SPIDER MITE: DESCRIPTION OF THE MOST FAMOUS SPECIES — PEST CONTROL

Types of spider mites with description and photo

Spider mite is one of the most terrible and hated enemies of all gardeners. Ticks often survive in hot, dry conditions, unfavorable to many other parasites. Sooner or later every gardener came across this pest. Consider why the attacks of spider mites are so dangerous and unpleasant that they do with our plants, what types of parasite are and how to fight them.

Spider mite: general characteristics of the pest

Spider mites are malicious pests that colonize the leaves of houseplants and horticultural crops. These parasites are detected everywhere. Spider mite is extremely small, which makes it difficult to fight it. It is impossible to notice the parasite until serious damage to the leaves of the plant occurs. The length of the female individual is only 0.4-0.6 mm, the male is even smaller. The color of ticks is pale green or amber yellow.

Such pests as caterpillars, nematodes, aphid, cockchafer, carrot fly, onion fly and snail significantly affect the general properties of plants, and in some cases can lead to their complete death.

Did you know? Spider mite is not an insect. It is classified as arachnid class, a relative of spiders and scorpions. The main feature that distinguishes mites from insects is the number of limbs. Insects have three pairs of legs, ticks have four pairs.

The spider mite is usually located on the back of the leaf blade, where it sucks the sap of the plants and makes many small holes. Damaged leaves are dehydrated. They look dry, fragile and discolored. Even a minor infection can have a significant impact on plant development. And with a long attack, the plant’s ability to photosynthesis and self-healing decreases. Leaves infected with pests can suddenly become covered with a thin web, turn yellow and fall off. Plants in general are becoming weaker.

Did you know? Spider mites are especially dangerous, as they can severely damage a plant in a short period. MicroscopicArazites attack in large numbers, this is the cause of serious damage to the foliage. Among the plant pests are mitessome of the most difficult to control, which is why pesticides have to be used.

Types of spider mites and their description

There are many species of spider mites, and some may be more common in your area than others. Most species attack both internal and external parts of plants.

Common Spider Mite

The common spider mite infects plants in the dry summer. Damage from the pest is manifested in leaf spot. It may be white, yellowish or reddish brown. Tick ​​eggs can be found on the leaf blade of the plant. Sometimes there is damage to the leaves: they are torn between the veins, dry and fall. In turn, such damage can have a negative impact on the yield and quality of fruits.

Next, consider what a spider mite looks like. The length of an adult tick is 0.44–0.57 mm, the body is oval, pale yellowish or greenish in color. The body of an adult male is slightly smaller than that of the female, narrower and has a yellow-green color. At a temperature of 22 ° C and a sufficient amount of food females live from 21 to 35 days. One female can lay several hundred eggs. In the spring, females migrate to grassy terrestrial vegetation and begin laying eggs. They are translucent, spherical in shape.

The pest attacks plants during the growing season. In the case of a massive reduction in summer plantings or in the treatment of plants with herbicides, pests look for other food sources. Parasites can settle in the root system of a plant. The same happens if there is no precipitation. This enemy of plants has a high potential of distribution. In particular, in hot dry weather, two parasites create up to seven generations during the growing season. Accordingly, the damage becomes more pronounced and appear as soon as possible.

In greenhouse conditions, the spread of the common mite is much faster because of the higher chances of survival in the heat. The cracks and crevices of the greenhouse construction are the perfect shelter for the winter for the parasite, which greatly complicates the fight against it. The number of ticks in a greenhouse increases by more than 50 times (from 10 to 15 generations) within 2-4 weeks. Pests prefer such plants: pepper, eggplant, cucumber, carnation, gerbera, rose, chrysanthemum, but most often the parasite affects everyone’s favorite indoor ficus. If you have identified a thin whitish web on the trunk of a ficus, this is a sign of infection and a signal that something needs to be done.

Important! Ticks are very difficult to see with the naked eye. To identify small pests need a magnifying glass. To determine the type of such an organism, you can also contact your local phytosanitary service for help.

False spider mite

False spider mites are destructive and rare small pests. This species differs from other members of the family in that it does not spin a web. In addition, the false mite is smaller in size than other species. An adult individual has a flat red body about 0.25 mm in length with two pairs of short legs in front and two pairs of legs adjacent to the narrow abdomen. Eggs are red, oval, deposited singly near the main veins on the back of the leaf. The nymph is similar in shape to an adult.

These small enemies of plants move slowly and are sometimes visible on the back of the leaves. They feed on the upper and lower layers of leaves, which leads to the death of the plant. This type of mite affects citrus fruits, orchids, passionflora, papaya, rambutan, durian and mangosteen. Infection usually occurs in hot, dry weather and causes scarring and discoloration of ripening fruits.

