth of sooty mould, and may attract fruit flies. Aphids, in particular winged aphids, transmit virus diseases (e.g. cucumber mosaic virus) when moving from plant to plant.
What to do:
A sustainable approach of controlling aphids include among others:
- Plant barrier crops
- Apply sticky traps
- Use botanicals (e.g. neem extracts)
- Covering the ground with an aphid deterrent material like aluminium foil boards.
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| Fruit flies in watermelon fruit |
| © A. M. Varela, icipe |
These are important pests of cucumber and other cucurbits. Fruit flies pierce the fruits and lay eggs in fruits. The fruit fly maggots feed inside the fruit causing sunken, discoloured patches, distortions and open cracks. These cracks serve as entry points for fungi and bacteria, causing fruit rot.
What to do:
- Avoid continuous cultivation of cucumbers at the same place since this may lead to fruit fly outbreaks.
- Destroy all infested fruit
- In small plots, wrap individual fruits or bag them with newspaper or paper bags to prevent fruit flies from laying eggs fruits. Wrapping or bagging should be started shortly after fruit set.
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| Whiteflies under leaf. Adult whiteflies are about 1mm long. |
| © Clemson University, Department of Entomology |
They suck plant sap and excrete honeydew where moulds grow, which may affect plant growth and vigour. The tobacco whitefly is considered a major pest due to its ability to vector various virus diseases, which cause considerable damage to cucurbits.
What to do:
- Conserve natural enemies. Parasitic wasps are important in natural control of whiteflies
- Use reflective mulches (see aphids). Reflective mulch repels whitefly adults in pumpkin, cucumber and zucchini squash, resulting in delayed and reduced attack by this pest with consequent reduction in damage as shown in experiments in USA. Whitefly density on pumpkins and cucumbers plants growing over reflective mulch was reduced 10- to 14-fold as compared to plants growing on bare soil. This was reflected in significantly higher yields in plants grown over reflective mulch than in those grown over unmulched soil. (UCANR, 2003; Summers & Stapleton 2002)
- Whenever necessary spray crop with neem products. Neem-based pesticides are reported to inhibit growth and development of immature stages, and to reduce egg laying by adult whiteflies
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| Larvae of Epilachna beetle and damage caused on water melon |
| © A. M. Varela, icipe |
Adults of this beetle, also known as the African melon ladybird, are 6-8 mm long, reddish in colour with a number of black spots on the wing cases. The larvae are 7-9 mm in length, soft and covered with dark coloured spines. Adults and larvae feed on leaves leaving a fine net of veins. Damaged leaves shrivel and dry up. Young plants can be entirely destroyed. Older plants can tolerate considerable leaf damage. This beetle is a vector of squash mosaic virus. Epilachna beetles attack all cucurbits.
What to do:
- Spray neem extracts. Simple neem-based pesticides have given control of this pest in Togo. Thus, feeding by Epilachna beetles in squash and cucumber could be reduced significantly by weekly applications of aqueous neem kernel extracts at concentrations of 25, 50 and 100 g/l and neem oil applied with an ultra-low-volume (ULV) sprayer at 10 and 20 l/ha (Ostermann and Dreyer, 1995).
Flea beetles (Podagrica spp)
They are tiny to small (1.5 to 3 mm) long leaf beetles with well-developed hind legs. They are named for their habit of jumping like fleas when they are disturbed. The colour of the adult beetles varies from black, brown, black and yellow striped or metallic blue-green depending on the species. Adult flea beetles chew small round holes (shot holes) in leaves, giving them a sieve like appearance. On rare occasions, they may feed directly on ripe fruit, just below the calyx. This damage is usually seen only in plants that show extreme foliar stress resulting from lack of water or powdery mildew. The larvae of flea beetles live in the soil and feed on roots, but the damage caused is not of economic importance. Adult flea beetles can be particularly damaging to young plants. Seedlings are most vulnerable to flea beetle feeding when stressed, particularly by inadequate moisture. Older plants can withstand considerable leaf perforation.
What to do:
- Monitor the crop frequently, particularly during the first stages of the crop. Even a small flea beetle population can cause significant damage to a crop in the cotyledon or first-leaf stages
- Provide good nutrition and favourable growing conditions. This helps to avoid plant stress from diseases and moisture, and helps plants survive flea-beetle attack.
- Weed in and around fields. This may help to eliminate flea beetle shelter and breeding grounds, reducing crop damage.
- Keep plant diversity in the farm. Living mulches or polycultures are known to reduce flea-beetle damage. Diversity in the farm support populations of natural enemies.
- When necessary spray botanicals or other alternative products. Extracts of neem, rotenone, pyrethrin, sabadilla, garlic, onion and mint alone or in combination have been recommended for control of flea beetles. Insecticidal soap is reported to give partial control of flea beetles. However, sprays combining rotenone with insecticidal soap are considered very effective. Diatomaceous earth and rock powders have been observed to reduce flea-beetle populations but applications must be renewed regularly after rainfalls.
