CUCUMBER - INSECT
APHIDS
Cotton aphid: Aphis gossypii
17. Figure Aphis gossypii
Host range: The cotton aphid, Aphis gossypii (Hemiptera: Aphididae), is an extremely polyphagous aphid found on more than 700 plant species. It has a large range of host plants including cotton, cucumber, zucchini, melon, citrus, coffee, cocoa, eggplant, pepper and many ornamental plants.
Occurrence and importance: The cotton aphid is distributed throughout the world but prefers the warmer regions - from tropical and temperate regions throughout the world, except northern Canada and northern Asia. This aphid species is an important vector for viral diseases. It can transmit more than 50 different viruses, including the cucumber mosaic virus.
18. Figure Aphis gossypii sympthomes
Symptoms: Nymphs and adults extract nutrients from the plant. As a result, the plant’s growth is retarded giving rise to deformed leaves or, if the infestation occurs early enough in the season, the death of young plants. Retarded growth and defoliation reduce yield. Plants become covered with a black sooty mould which grows on the honeydew excreted by the aphid.
Description: The wingless adults are soft bodied, yellow to dark green, and about 1.0 to 1.5 mm long. The winged adult is also soft bodied and yellow to dark green. It has a black head and thorax. The winged form is about 1.25 mm long.
The cotton aphid can be distinguished from other aphids by the colour of the two cornicles (siphunculi). These cornicles are always black, whatever the body colour, which can vary widely, from light yellow to light green, or even a green-black colour.
Life cycle: Aphids have a complex life cycle, with both winged and wingless forms of adults and a great variety in colour. In greenhouses reproduction takes place by parthenogenesis, with unfertilized viviparous females continuing to produce new generations of females. Aphids moult four times before reaching adulthood. In warm climates live young are produced all year, while in cooler areas there is an egg stage. Many generations can occur each year.
Control:
- Pest monitoring: Check plants frequently after transplant or seedling emergence. Aphid often are concentrated in "hot spots." Examine for presence of biological control agents; i.e., the presence of predators, parasites (aphid mummies), and disease. Aphid flights are most common during periods of moderate temperatures. Monitor plants particularly closely during April and May.
- Biological control: Many parasites (Aphidius spp.) and predators attack aphids. Monitor the proportion of aphid mummies to unparasitized adults and the number of predators such as lady beetles. If the biocontrol agents appear to be gaining control, avoid sprays which would disrupt this system.
- Cultural control: Aphids can be washed from plants with a strong stream of water. Destroy infested plants immediately after harvest to prevent dispersal. Aphid populations tend to be higher in plants that are fertilized liberally with nitrogen.
- Chemical control: Insecticides, horticultural oil, insecticidal soap, kaolin, plant-derived essential oils (rosemary, peppermint etc.), pyrethrins (often combined with other ingredients).
Green peach aphid: Myzus persicae
Host range: Myzus persicae (Hemiptera: Aphididae) infests a wide range of plants. Some important hosts include cabbage, tomato, tobacco, potato, spinach, pepper, eggplant, legumes and others.
Occurrence and importance: Green peach aphid is found all over the world, including the tropics and temperate latitudes. In addition to attacking plants in the field, green peach aphid readily infests vegetables and ornamental plants grown in greenhouses. This allows high levels of survival in areas with inclement weather, and favours ready transport on plant material. Direct damages to plants are usually of minor importance but this species transmits almost 200 plant viruses among which ZYMV, CMV and WMV are the most important for cucumber.
Symptoms: M. ersicae commonly occurs as individuals only and does not form colonies on cucumbers. That is why symptoms caused by sucking are usually not visible on cucumber plants.
Description of the pest: The green peach aphid is soft-bodied and pear-shaped, ranging from 1.6 to 2.4 mm long with piercing-sucking mouthparts. Aphids are usually wingless. The wingless green peach aphid adult is pale-yellow to green. In the fall, colour may range from pale- to dark-green to pink or red. The winged migrant form has a yellowish green abdomen with a dark dorsal blotch.
