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Cucumber - Diseases, Pests and Problems

Basic Information

Problem: Flea Beetles
Affected Area: Leaf

Description: Small 1/16 ? brown jumping beetle. Makes tiny holes in leaves causing them to develop a shot-hole? appearance.

Control: Do not generally do serious damage. Dust with Rotenone, Remove debris each year. Rotate location

Problem: Aphids
Affected Area: Leaf and Stem

Description: Small Insects found on new stems and the underside of the leaf. Usually green. They suck fluids from the plant leaving a honey dew substance behind. Leaves turn pale yellow.

Control: Insecticidal soaps or a strong stream of water. Diazinon, sevin, and thiodan are also registered for aphids on cucumbers. * Pesticide use and recommendations for various areas are constantly changing. Check with your County agent for current recommendations.

Problem: Slugs and Snails
Affected Area: Entire plant

Description: Large portions of young plants missing.

Control: Slugs and snails are very susceptible to desiccation (drying) and require a moist, shady place to live. Cultural practices which promote a sunny, dry environment will discourage them. Avoid too-frequent waterings allowing soil surface to dry out between irrigations. Keep garden free of debris, boards, bricks, and stones where they hide. Hand picking these pests is very effective. Create ?traps? for hand picking by laying boards in the garden. Slugs and snails will congregate under them. Lift the boards each morning and collect the slugs and snails. Dispose of them completely as they will crawl back if tossed out of the garden and eggs inside dead pests can still hatch to produce more of these pests. Slug and snail bait containing metaldehyde can be placed near food plants as long as they do not contact edible portions of the crop. Most effective when moistened, but not water logged. Snail bait attracts slugs and snails from several feet away so bait stations are effective. Stations help protect birds, pets and other non-target animals which are also attracted to the bait. Place small piles of bit under a slightly propped up board or use container such as a cottage cheese or yogurt carton. Bury carton to the mouth of the container. Place small amount of commercial bait inside and moisten with apple juice, orange juice or water. Cut hole in lid to allow access and place lid on container. Containers may also hold beer or yeast water to attract slugs and snails in where they drown. Place bait stations wherever slugs and snails are active or around perimeter of garden.

Problem: Cucumber Beetle
Affected Area: Leaf, Stem, and Root

Description: Western Spotted Cucumber Beetle and Western Striped Cucumber Beetle are the two most common to attack vine crops in the West. Adults are about 1/4 inch long with black heads, yellow thorax and yellow wing covers. Spotted species are greenish yellow, with 12 black spots on their back. Striped are pale orange-yellow with three longitudinal black strips on their backs. Both winter over as adults and deposit eggs in the soil. ? Larvae bore into roots and stems below soil line. Adults chew leaves. May spread wilt and mosaic diseases.

Control: Pick by hand, spray with hose (both sides of leaves) but this will not kill. Dust with rotenone or apply diazinon. * Pesticide use and recommendations for various areas are constantly changing. Check with your County agent for current recommendations.

Problem: Damping-off
Affected Area: Seedling

Description: Young seedlings wilt and die.

Control: Use treated seed and let soil dry out between waterings.

Problem: Cucumber mosaic
Affected Area: Leaf, Stem, and Fruit

Description: Vines are stunted, new leaves are dwarfed, mottled, distorted and may wilt and die. Fruit distorts and yellows early.

Control: Plant resistant varieties. Control aphids and cucumber beetles. Rotate placement from year to year.

Problem: Powdery mildew
Affected Area: Leaf

Description: White powdery substance on the leaves. Spores are transmitted by wind to healthy plants.

Control: Use surface or underground watering method to avoid wetting leaves. Plant resistant varieties. Change location from year to year. Fungicidal sprays are only moderately effective.

Problem: Alternaria Leaf Spot
Affected Area: Leaf

Description: Dry flecks surrounded by yellow halos appear on the leaves and enlarge into spots, which may group together to form nearly circular lesions. The lesions bear the black brown conidia of the pathogen. Severely infected leaves become yellow and senescent and then die.

Control: Satisfactory control can be achieved by reducing relative humidity in greenhouses, removing infected plant debris prior to crop establishment, and applying protectant fungicides.