Did you know? The damage of citrus fruits by a false spider mite is unusual: ticks tend to infect those parts of the fruit that have already been damaged by other insects.

Atlantic spider mite

Atlantic spider mites (Tetranychus atlanticus) — a look similar to an ordinary, false and Turkestan tick. The Atlantic mite is able to live and multiply at very high humidity of the air and the soil. The color of the calf is yellowish-green. The length of the female specimen is 0.43–0.45 mm; body oblong-oval, convex. Females usually hibernate at the base of plants and other dark areas. During the season, the parasite reproduces 5-6 generations. The length of the male is about 0.3 mm. Eggs are spherical, light.

The parasite chooses palm trees and citrus fruits as places of settlement. Ticks infect fruit, vegetable, berry, technical and ornamental plants. When attacking ticks on foliage, yellow formations are noted. Gradually the spots cover the whole leaf, which eventually leads to its drying.

Red spider mite

Red spider mites (Tetranychus cinnabarinus) — garden pests affecting a wide variety of plants: azalea, camellia, apple, citrus, carnation. But most often this spider mite settles on a cactus. This fact is explained by the fact that these parasites prefer dry habitat. Ticks multiply rapidly in drought conditions and show resistance to certain pesticides. Small enemies of plants suck sap from a young cactus, forming white spots on its surface.

After infection with this pest, the plant is continuously damaged. Leaves take an unhealthy look. On the reverse side of the sheet plate is observed dusty deposits. A careful inspection reveals that this dust «moves» and is in fact a cobweb. The red spider mite is most active in cool weather (spring or autumn).

Eggs whitish-pink spherical shape. The larva is yellowish-greenish with three pairs of legs. The nymph is yellowish gray, with dark spots, has four pairs of legs. Depending on age, the color of ticks varies from yellowish to brownish red. The body of an adult female is oval, 0.4 mm in length. Males are slightly smaller — 0.35 mm.

The question of how to control a red spider mite and how to get rid of it is complicated by the fact that mite eggs can remain in the soil for about five years.

Cyclamen spider mite

Cyclamen spider mite (Tarsonemus pallidus) causes serious damage to various greenhouse crops. Adult individual with a length of less than 0.3 mm. On the legs are placed microscopic suckers. Colorless or brown, they have four pairs of limbs. The length of a smooth egg is 0.1 mm.

Cyclamen mites avoid light, they are found in hidden shady places on houseplants (in the buds, between the calyx and corolla). In addition, cyclamen mites prefer high humidity. Parasites feed on young leaves and plant buds. Infected leaves curl inward and become wrinkled. Buds also look wrinkled and discolored, and sometimes they may not open at all. This pest has a wide range of host plants: violet, cyclamen, dahlia, chrysanthemum, geranium, fuchsia, begonia, petunia, daisy, azalea.

Turkestan spider mite

Turkestan Spider Web mite — pest size 0.3-0.6 mm, green. A common greenish color results from eating the cell sap of plants with a high content of chlorophyll.

The length of the female is 0.5-0.6 mm; the shape of the calf is ovoid. Females overwinter in small settlements on weeds, fallen leaves, bark cracks. Their life expectancy is 80 days. The male is slightly smaller than the female, the shape of the calf is elongated, the color is light green.

The leaves infected with this pest turn yellow and become covered with thick cobwebs. Gradually, leaf blades are noticeably damaged. Water balance is disturbed. Suspended photosynthesis. The leaves dry out. The parasite damages melons and vegetables, as well as beans and cotton.

Wide spider mite

High humidity and high temperatures contribute to the development wide spider mite (Tarsonemus pallidus). Severe outbreaks can occur in greenhouses during the fall and winter months. Spider mite is most often found on balsamic (we will return to the question of how to deal with it).

The body of this pest is translucent, light green in color. Females can live up to one month and breed without mating. They lay 2-3 eggs per day for 2-3 weeks. During the entire life cycle, one female lays up to 16 eggs in moist dark places in crevices and at the base of the plant. They are oval, smooth. White larvae hatch in 2-3 days. Adults leave the pupal stage after 5–7 days, and tend to move faster. They can complete a life cycle in just 1 week.

Through saliva, parasites spray a dangerous toxin onto the plant. The leaves become twisted, hardened and distorted, there is a bronze coating on the lower surface of the sheet. With the mass spread of the parasite, the young buds of the plant may die. The damage resembles the usual disturbances in plant development.

See also:  Wireworm - Control of Wireworm Pests in Garden Soils

This pest often feeds on flower crops. Flower spider mite has a wide range of host plants: violet, ageratum, begonia, chrysanthemum, cyclamen, dahlia, gerbera, gloxinia, hibiscus, jasmine, balsam, lanthanum, marigold, snapdragon, vervain, zinnia. Sometimes a broad tick infects crops such as peppers, tomatoes, and legumes.