Life cycle:
20. Figure: Life cycle of Myzus persicae
Life cycle of the green peach aphid varies depending on temperature. A fully completed generation takes approximately 10 to 12 days with over 20 annual generations reported in mild climates. Aphids overwinter on Prunus plants and once plants break their dormancy, the eggs hatch and nymphs feed on the flowers, young foliage and stems of the plant. After several generations, winged individuals deposit nymphs on summer hosts. In cold climates, adults will return to Prunus plants in the autumn, where mating occurs and eggs are then deposited. All generations except the autumn generation culminating in egg production are parthenogenetic (non-sexual).
Control
- Mint (Mentha haplocalyx), mung bean (Vigna radiata), celery (Apium graveolens) and coriander (Coriandrum sativum) planted near ventilation openings could be used to control M. persicae infestations in commercial greenhouses;
- Early planting and timely replanting of repellent plants is a more effective, environmentally friendly and suitable method for organic pest control compared with chemical pesticides;
- Biological control – parasitoids Aphidius, predators Harmonia axyridis and Aphidoletes aphidimyza. Make an effective combination of neonicotinoid insecticides or other selective insecticides and biological control agents;
21. Figure How the A. colemani organic control works
- The first effective choice to spray would be either insecticidal soap or horticultural oil. These insecticidal products coat the aphid’s exoskeleton (body)and cause it to suffocate. Applications should be made when temperatures are cooler, such as the mid- to late evening to avoid any potential plant damage.
- An effective step up from the soaps and oils, are insecticides that contain the active ingredient pyrethrin. This botanically derived compound can be very effective in providing a relatively quick knockdown of aphids.
- Another effective botanically derived chemical is azadirachtin. This compound is a natural insect growth regulator that modifies the way insects grow by inhibiting the shedding of the exoskeleton. It can be mixed with an entomopathogenic fungi or bacteria to allow more contact time between the insect’s exoskeleton and the pathogenic organism. This ensures that the fungi or bacteria have time to grow, penetrate the exoskeleton, and kill the insect.
- Systemic insecticides are available for the control of aphids. The later provides less impact to potential pollinators and natural enemies, as the chemical is applied directly to the roots and taken up by the plant.
12. Figure Powdery mildew is a commonproblem when growing cucumbers
THRIPS
Western flower thrips: Frankliniella occidentalis
22. Figure Frankliniella occidentalis
Host range: Western flower thrips have a broad host range of more than 500 species in 50 plant families and are associated with many cultivated crops and ornamentals. Crops attacked by this pest include beans, capsicum, cucumber, eggplant, lettuce, onion, tomatoes and watermelon.
Wide host range - more than 500 species in 50 plant families. Some examples are: soft fruit (plums, peaches, strawberries, grapes); flowers (Gladiolus, Impatiens, Gerbera, Chrysanthemum, poinsettia); vegetables (cucumber, tomato, capsicum, cabbages, beans), both in the field and in greenhouses.
23. Figure: Distribution of Frankliniella occidentalis
Occurrence and importance: Western flower thrips are among the most economically important agricultural pests globally, attacking a wide range of vegetable and horticultural crops. In addition to causing extensive crop damage, the species is notorious for vectoring destructive plant viruses.
24. Figure: Symptoms of thrips
25. Figure: Symptoms of thrips
Symptoms: Symptoms of plant damage by thrips feeding include: bud deformation, shape distortion of fruits or vegetables during growth and a range of leaf spots, scars, silvering and bronzing. Both adult and larvae feed throughout the plant and leave the crop susceptible to secondary fungal and bacterial infection resulting in moulding and wilting. The western flower thrips is a vector of some important virus diseases such as Melon yellow spot virus.
Description of the pest: occidentalis are small (1-2 mm long), slender, soft-bodied insects that are yellow to light brown in color; adults have distinctive fringed wings.
The female is about 1 mm long, larger than the male, with pale forewings. The colour of the female varies from yellow to dark brown, being darker at low temperatures, yellowish at higher temperatures. The male is always pale yellow and has a narrower abdomen. The larvae are yellow, becoming paler towards moulting.
Life cycle: A life cycle, from oviposition to adult emergence, may require two weeks in warm weather, to about six weeks in cool weather. The adults live for several weeks; the arrhenotokous females, deposit 50-100 eggs during their lives. They develop through two quiescent, non-feeding pupal stages in the soil, in plant litter or in protected areas on the host plant. As long as environmental conditions are favourable, Frankliniella occidentalis will reproduce continuously, with up to 15 generations in a year. Life cycle can vary between 13 and 40 days dependent on temperature.