Problem: Anthracnose
Affected Area: Leaf, Petiole, Stem, and Fruit

Description: On cucumber leaves, lesions usually first appear near veins, are roughly circular, range from light brown to reddish, and can reach more than 1 cm in diameter. The leaves may be distorted, and the centers of lesions may crack or drop out, creating a shot-hole appearance. On petioles and stems, lesions are shallow, elongated, tan areas. On fruit, lesions are circular, sunken, water-soaked areas which first develop as the fruit.

Control: Chemical control and resistant cultivars are the most effective controls of the disease.

Problem: Aphids
Affected Area: Leaf

Description: Aphids damage cucurbits by direct feeding, by contamination with excrement, and as vectors of plant pathogens and can occur just after the formation of the first true leaf.

Control: Insecticides are not effective in preventing the spread of aphid borne viruses, but may be helpful in control the onset of infection. Refer to current recommendations for registered insecticides.

Problem: Aster Yellows
Affected Area: Leaf, Flower, and Fruit

Description: Infected plants are easily detected by the conspicuous yellowing of young leaves, the proliferation of secondary shoots, and the rigid, erect habit of the plants. Leaves are often misshapen and smaller than normal and have stiff, thick laminae. Flowers are usually malformed and greenish yellow and often have prominent leafy bracts. Fruits are small, malformed, and lighter than normal color.

Control: Application of insecticide can drastically reduce leafhopper populations but is often ineffective in reducing the disease.

Problem: Bacterial Brown Spot
Affected Area: Fruit

Description: In honeydew melons, symptoms appear as conspicuous yellow brown, smooth, firm lesions up to 40 mm in diameter. Symptoms on melon are very similar with firm lesions that are slightly yellow brown, and up to 10 mm in diameter, extending 1-2 mm below the epidermis. Symptoms on melon fruit are obscured by the net.

Control: No control measures have been developed.

Problem: Bacterial Soft Rot
Affected Area: Fruit

Description: Early symptoms of bacterial soft rot are a distinct water-soaked appearance and pronounced softening of the surrounding tissue. As the decay progresses, the fruit tissue becomes extremely soft and mushy and often collapses, losing its original form.

Control: Avoiding bruising and injury to the fruit is the first step in controlling bacterial soft rot.

Problem: Bacterial wilt
Affected Area: Runner and Leaf

Description: Individual runners or whole plants wilt and die rapidly. Affected runners appear dark green at first and then dry out as the wilt becomes irreversible. Plants may wilt dramatically during the heat of the day but partially recover by morning. Foliage of affected plants often appears yellow.

Control: Control of bacterial wilt depends on control of the cucumber beetle vectors. Roguing wilted plants, using trap crops, and implementing appropriate insecticide programs are the best forms of control.

Problem: Belly Rot
Affected Area: Flower

Description: On the undersides and blossom ends of cucumber fruit, the disease produces water-soaked, tan to brown lesions, which become sunken, cratered, irregular, and dried as they enlarge.

Control: Soil may be fumigated before planting. In humid areas, artificial barriers can be placed between the soil and the fruit to prevent infection. Another effective method of avoiding the pathogen is deep plowing before planting.

Problem: Black Rot
Affected Area: Fruit

Description: In cucumber, fruit rot can develop before harvest, but it usually develops during transit or storage. Before harvest, a black decay occurs, especially at the blossom end, and can extend into the pulp. On watermelon, distinct, circular, greenish tan to black spots first appear on any part of the fruit. The lesions later have black centers, and under moist conditions many pycnidia and perithecia develop near their centers. In squash, if fruit are damaged prior to or during storage, a brown to pinkish water-soaked area develops, followed by blackened areas with conspicuous fruiting bodies.

Control: Special care should be exercised to avoid rind injuries to all fruit, especially winter squash and pumpkins, as wounds provide entry for the black rot organism in storage.

Problem: Blossom-End Rot
Affected Area: Flower and Fruit

Description: Symptoms first appear as small, light brown spots at the blossom end of immature fruit. As affected watermelons grow, these spots can enlarge rapidly to form dark, sunken, leathery lesions. The lesions are generally dry and can be as large as the diameter of the fruit. A soft, secondary wet rot may develop if affected areas of the fruit are invaded by decay fungi or bacteria.

Control: NA

Problem: Blue Mold
Affected Area: Fruit

Description: In general, cucurbit fruits with blue mold have been predisposed by temperature, bruising, and injury, and they typically have other problems.