With a large number of pests it is recommended to spray the plants with such chemical preparations as Fufanon, Bi-58, Tanrek, Alatar, Aktara, Aktellik, Karbofos and Fytoverm.

Top Spider Mite Tips

Experienced gardeners and specialists involved in the fight against spider mites, lead Some important tips for the prevention and treatment of plants from this pest:

  • Of course, the best means of pest control is prevention. Only a healthy plant can repel pest attacks. The weaker is more susceptible to parasites. Work to keep the plants healthy and the areas around them free from debris and dust. Also, make sure that they are supplied with enough water. Active spraying and increasing irrigation will help control the level of infection. Water keeps parasites as they prefer a hot dry environment. Cooler and wetter conditions slow the rate of reproduction. In the open air, spider mites are active in spring and sleep in winter. The risk of pests is always higher if you live in a region with warm winters.
  • If you decide to use pesticides as a control against spider mites, always follow the instructions in the instructions. Some pesticides are not intended for food crops. Make sure the pesticide is not harmful to humans! Insecticidal oils are particularly effective. For detailed chemical control advice, consult your local phytosanitary service.
  • A great way to deal with garden pests is to use insect predators. Spider mites have natural enemies, including predatory mites, which can serve as a form of biological control. Usually use ladybugs. They eat ticks if there are no other insects around (for example, aphids). However, do not overdo it with the number of beneficial insects introduced. If you plant several thousand ladybirds in your garden, they will eat everything, including their own kind.

Important! Be careful with the amount of pesticides used. Chemicals from spider mites can kill beneficial insects, while pests will simply move from the pesticide-treated area to a clean area.

gb.farmforage.com

Gloxinia

Related terms:

Download as PDF

About this page

Gloxinias, African Violets, and Other Gesneriads

II. Sinningia speciosa—FLORISTS’ GLOXINIA

Sinningia speciosa was first named Gloxinia speciosa in 1817 by Conrad Loddiges, an English nurseryman, after he had studied the new plant from Brazil. Gloxinia is the common name used in commercial floriculture.

Sinningia speciosa has one or more stems with paired leaves. The blade of the leaf is a large and very pubescent. The bell-shaped flowers are approximately 2 inches wide and usually pale lavender. They are produced on plants 4 to 6 inches tall, although the size may be variable. The type species came from Brazil. Most florists” gloxinias are of the convariety fyfiana, the name originating for Gloxinia × fyfiana ( Moore, 1957 ). The red cultivars are commercially most popular ( Fig. 1 ).

Fig. 1. . Gloxinia greenhouse production.

Through hybridization and selection, gloxinias may be large-growing cultivars for 5- to 6-inch pots or compact types grown in 4-inch pots. Depending on the type, they may be single- or double-flowered, with colors ranging from pure white through pink, lavender, and red, to dark purple. Popular single cultivars include the ‘Velvet’ series, the ‘Bridget’s Best’ series, and Small’s “Super Compact” series for 4-inch pots.

Plants are grown from seed for commercial production. A plant with a large single head of flowers can be produced using this method in approximately 6 to 7 months in a 5-inch pot or 5 to 6 months in a 4-inch pot.

There are some specialists who produce and sell seedlings. The seeds are sown on a soilless medium and placed under intermittent mist in a shaded house at 70°F night temperature for rapid germination. When the seedlings are large enough to handle, they are transplanted into 2 ½-inch pots. Either plastic or clay pots may be used successfully. A soilless medium including peat moss, sand, perlite, and vermiculite can be used. When the seedlings are approximately 3 months old, they are shipped to the grower, where they are transferred into the final pot.

The seedling production procedure can also be used by the retail or wholesale grower if warm greenhouse conditions are available and space is not limited. When the seedlings are transplanted by the grower, it may be easier to transplant the seedlings into flats as soon as they can be handled. The plants should be spaced 1 to 2 inches apart. When the foliage of the plants begins to touch, the plants should be transferred to a 4-, 5-, or 6-inch azalea pot, depending on the finished size of the cultivar being grown. Plastic or clay pots may be used with success.

The media for growing the transplanted seedlings can be soilless mix or a soil mixture such as 1:1:1 (light organic soil, peat moss, and coarse sand or perlite, on a volume basis). A pH of 6.0 should be obtained by adding dolomitic limestone to the medium. Plants may be potted with the bottom two leaves buried in the pot for a more sturdy finished plant, should be spaced on 10-, 12-, or 16-inch spacing, and watered immediately. It is very important that water not be allowed to remain on the foliage. A fungicide can be added with the water to prevent disease from injuring roots or leaves, especially if the plants are shipped.