Control:
- Monitoring: Monitoring the population levels of western flower thrips is critical for successful pest management. Commercially available blue or yellow sticky traps can be used to monitor the population densities of adult thrips. Blue traps are more attractive to western flower thrips.
- Cultural control: Sanitation is the first and most important step in implementing an effective pest management program. Cultural control measures also include maintaining a healthy crop and an optimal greenhouse environment (such as 80% relative humidity), creating less favourable conditions for a rapid increase in the density of thrips populations.
- Physical control: Use screens to restrict the movement of insects into the greenhouse.
- Biological control: Because thrips have developed resistance to most registered pesticides, biological control is now the primary strategy for controlling thrips in greenhouse crop production. Biological control agents include predatory mites such as: predatory mites (Neoseiulus (= Amblyseius) cucumeris, Amblyseius swirskii, Stratiolaelaps scimitus (= Hypoaspis miles), Gaeolaelaps aculeifer (= Hypoaspis aculeifer), Orius spp., nematodes (Steinernema feltiae), the fungal insect pathogen Beauveria bassiana.
- Chemical control: The pest is resistant to most pesticides and feeds deep within the flower head or on developing leaves. This makes them a difficult target for insecticides, so thorough coverage is essential. Thrips are more easily managed when population levels are low. Apply pesticides in early morning or late afternoon, when flight activity of thrips is at a peak. This increases exposure of the thrips to the pesticides.
WHITEFLIES
Bemisia tabaci MEAM1 and MED (also recorded as Biotype B and Biotype Q)
27. Figure Bemisia tabaci
26. Figure Bemisia tabaci
Host range: The tobacco whitefly (Bemisia tabaci) (Hemiptera: Aleyrodidae) has an enormous host range and affects an extremely wide range of crops throughout the world, with host plants in 800+ species, assigned to 90+ plant families, and the number of recorded hosts is continually increasing. They include crops grown outside in the tropics and sub-tropics (e.g. cassava, cotton, sweet potatoes, tobacco and tomato), vegetable and salad crops grown under glass in Europe (e.g. cucumber, aubergine, pepper and tomato) and ornamental plants (e.g. poinsettia).
28. Figure: Distribution of Bemisia tabaci
Occurrence and importance: Bemisia tabaci is one of the most economically-important agricultural and horticultural pests in the World, due in part to its adaptability, extreme host plant range and capacity to vector more than a 110 plant pathogenic viruses. It is not a single species but a complex of many taxa that are only distinguishable at the molecular level and the taxonomy has not yet been resolved. This is significant as different ‘biotypes’ or ‘species’ within the complex vary in biological characteristics such as host preferences, ability to vector viruses and pesticide resistance.
The B biotype is the most widespread biotype on a worldwide scale (it belongs to the Middle East Asia Minor 1—MEAM1 group) and is hypothesized to originate from the Middle East–Asia Minor region.
Until the 1980s, B. tabaci was considered to be a pest of field crops in tropical and subtropical regions, but is now widely distributed under glass in temperate areas, including most of Europe.
29. Figure Bemisia tabaci symptoms
Symptoms: Btabaci causes damage directly by feeding, and indirectly by honeydew egestion and virus transmission. Feeding by adults and larvae causes chlorotic spotting, growth distortion, and premature leaf drop. The honeydew egested by the feeding larvae covers the surface of the foliage and fruit and serves as a medium for the growth of sooty moulds. This reduces the photosynthetic potential of the infested plant. Honeydew and moulds also disfigure and lower the market value of fruit and flowers. However, it is the viruses vectored by B. tabaci that have the greatest economic impact. Whiteflies are vectors of plant viruses from the families, Begomoviruses, Coronaviruses, Ipomoviruses, Torradoviruses and some Carlaviruses, which can cause total failure of susceptible crops.