Control: Blue mold can be effectively prevented by eliminating predisposing conditions, maintaining low temperatures in storage, and moving the produce within its reasonable postharvest shelf life.

Problem: Choanephora Fruit Rot
Affected Area: Flower and Fruit

Description: The disease affects both blossoms and fruit. When flowers are invaded early, they turn soft and usually drop off the plant. Later infections cause the flowers to turn brown, and if the fruit has begun to develop, the fungal mycelium invades the fruit tissue, causing it to decay in a wet rot.

Control: No practical control measures have been developed.

Problem: Crater rot
Affected Area: Leaf and Fruit

Description: The disease is characterized by shallow to deep, sunken lesions, 2-50 mm in diameter. Large lesions often penetrate to the seed cavity in melon and honeydew. Lesions on leaves are round to irregular in shape, 2-15 mm in diameter, with a tan center, brown margins, and a yellow halo, and they often form concentric rings. Abundant greenish black sporodochia may also be arranged in concentric rings on either surface of the leaf.

Control: Foliar diseases can be controlled with fungicides.

Problem: Cucumber Mosaic
Affected Area: Leaf, Flower, Stem, and Growth

Description: In cucumber, melon, and squash, cucumber mosaic virus causes severe plant stunting, prominent foliar yellow mosaic, malformation, prominent downward leaf curling, and drastic reduction of leaf size and stem internodes. Flowers of severely affected plants may have prominent abnormalities and greenish petals.

Control: The best forms of control include using resistant cultivars, insecticides, reflective mulches, and mineral oils.

Problem: Phytophthora blight
Affected Area: Root

Description: Mature plants show symptoms of root and crown rot. Initially, feeder roots are depleted and soon after, brown lesions develop on lateral roots. Sudden wilt is another symptom when healthy-appearing plants suddenly collapse during the heat of the day.

Control: Control of root rot can be achieved by planting on raised beds to allow for maximum water drainage after each irrigation.

Problem: Downy Mildew
Affected Area: Leaf

Description: Symptoms of downy mildew are first evident as small, slightly yellow to bright yellow areas on the upper leaf surface with the color less vivid on the corresponding lower leaf surface. Lesions appear first on the older crown leaves and appear progressively on the younger, more distal leaves as these leaves expand. As the lesions expand, they may remain yellow or become dry and brown. Lesion margins are irregular on most cucurbits, but on cucumber they are angular and bound by leaf veins.

Control: The best forms of control include using resistant cultivars, applying fungicides, and using good cultural practices.

Problem: Fusarium Rot
Affected Area: Fruit

Description: The disease can penetrate in a number of ways including, the epidermis, the stem end, and lesions on the surface. It is one of the more common preharvest and postharvest diseases of cucurbit fruits.

Control: Avoid wounding the fruit during harvest and packing, proper storage and transit temperatures, and prompt handling of melons upon arrival at the market provide some protection against postharvest decay.

Problem: Gummy Stem Blight
Affected Area: Leaf and Stem

Description: Circular, tan to dark brown spots appear on the leaves, often first at the margins, and enlarge rapidly until the entire leaf is blighted. Circular, black or tan spots appear on the cotyledons and stems of young plants.

Control: Satisfactory chemical control may be obtained by regular applications of protectant fungicides.

Problem: Lasiodiplodia
Affected Area: Root and Fruit

Description: The disease causes a root rot, and a vine decline in melon at the stem end. Infected tissue is somewhat soft and has a water-soaked appearance. As the disease progresses, the affected tissue becomes brown and shriveled. In the latter stages of decay, the shriveling becomes more pronounced, and black pycnidia and dark gray mycelium develop internally.

Control: Fungicide pastes applied to cut peduncles have been successful in controlling the disease. Care should be taken to reduce injury in the harvesting, handling, and packing of the fruit.

Problem: Leafminers
Affected Area: Leaf

Description: Adult leafminers are small flies that are black and yellow. Adult females puncture the upper surfaces of leaves for feeding and egg laying. Eggs are cream-colored and oval, laid singly in separate leaf punctures.

Control: Scouting should be initiated prior to bloom in all crops, and treatments should be initiated when numerous leaf punctures or small holes are observed on the majority of leaves on the plant.

Problem: Lettuce Infectious Yellows
Affected Area: Leaf

Description: In cucurbits, the characteristic symptom is pronounced interveinal yellowing and leaf curling, and in melons and cucumbers the striking yellow color is accompanied by a green mosaic. Symptoms develop primarily on older leaves.