The best production of gloxinias is achieved at a night temperature of 70°F. Optimum growth can be obtained with a radiant flux of 19.4 to 26.9 klx. The growing medium should never be allowed to become dry. Tube watering and mat watering methods have been used with excellent results. The fertilization program should begin immediately after transfer to the finishing pot. A complete fertilizer (such as a 15–16–17 peat-lite special) can be alternated with calcium nitrate at the rate of 2 pounds per 100 gallons of water. Fertilization is recommended every 10 days and is increased as the plants grow larger. Some growers do use a 200 ppm nitrogen, phosphorus, and potassium constant fertigation program using 15–15–15 or 20–20–20 at 2 to 3 pounds per 100 gallons. There have been some problems in the winter using the 20–20–20, which is high in ammoniacal nitrogen. Osmocote at ¼ to ½ teaspoon per 6-inch pot can be used effectively. With sufficient natural light and temperature, additional lighting should not be necessary. If, however, the night temperature is 60°F, additional lighting may be beneficial to reduce flower delay. Good results are obtained with 100 watt incandescent bulbs spaced 4 feet above the plants and turned on 4 to 5 hours each night. The additional lighting seems most effective immediately after the seeds have germinated. When plants are well budded, more uniform flowering may be obtained by removing the first two flower buds as soon as color is evident.

The use of chemicals to control plant height might be necessary, particularly in the summer when heavy shade to reduce temperature causes stretching of the internodes. Sweet (1983) noted that B-Nine, at a diluted strength of 1000 ppm in solution, worked well when applied 1 to 2 weeks after transfer into the finished pot. He noted that late application would not shorten the plant enough to be a quality plant. Sydnor et al. (1972) found that B-Nine applications resulted in compact plants and that flower color was intensified on pink cultivars used in the study.

Mites

Phytonemus pallidus (Banks) (1123)

syn. Tarsonemus pallidus Banks

Cyclamen mite

A major pest of greenhouse ornamentals, including African violet (Saintpaulia hy brida), azalea (Rhododendron), Begonia, busy lizzie (Impatiens), Cyclamen, Gerbera, Gloxinia , ivy (Hedera), Japanese aralia (Fatsia japonica), Pelargonium, Petunia and Verbena. In favourable situations infestations also survive on outdoor plants. Distinct biological races are associated with Michaelmas daisy (Aster) and strawberry — Phytonemus pallidus asteris and P. pallidus fragariae, respectively. Virtually cosmopolitan. Widely distributed in Europe.

1123 . Cyclamen mite (Phytonemus pallidus) damage to leaf of Fatsia.

Description

Adult female: 0.25 mm long; light brown and translucent; body oval-elongate and somewhat barrel-shaped; gnathosoma longer than broad, with the palps directed forwards; hind legs very thin, each bearing a long, whip-like seta. Adult male: 0.2 mm long; light brown and oval-bodied; hind legs broad, each with a very large femur bearing a rounded inner flange and terminating in a strong claw. Egg: 0.125 x 0.075 mm; elliptical, semitransparent and whitish. Larva: whitish, with hind part of body triangular; 6-legged.

Life History

In greenhouses this species is active throughout the year, breeding continuously whilst conditions remain favourable. The mites are light-shy and tend to occur on the young, succulent tissue of host plants. All stages (eggs, larvae, quiescent nymphs and adults) shelter within leaf folds, amongst leaf hairs and between bud scales. As the tissue ages and hardens, the mites move to younger, more suitable feeding and breeding sites, commonly invading the still-furled leaves and unopened flower buds. The mites may also spread from plant to plant, particularly if leaves or shoots or adjacent hosts overlap, but they rarely if ever wander over the soil or the greenhouse staging. There are several overlapping generations annually, mites passing from egg to adult in about 2–3 weeks at temperatures of 20-25°C; the rate of development is much reduced at lower temperatures, the egg stage becoming particularly protracted. Although males occur, typically during the summer months, they are usually greatly outnumbered by females and reproduction is mainly parthenogenetic. There are also several overlapping generations annually on outdoor plants, populations reaching a peak in August or September, but breeding usually ceases completely during the winter months.

Damage

Infested foliage become brittle, discoloured and crinkled, the margins of young leaves often rolling tightly inwards; flower buds are also affected. Attacked plants are stunted and young growth significantly distorted; when infestations are severe, leaves, flower buds or complete plants may be killed. Mites on Michaelmas daisy plants, especially Aster novi-belgii, cause severe scarring of flower stems, affected ‘flowers’ being converted into rosettes of small, green leaves.