Description of the pest: Adult: About 1 mm long, the male slightly smaller than the female. The body and both pairs of wings are covered with a powdery, waxy secretion, white to slightly yellowish in colour. Egg: Pear shaped with a pedicel spike at the base, approximately 0.2 mm long. Larva: Yellow-white scales, 0.3-0.6 mm long. Puparium: Flat, irregular oval shape, 0.7 mm long. On a smooth leaf the puparium lacks enlarged dorsal setae, but if the leaf is hairy, two to eight long dorsal setae are present.
Life cycle:
30. Figure Life cycle of Bemisia tabaci
All whiteflies have six developmental stages: egg, four larval instars, and the adult. Each female lays up to 160 eggs on the undersides of the leaves. Hatching occurs after 5-9 days at 30°C, depending on host species and humidity. The first instar or 'crawler' is flat, oval and scale-like, and is the only mobile larval stage. It moves to a suitable feeding location where it moults and becomes sessile throughout the remaining larval stages. The first three nymphal stages last 2-4 days each whereas the fourth larval stage or puparium lasts for about 6 days, dependant on the temperature. The adult emerges through a 'T'- shaped rupture in the pupal case and expands its wings before powdering itself with wax from glands on the abdomen. Mating begins 12-20 hours after emergence and takes place several times throughout the life of the adult. A female may live for 60 days, although the life of the male is generally much shorter, being between 9 to 17 days. Up to 15 generations can occur within one year.
Control:
- Cultural Control: Intercropping practices using non-hosts can be used aiming to reduce numbers of whiteflies. Weed species play an important role in harbouring whiteflies between crop plantings and attention should be paid to removing these in advance of planting susceptible crops.
- Biological Control: Conservation of natural enemies is important in field crops. Predatory mites have been shown to be efficient against B. tabaci. Entomopathogenic agents such as fungi have also been shown to be important biological tools in the control/eradication of B. tabaci.
- Host-Plant Resistance: Plant and crop species that exhibit a high level of resistance to both vector and virus must also be considered when designing an IPM system.
- Chemical Control: B. tabaci appears to develop resistance to all groups of pesticides that have been developed for its control. A rotation of insecticides that offer no cross-resistance must therefore be used to control B. tabaci infestations.
- Integrated Pest Management: IPM appears to offer the best option for controlling B. tabaci without causing contamination of the environment: beneficial insects are used alongside chemicals that offer a high level of selectivity such as insect growth regulators. However, the use of biological control agents alone, such as Encarsia formosa and Lecanicillium lecanii or Beauveria bassiana although moderately successful, can never bring infestation levels down to a level that stops virus transmission, as B. tabaci is such an efficient virus vector.
- Phytosanitary Control: In countries and regions where B. tabaci is not already present, the enforcement of strict phytosanitary regulations should help reduce the risk of this whitefly becoming established.
SPIDER MITES
31. Figures: Tetranychus urticae Koch symptoms
32. Figures: Tetranychus urticae Koch symptoms
The mite is strictly phytophagous pests, on the lower surface of leaves more than upper surface, and this depends on the species and both surfaces may be occupied during high infestations. Feeding on plant cells produces leaf yellowing and bronzing and heavy damaged leaves that become brown on the upper surface. The undersurface of leaves may have a greyish cast due to webbing where there is leaf deformity and tissue death.
Description of the pest: Two spotted spider mites, Tetranychus urticae, are tiny, oval, eight legged creatures about 0.4 - 0.6 mm long. They characteristically have two (sometimes four) dark spots on the back. They are typically yellow or greenish amber but overwintering females are red to orange. Two spotted spider mite nymphs are smaller and can be brownish-green but otherwise resemble adults. Eggs are colourless or white spheres usually found on the leaf’s underside.
33. Figures: Tetranychus urticae Koch
34. Figures: Tetranychus urticae Koch
Life cycle: The life cycle is composed of the egg, the larva, two nymphal stages (protonymph and deutonymph) and the adult. The length of time from egg to adult varies greatly depending on temperature. Under optimum conditions (approximately 270C), spider mites complete their development in five to twenty days. There are many overlapping generations per year. The adult female lives two to four weeks and is capable of laying several hundred eggs during her life. The two-spotted spider mite prefers the hot, dry weather of the summer and fall months, but may occur anytime during the year. Overwintering females hibernate in ground litter or under the bark of trees or shrubs.