Control: Allowing a host-free period and stringent weed control is the best control method.

Problem: Mites
Affected Area: Leaf

Description: Spider mites damage cucurbits by puncturing cells of the leaves, mainly on the lower surface. They extract plant juices and chlorophyll, interrupting the normal production of photosynthate. An early sign of infestation is stippled areas on foliage. As feeding progresses, leaves become yellow.

Control: Use recommended insecticides for control.

Problem: Papaya Ringspot
Affected Area: Leaf and Growth

Description: Most susceptible cucurbit species respond to infection with very prominent foliar symptoms and severe plant stunting. Foliage of infected plants often exhibits green mosaic, malformation, puckering, blisters, distortion, and narrow laminae.

Control: Where available, the use of resistant cultivars is the most effective control.

Problem: Pickleworm
Affected Area: Fruit and Stem

Description: Primary damage is due to burrowing within fruits, which renders them unfit for consumption. Often, the only outward sign on an infested fruit is a small entrance hole. In heavy infestations, larvae may burrow into stems and kill plants.

Control: Chemical treatments are the best form of control, but must start when eggs or small larvae are first noticed.

Problem: Pink root
Affected Area: Root

Description: Pink root of cucurbits is characterized by pink to red lesions on secondary and tertiary roots. The disease causes no aboveground symptoms in melon and watermelon plants.

Control: There are no control measures available for the disease.

Problem: Powdery Mildew
Affected Area: Leaf, Petioles, and Stem

Description: Whitish, talcum-like, powdery fungal growth develops on both leaf surfaces and on petioles and stems. Symptoms usually develop first on older leaves, on shaded lower leaves, and on abaxial leaf surfaces. Older, fruit-bearing plants are affected first. Infected leaves usually wither and die, and plants senesce prematurely.

Control: Resistant cultivars and fungicides on the undersides of the leaves and the lower canopy are used to manage powdery mildew.

Problem: Red Rot
Affected Area: Fruit

Description: Symptoms of red rot include a bright red discoloration of the rind with no aerial mycelium or fruiting bodies. The texture of the decayed area is similar to that of healthy tissue. Decayed and healthy tissue are not easily separated.

Control: The growth of the fungus is greatly retarded at 5(C making proper storage temperatures an important role in controlling the disease.

Problem: Rhizopus Soft Rot
Affected Area: Fruit

Description: The initial symptoms of Rhizopus soft rot of cucurbits are a water-soaked appearance and softening of the tissue. As fruits become completely colonized, they often collapse from the weight of other fruit. The diseased tissue is wet, soft, and somewhat pliable, and large portions of it can be removed intact. Internally, the diseased tissue in most cucurbits is characteristically water-soaked and darker than the surrounding healthy tissue.

Control: Rhizopus soft rot can be controlled most effectively by minimizing injury and bruising of the fruit and by proper cooling and temperature maintenance during shipping and storage.

Problem: Scab
Affected Area: Leaf, Runners, and Fruit

Description: On leaves and runners, pale green, water-soaked areas are the initial symptoms. These spots gradually turn gray to white and may become "shot-holed" in appearance. A yellow halo appears around the lesion. Scab can produce the greatest damage on fruit. Spots first appear as small, sunken areas similar to insect stings. A sticky substance may ooze from the infected area, especially on fleshy fruit.

Control: Using resistant cultivars, rotating the crops, and using protectant fungicides are recommended measures for control.

Problem: Sclerotinia Rot
Affected Area: Tendrils, Petioles, and Flowers

Description: Infection tends to occur in dead tendrils and petioles or through withered flowers still attached to developing fruit. The disease is favored by low temperatures and extended wet periods.

Control: Because the disease is relatively minor in cucurbits, no control procedures have been developed.

Problem: Squash Bug
Affected Area: NA

Description: Damage results from the withdrawal of plant fluids. Moderate feeding by a single adult can result in rapid death of seedlings and death in older plants may result from heavy feeding.

Control: Prior to the advent of modern pesticides, hand picking of squash bugs and clean culture were suggested as the best methods of control. In small plantings with only moderate populations of squash bugs, these methods are efficient and cost-effective. In large plantings, often the only alternative for control is the application of insecticides.