Insects

syn. Erythroneura pallidifrons (Edwards); E. tolosana (Ribaut)

Glasshouse leafhopper

A polyphagous, tropical or subtropical species. Well established in the warmer parts of Europe. In northern Europe, infestations occur mainly on greenhouse plants, including Calceolaria, Chrysanthemum, diviner’s sage (Salvia divinorum), Fuchsia, Gloxinia , heliotrope (Heliotropium), Pelargonium, primrose (Primula vulgaris), sweet-scented verbena (Aloysia citriodora) and tobacco plant (Nicotiana); in favourable areas, also found on outdoor plants such as chickweed (Stellaria) and foxglove (Digitalis purpurea).

31 . Glasshouse leafhopper (Hauptidia maroccana).

Description

Adult: 3.1-3.7 mm long; mainly pale yellow, with greyish or brownish markings, the latter forming a pair of distinctive, chevron-like marks on the elytra. Nymph: whitish.

Life History

Breeding is continuous throughout the year, all stages occurring on the underside of host plants. Eggs are deposited singly in the leaf veins and hatch in about a week at normal greenhouse temperatures. Nymphs feed for about a month, passing through five instars before reaching the adult stage. Adults survive for up to 3 months, each female depositing up to 50 eggs. The duration of the various stages is extended in cool conditions; development is greatly protracted during the winter, when the eggs often take a month or more to hatch and nymphal development lasts for two or more months.

Damage

Growth of heavily infested plants is checked and seedlings killed, but on most hosts damage is limited to specking, silvering or a blanched mottling of the foliage. Leaves are also contaminated by cast nymphal skins.

Bunyaviridae

List of other related viruses which may be members of the genus Tospovirus but have not been approved as species

Alstromeria necrotic streak virus [S: GQ478668 (N)] (ANSV)
Calla lily chlorotic spot virus [L: FJ822961; M: FJ822962] (CCSV)
Capsicum chlorosis virus( Gloxinia tospovirus) [L: DQ256124, M: DQ256125;S: DQ256123] (CaCV)
(Thailand tomato tospovirus)
Chrysanthemum stem necrosis virus [S(N): AF067068] (CSNV)
Groundnut chlorotic fan-spot virus [ S(N):AF080526] (GCFSV)
Iris yellow spot virus [L: FJ623474; M: AF214014; S: AF001387] (IYSV)
Melon severe mosaic virus [S: EU275149] (MSMV)
Melon yellow spot virus [L: AB061774; M: AB061773; S: AB038343] (MYSV)
Physalis severe mottle virus [S: AF067151] (PhySMV)
Polygonum ringspot virus [M: EU271753; S: EF445397] (PolRSV)
Tomato necrosis virus [M: AY647437] (TNeV)
Tomato necrotic ringspot virus [M: FJ947152; S: FJ489600] (TNRV)
Tomato yellow (fruit) ring virus [S: AY686718] (TYRV)
Tomato zonate spot virus [L: EF552435; M: EF552434; S: EF552433] (TZSV)
Watermelon bud necrosis virus [M: FJ694963; S: EU249351] (WBNV)

Mites

5.3 Distribution, Host Range, and Seasonal Occurrence

Broad mites are worldwide in distribution in both field and protected areas. P. latus has a wide host range in tropical and subtropical areas including 60 families of plants ( Li et al., 1985; Grinberg et al., 2005; Ferreira et al., 2006; Alagarmalai et al., 2009 ). In temperate climates it is a greenhouse pest throughout the year and a crop pest during the summer. Broad mites infest a great many ornamental plants such as African violet, azalea, begonia, Cannabis, chrysanthemums, cyclamen, dahlia, gerbera, gloxinia , jasmine, impatiens, lantana, marigold, snapdragon, verbena, and zinnia as well as crops such as apple, avocado, cantaloupe, castor, chili, citrus, coffee, cotton, eggplant, guava, papaya, pear, potato, sesame, string or pole beans, mango, tea, tomato, and watermelon ( Rice and Strong, 1962; Peña and Campbell, 2005; Grinberg et al., 2005; Ferreira et al., 2006 ).

Broad mite is a major pest in the tropical parts of the world year round. In subtropical areas it is a major pest during the summer and fall if weather conditions are warm and wet ( Li et al., 1985; Ferreira et al., 2006 ). In temperate areas it is a pest during the summer months, but under the right environmental conditions of heat and humidity it can cause severe damage—similar to TRM.