35. Figure Life cycle of Tetranychus urticae Koch.
Life cycle: The life cycle is composed of the egg, the larva, two nymphal stages (protonymph and deutonymph) and the adult. The length of time from egg to adult varies greatly depending on temperature. Under optimum conditions (approximately 270C), spider mites complete their development in five to twenty days. There are many overlapping generations per year. The adult female lives two to four weeks and is capable of laying several hundred eggs during her life. The two-spotted spider mite prefers the hot, dry weather of the summer and fall months, but may occur anytime during the year. Overwintering females hibernate in ground litter or under the bark of trees or shrubs.
Control:
- Cultural Control - Cultural controls for spider mites mainly involve reducing plant stress and ensuring the plant’s environment is not conducive for spider mite development.
- Biological Control - Micro- and macro-organisms for the control of urticae -predatory mites Phytoseiulus persimilis, Amblyseius californicus, Amblyseius swirskii, etc., predatory midge, predatory bugs.
- Chemical Control - When all other control measures have failed to keep the populations under control, a chemical miticide may be needed. The primary goal with miticide use is to choose the one with minimal impact to pollinators and natural enemies, but still be effective on the insect causing the problem. The first effective choice to spray would be either an insecticidal soap or horticultural oil.
36. Figure Tetranychus urticae Koch
SEED CORN MAGGOT
Delia platura (Meigen) (Diptera: Anthomyiidae)
37. Figure Adult Seedcorn Maggot
Host range: The seedcorn maggot is a polyphagous pest, affecting more than 40 different host plants. It is an important pest of germinating soybeans and corn. It also attacks a wide range of horticultural crops including beans (Phaseolus spp.), peas (Pisum spp.), cucumber (Cucumis sativus), melon (Cucumis melo), onion (Allium cepa), pepper (Capsicum annuum), potato (Solanum tuberosum), and other vegetables.
Occurrence and importance: Cucumbers can be infested by seed corn maggot in some localities but losses are usually not important on larger plots.
Symptoms: The maggots feed on developing seed and can completely destroy the seed, or damage the cotyledons and first true leaves, causing holes, tunnels and secondary rots in cotyledons and tops of plants. Severely affected plants are stunted or die. Early infested plants do not emerge.
38. Figure Sympthomes of Seedcorn Maggot
39. Figure Larvae of Seedcorn Maggot
Description of the pest: Seed corn maggot is similar to common house fly, about 4 - 6 mm long, grey coloured with brown legs. Eggs are glossy white, about 1 mm long and 0,3 mm in diameter. Larva is about 6 - 8 mm long, whitish, legless and without visible head. Puparium is 4 - 5 mm long, brown.
40. Figure Distribution of Delia platura
Life cycle: Puparium is the overwintering stage. Adults hatch at the end of April or beginning of May. They lay their eggs to the vicinity of sown seeds or young emerging plants. Larvae make tunnels in cotyledons or top of the plant. Fully developed larvae pupate in soil. Seed corn maggot has three generations during a year.
Control:
- Sanitation practices such as removal of flowering weeds from outlying areas to eliminate nearby food sources for adult flies and removal of sweet smelling substances decreases the attractiveness of an area to these flies;
- Recent (3 weeks and less) disking of residues of previous crops increases risk of
attack; - Early planted plants are more often infested, avoid planting into cool and wet soil;
- Seed treatment is one of the least expensive and most effective treatments for control of seed corn maggot.
Listo of Viruses:
- WHITEFLY-TRANSMITTED VIRUSES
- BEET PSEUDO-YELLOWS VIRUS [BPYV]
- CUCURBIT YELLOW STUNTING DISORDER VIRUS [CYSDV]
- ZUCCINI YELLOW MOSAIC VIRUS
- CUCUMBER MOSAIC VIRUS AND WATERMELON MOSAIC VIRUS
- DOWNY MILDEW
- DAMPING OFF
- POWDERY MILDEW
- ANTHRACNOSE
- PHYSIOLOGICAL FLOWER FALL OFF
- FLOWER DROP
- APHIDS
- THRIPS
- WHITEFLIES
- SPIDER MITES
- SEED CORN MAGGOT