Problem: Squash Mosaic
Affected Area: Leaf, Growth, and Fruit

Description: Generally, infected plants respond with a variety of symptoms, including green veinbanding, mosaic, spotting, blisters, ring spots, and protrusion of veins at the leaf margin. Plants are often stunted, producing malformed and mottled fruits.

Control: The best forms of control include using virus-free seed and applying insecticides to control the beetle vectors.

Problem: Squash Vine Borer
Affected Area: Vines, Stalk, and Petioles

Description: Burrowing in vines and stalks can cause wilting of the plant. A telltale sign of borer infestation is holes in vines or at the base of the petioles, from which greenish frass is extruded. Heavy infestations can considerably reduce yield.

Control: Chemical control with recommended insecticides should begin when eggs are found on foliage. The field planting should be turned under as soon as the crop is harvested.

Problem: Striped Cucumber Beetle
Affected Area: Seedlings

Description: Only cucurbit plants are attacked. The principal damage results from adults feeding on young seedlings. These beetles are also important as vectors of pathogens, which cause bacterial wilt.

Control: Newly germinated seedlings should be monitored regularly for beetles, and recommended insecticides should be applied as a foliar spray.

Problem: Thrips:
Affected Area: Leaf, Flower, Bud, and Fruit

Description: Adults and nymphs cause injury. Thrips feed by piercing the cells of bud, flower, and leaf tissues and then sucking plant juices from the feeding sites. They also feed on pollen. Feeding causes silver colored leaves, discoloration of flowers and buds and can result in fruit abortions. Small plants can be stunted and deformed.

Control: Insecticides are recommended for control and should be applied when thrips are present and damage is evident. Management of weeds within the crop is also recommended.

Problem: Tobacco Ringspot
Affected Area: Leaf and Fruit

Description: Newly infected leaves usually exhibit very bright yellow mosaic, ring spots, drying, distortion, and in some cases enations. During the first phase of infection, fruits tend to abort or remain small and become spotted and distorted.

Control: Intense cultivation and a methodical weeding program drastically reduce the presence of the vectors and the presence of the disease.

Problem: Tomato Ringspot
Affected Area: Leaf, Bud, and Fruit

Description: Infected plants react with yellow mosaic, reduction in leaf size, shortened internodes, proliferation of flower buds, and prominent ring spots on the discolored fruits. Generally, symptoms are very prominent in the initial, acute stage, which is followed by a chronic stage in which growth is mildly affected.

Control: Intense cultivation and eradication of weeds drastically reduce the presence of the virus in vectors.

Problem: Ulocladium Leaf Spot
Affected Area: Leaf

Description: Immature lesions are dark brown and 1-2 mm in diameter. As the lesions age, the central area becomes beige, surrounded by a dark brown ring and a circular brown halo, 6-7 mm in diameter. Several of these lesions may group together to form larger, irregular spots, but they retain their light beige centers.

Control: The best forms of control include using resistant cultivars, fungicidal sprays, and destroying old vines from cucumber fields.

Problem: Watermelon Mosaic
Affected Area: Leaf and Fruit

Description: Foliar symptoms include green mosaic, leaf rugosity, green veinbanding, yellow rings, and malformation. These symptoms often are very prominent in some winter and summer squashes, but affected leaves develop to nearly normal size. Fruits are not distorted, but green spots, particularly on yellow fruit, adversely affect some of their coloration.

Control: The best forms of control include using resistant cultivars, applying mineral oil sprays to interfere with virus transmission, and insecticides to control aphid populations and slow virus spread.

Problem: Whiteflies
Affected Area: NA

Description: Whiteflies damage cucurbits by direct feeding damage, by contamination with excrement on honeydew, and by inducing physiological or apparently phytotoxic disorders.

Control: Whitefly monitoring should begin at the time of seedling emergence. Yellow sticky traps can be used to trap adult whiteflies moving into a field and give an indication of when to initiate plant sampling for nymphs. Other components of a management plan include consideration of natural enemies, including predators, parasites, and pathogens.

Problem: Zucchini Yellow Mosaic
Affected Area: Leaf and Growth

Description: The virus incites yellow mosaic, severe malformation, blisters, and extreme reduction in the size of leaf lamina, drying, and severe plant stunting. Malformation is the greatest symptoms that will be observed.

Control: Resistant cultivars offer the only resistance that provides consistent control.



Cucumbers grow best in soil that is rich in organic matter.