Miscellaneous Pests

Root-knot nematodes ( 1147 )

Root-knot nematodes (Meloidogyne spp.) attack the roots of various trees, shrubs and herbaceous plants. Infested roots become distorted and develop rounded or irregular galls. These galls measure anything from 1 to 20 mm across and often coalesce, causing considerable distortion. The nematodes also exacerbate the deleterious effects of pathogenic bacteria and fungi. Root-knot nematodes are associated mainly with light soils but most damage is caused under glass, particularly in hot conditions where certain tropical and subtropical species, e.g. the Javanese root-knot nematode (Meloidogyne javanica), have become established. Pot plants such as Begonia, Coleus, Cyclamen, Gloxinia and various cacti may suffer considerable damage, severely affected plants appearing discoloured, lacking vigour and wilting under stress. Northern root-knot nematode (Meloidogyne hapla) is a widely distributed, polyphagous pest in northern Europe; it attacks many different kinds of plant, including various ornamentals. Root-knot nematodes invade host plants as second-stage juveniles; these settle down to feed in the young roots and usually reach maturity about 1–2 months later. Adult females are translucent-whitish, pear-shaped and about 0.5-1.0 mm long. They may be found within the galled tissue, often attached to a gelatinous sac that contains masses of eggs. In some cases development of the pest is parthenogenetic; in others, minute worm-like males mate with the females before eggs are laid. First-stage juveniles develop within the eggs, second-stage individuals eventually breaking free and either migrating inside the root or escaping into the soil to commence feeding elsewhere. These infective nematodes are capable of surviving in moist soil for about three months. In dry conditions they persist for no more than a few weeks.

1147 . Galls of northern root-knot nematode (Meloidogyne hapla).

Principal Characteristics of Pathogenic Agents and Methods of Control

▪ Other viruses transmitted by thrips

Viruses Symptoms and mode of transmission Shape of particles Principal characteristics
Groundnut ringspot virus (GRSV)
Tospovirus
Mottling and mosaic on young leaflets.
Frankliniella occidentalis, F. schultzei.
Identical in morphology to those of INSV. GRSV originated in Africa where in 1996 it was found on Arachis hypogea. It is present in South Africa, Argentina, and Brazil, where it causes symptoms as severe as those of TSWV.
In addition to Arachis hypogea, it infects peppers, tomatoes, and coriander.
Control methods are as recommended for TSWV, Description 43. Note that the ‘Sw-5’ gene in tomato confers resistance to GRSV by hypersensitivity.
Impatiens necrotic spotvirus (INSV)
Tospovirus
Spots and brown, inter-veinal necrotic lesions.
Frankliniella occidentalis, F. fusca.
Spherical or oval virus particles, with a diameter 70–120 nm. INSV was reported for the first time in 1987 on Impatiens sp. growing in the US. It was thought to be a strain of TSWV but is now known to be different and distinct. It spread rapidly from California to several countries in the Americas, including Canada, Mexico, and Costa Rica. It reached the Netherlands in 1989 and was found in several European countries. It affects lettuce and chicory.
This virus has a wide host range especially on ornamentals in glasshouses (Ranunculus sp., cyclamen, Gloxinia speciosa). In addition to tomatoes, it can also infect pepper, tobacco, eggplant, and other Solanum spp., as well as many plants belonging to other botanical families.
Control methods are as recommended for TSWV, Description 43. Note that the TSWV resistance genes used in tomatoes are effective against INSV.
Parietaria mottle virus (PMoV)
Ilarvirus
Spots, necrosis mostly at the base of the leaflets. Longitudinal necrotic lesions on stems, and death of terminal bud.
Chlorotic rings on fruits browning later, becoming corky and causing their deformation.
TI12 strain isolated in Italy causes stunting in plants.
Probably transmitted by thrips.
Isometric particles, nonenveloped, with a variable diameter (24, 29, or 36 nm). Symptoms were first observed in 1972 on tomato in Italy on Parietaria officinalis but the virus was not described until 1987. It spread thoroughout Italy and then to southeastern France and Greece in the late 1990s. Tomato strains are different strains from those that affect Parietaria.
PMoV affect the two hosts mentioned above.
Control methods are as recommended for TSWV, Description 43.
Tobacco streak virus (TSV)
Ilarvirus
Spots, chlorotic rings on leaflets becoming progressively necrotic, particularly near the veins. Necrotic streaks are visible on the stem, they extend to the branches.
The flowers also become necrotic and may fall. The fruits are sometimes covered with necrotic rings.
Thrips tabaci, Frankliniella spp.
It is also transmitted by seeds in beans and several weeds such as Datura stramonium, Chenopodium quinoa, Melilotus alba.
Mechanical transmission via contaminated pollen and thrips.
Isometric not enveloped, with a diameter of 26–35 nm. Globally widespread, it naturally or experimentally infects many hosts such as cotton, tomatoes, asparagus, beans, soybeans, grapes, strawberries, alfalfa, tobacco, ornamental plants (Dahlia spp., Rosa setigera, gladiolus). It can be found on several other plants (Chenopodium quinoa, Datura stramonium) that surround tomato crops encouraging epidemics.
Control methods are as recommended for TSWV, Description 43.
Tomato chlorotic spot virus (TCSV)
Tospovirus
Chlorotic spots on leaflets. Reduced yields.
Frankliniella occidentalis, F. fusca.
Morphology of the virus particles is similar to that of INSV. This virus was discovered on tomatoes in Brazil in 1989. It is now present in Argentina.
In addition to tomatoes, it has been found affecting peppers.
Control methods are as recommended for TSWV, Description 43. Note that the TSWV resistance genes used on tomatoes are effective against TCSV.