Red spider mites (Tetranychus spp.)
They attack leaves of cucumber. Attacked leaves have a stippled appearance, turn yellowish to whitish and dry up. Often young plants are entirely destroyed. In older plants growth can be severely stunted and the fruit set considerable reduced. Spider mites can be a problem in dry and hot conditions. Plants under water stress (drought) are more likely to suffer damage by spider mite.
What to do:
- Conserve natural enemies. Predatory mites and anthocorid bugs are important in natural control of mites
- Avoid use of broad-spectrum pesticides. They may kill natural enemies and may lead to mite outbreaks
- Provide good growing conditions for plants. Healthy plants are more likely to withstand mite attack. Adequate irrigation is particularly important. Apply mulch and incorporate organic matter into the soil to improve the water holding capacity and reduce evaporation
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| Root-knot nematodes. Field symptoms are typically of stunted, poorly growing plants with yellowing leaves. Infected root systems show characteristic knots or galls. |
| © H.J. Jensen (Reproduced from CABI 2006) |
Symptoms of infestation by root-knot nematodes are similar in all crops: wilting of plants and if infested plants are pulled from the soil the roots can be seen to be distorted, swollen and bearing knots. The infested roots eventually rot and affected plants die.
What to do:
- Use resistant varieties, if available
- Practice mixed cropping. Mixed cropping with African marigold (Tagetes spp.) minimise root-knot nematode damage. Intercrop with different mustards (e.g. Brassica juncea var. integrifolia or Brassica juncea var. juncea) on infested fields. As soon as mustards are flowering they are mulched and incorporated into the soil. While incorporated plant parts are decomposing in a moist soil, nematicidal compounds of this decomposing process kill nematodes. Two weeks after incorporating plant material into the soil a new crop can be planted or sown (phytotoxic effects are usual if the crop is planted before two weeks).
- Maintain high levels of organic matter in the soil (manure or compost)
- Use biofumigation where possible (biofumigation involves incorporation into the soil of crop residues of crucifers, resulting in high levels of organic matter).
- Use neem extracts
- AIC, Nairobi (2003). Fruits and Vegetables Technical Handbook
- AVRDC International Cooperators' Factsheet on Cucurbits www.avrdc.org/LC/cucurbits/publications.html
- Beije, C.M., Kanyangia, S.T., Muriuki, S.J.N., Otieno, E.A., Seif, A.A., Whittle, A.M. (1984). Horticultural Crops Protection Handbook.National Horticultural Research Station, Thika KEN/75/028 and KEN/80/017/
- Blay, E., Cudjoe, A. R., Braun, M. (editors) (2000). Handbook of crop protection recommendations in Ghana: An IPM approach. Vol 2; vegetables. Plant Protection & Regulatory Services Directorate (PPRSD) and the Integrated Crop Protection Project, German Development Cooperation (GTZ).
- Bohlen, E. (1973). Crop pest in Tanzania and their control. Federal Agency for Economic Cooperation (BFE). Veralgh Paul Parey. ISBN 3-489-64826-9.
- CAB International (2005). Crop Protection Compendium, 2005 edition. Wallingford, UK www.cabi.org
- Ekesi, S., Billah, M.K. (Eds) (2006). A field guide to the management of economically important tephritid fruit flies in Africa. ICIPE. ISBN: 92-9064-179-7.
- Kuepper, G. (2003). Flea Beetle: Organic Control Options. NCAT Agriculture Specialist. Published ATTRA Publication #CT114. National Sustainable Agriculture Information Service.
- Ministry of Agriculture and Rural Development (Kenya) (MoARD) & Japan International Cooperation Agency (JICA) (2000). Local and Export Vegetables Growing Manual. Reprinted by Agricultural Information Resource Centre, Nairobi, Kenya. 274 pp.
- Ostermann, H., Dreyer, M. (1995). Vegetables and grain legumes. In ?The Neem tree Azadirachta indica A. Juss. and other meliaceous plants sources of unique natural products for integrated pest management, industry and other purposes?. Edited by H. Schmutterer in collaboration with K. R. S. Ascher, M. B. Isman, M. Jacobson, C. M. Ketkar, W. Kraus, H. Rembolt, and R.C. Saxena. VCH. pp. 392-403. ISBN: 3-527-30054-6
- Sherf, A.F., Macnab, A.A.(1986). Vegetable Diseases and Their Control. 2nd. Edition. John Wiley & Sons Inc. USA. ISBN: 0-471-05860-2
- Summers, C.G. and Stapleton, J. J. (2002). Use of UV reflective mulch to delay the colonization and reduce the severity of Bemisia argentifolii (Homoptera: Aleyrodidae) infestations in cucurbits. Crop Protection. Volume 21. Pages 921-928. www.sciencedirect.com
- UCANR. UC helps pumpkin farmers produce pumpkins without pesticides. October 2003. www.ucanr.org