ORGANIC SOILLESS MEDIA COMPONENTS

MICHAEL MAHER, . MICHAEL RAVIV, in Soilless Culture , 2008

11.2.3 NUTRITION IN PEAT

The low pH and very low basic level of fertility of peat requires the addition of lime and nutrients to support good plant growth. The amount of nutrients needed depends on the species being grown and the stage of development. Seeding and propagation require only a low level of nutrients, greater amounts are required for rapidly growing plants. Table 11.6 shows additions of lime and N, P and K recommended by various scientists. These rates should be taken as indicative for general purpose mixes for growing plants in pots, different rates would be ideal for different purposes. Thus for seed sowing and for growing salt-sensitive plants, lower rates would be recommended. Traditionally recommendations for additions of N have been for around 200 mg/L, of which at least 50 per cent is in the form of nitrate ( Schrock and Goldsberry, 1982 ), for general purpose growing media. In general, these fertilizer additions are in water-soluble form such as ammonium nitrate, superphosphate and potassium sulphate. Through the life of a pot plant, depending on the length of the cultivation period, supplementary feeding will be necessary to maintain plant growth. The base levels in Table 11.6 should maintain satisfactory growth of many seedlings for 4–5 weeks. If supplementary feeding is given earlier, then the base dressing can be reduced accordingly.

TABLE 11.6 . Recommendations by Researchers in a Number of Countries for Base Levels of Fertilizer and Lime Addition to Peat Based Mixes

Country Dolomitic lime (kg m −3 ) N (g m −3 ) P (g m −3 ) K (g m −3 ) Reference
Finland 8.0 110 105 182 Puustjarvi (1973)
Germany 2.0–5.0 180 80 200 Penningsfeld (1962)
Ireland 5.6 192 112 294 Gallagher (1975)
Netherlands 7.0 120 62 199 Klapwijk and Mostert (1992)
UK 2.25 230 120 290 Bunt (1988)
USA 5.0 192 143 317 White (1974)

Lime is most commonly applied as dolomitic lime which contains both Ca and Mg. Some formulae use ground limestone but then Mg must be added separately, often in the form of magnesium sulphate (kieserite or epsom salts). The rate of lime varies widely as this is influenced by the peat type and the species to be grown. Mixes designed for calcifuge plants such as Azalea would receive a dressing of 1–1.5 kg m −3 ( Maher et al., 2000)

Penningsfeld and Kurzmann (1966) classified various ornamental plants according to nutrient requirement and susceptibility to salt levels and varied his nutrient additions as follows:

Salt-sensitive plants (fertilized at 30–60 per cent of that shown in Table 11.6 )

Pot plants: Adiantum, Anthurium scherzerianum, Asparagus plumosus, Camellia, Erica gracilis, Gardenia, orchid, Primula obconica, Rhododendron simsii.

Bedding plants: Aquilegia, Begonia semperflorens, Callistephus, Dianthus hedwigii, Godetia, Verbena.

Propagation: As seedling compost and for rooting cuttings.

Moderately sensitive plants (fertilized as shown in Table 11.6 )

Pot plants: Aechmea fasciata, Anenome, Anthurium andreanum, Aphelandra squalosa, Cyclamen, Euphorbia fulgens, Freesia, Gerbera, Gloxinia , Hydrangea, Monstera, rose (Rosa spp.), Sanservia, sweetpea (Lathyrus odoratus), Vriesia splendens.

Bedding plants: Campanula, Medium, Dianthus, Matricaria, Penstemon, Petunia, Salpiglossis, Sweet William (Dianthus barbatus), Tagetes, wallflower (Cheiranthus allionii), Zinnia.

Salt tolerant plants(fertilized at 200 per cent as shown in Table 11.6 )

Pot plants: Asparagus sprengeri, Chrysanthemum, Pelargonium, poinsettia (Euphorbia pulcherrima), Saintpaulia.

Micronutrients must also be added to peat-based mixes. These can be added as individual inorganic salts, as components of compound fertilizers or in slow-release form, for example as fritted trace elements (FTE). For example, in Gallagher (1975) the trace elements are applied as follows; B–1.0 g m −3 as Borax, Cu-3.5 g m −3 as copper sulphate, Mn-3.5 g m −3 as manganese sulphate, Zn-3.2 g m −3 , Mo–1.2 g m −3 Fe-7.0 g m −3 as ferrous sulphate and 2.5 g m −3 as iron chelate (EDTA). Alternatively these could be substituted by fritted trace elements (FTE 253A) applied at 400 g m −3 . The advantages of the fritted form are greater convenience, fewer problems in ensuring good uniformity during mixing and potentially greater persistence. The disadvantage is that of greater expense.

The rate of macronutrient addition prior to planting must also be adjusted to account for any supply of nutrients during production in the form of liquid feed. In many cases, an initial low rate of nutrients applied as base dressing will maintain adequate growth for a short period. As this begins to be depleted, liquid feeds must be used to supply nutrients for plant growth. This gives the grower more control over the rate of growth and is particularly important in the raising of vegetable seedlings for transplanting. Growing media marketed to the non-professional market, where the use of liquid feeds is not as developed, tend to have higher levels of nutrients in the media. This promotes active plant growth over a longer period where liquid feed is not given.

Controlled release fertilizers (CRFs) consist of prills of inorganic fertilizers coated with resin or polymers. Water enters the prill through small pores in the coating and the nutrients dissolve and diffuse outwards into the substrate solution. The rate of release of nutrient from the capsules depends on the thickness of the coating, the number of pores, the formulation of the fertilizer compounds inside the prill and the temperature. They are formulated to release nutrients over periods from 3–4 months to over 2 years with the approximate release characteristics described on the product label. CRFs allow the grower to apply sufficient nutrients for the life of the crop as an initial base dressing without the danger of high salt levels occurring as long as the temperatures are relatively moderate and the prills are not damaged. They thus simplify crop fertilization as the crop needs to only be irrigated with water. Their adoption has been greatest in the hardy nursery stock industry where their use has facilitated the development of containerized production of shrubs at the expense of field production. Producers of crops under protection with greater capacity to use liquid feeding have not adopted them to the same extent deterred by their increased cost and the greater control over plant development that liquid feeding affords growers.

Recent advances on interactions between the whitefly Bemisia tabaci and begomoviruses, with emphasis on Tomato yellow leaf curl virus

Pakkianathan Britto Cathrin, Murad Ghanim, in Plant Virus–Host Interaction , 2014

The whitefly Bemisia tabaci—pest and vector status

Nomenclature and host range

The genus Bemisia comprises 37 species and originated in Asia ( Mound & Halsey 1978 ). B. tabaci was first described by Gennadius on poinsettia plants in 1889 as Aleyrodes tabaci and it was described under numerous names before its morphologic variability was recognized. Five distinct groups of B. tabaci have now been identified by comparing their 16S ribosomal subunits. These are: (1) New World (US, Mexico, Puerto Rico), (2) Southeast Asia (Thailand, Malaysia), (3) Mediterranean basin (Southwest Europe, North Africa, Middle East), (4) Indian subcontinent (India, Pakistan, Nepal), (5) Equatorial Africa (Cameroon, Mozambique, Uganda, and Zambia).

First reports of a newly evolved biotype of B. tabaci, the B biotype, appeared in the mid-1980s ( Brown et al 1995b ). Commonly referred to as the silverleaf whitefly or poinsettia strain, the B biotype has been shown to be highly polyphagous and almost twice as fecund as previously recorded strains; it has also been documented as being a separate species, B. argentifolii ( Bellows et al 1994 ). The B biotype is able to cause phytotoxic disorders in certain plant species, e.g. silverleafing in squashes (Cucurbita sp.), and this permits an irrefutable method of identification ( Bedford et al 1992, 1994a ). A distinctive non-specific esterase banding pattern is also helpful in the identification ( Brown et al 1995a ), but it is not infallible ( Byrne et al 1995 ). Based on these markers, the B biotype was reported to spread rapidly ( Costa et al 1993 ). Several ‘biotypes’ were described based on esterase morphotypes.

The Q biotype of B. tabaci was first described as native to the Mediterranean Basin in 1997 ( Guirao et al 1997 ). A closely related Q was also described in Israel in 2005 ( Horowitz et al 2003, 2005 ) and another Q was introduced into the United States in 2005, although it was still confined to greenhouses ( Mckenzie et al 2009 ).

B. tabaci was known mainly as a pest of field crops in tropical and sub-tropical and temperate countries: cassava (Manihot esculenta), cotton (Gossypium), sweet potatoes (Ipomoea batatas), tobacco (Nicotiana) and tomatoes (Lycopersicon esculentum). Its host plant range within any particular region was small, yet B. tabaci had a composite range of around 300 plant species within 63 families ( Mound & Halsey 1978 ).

With the evolution of the highly polyphagous B biotype, B. tabaci has now become a pest of glasshouse crops in many parts of the world, especially Capsicum, squashes (Cucurbita pepo), cucumbers (Cucumis sativus), Hibiscus, Gerbera, Gloxinia , lettuces (Lactuca sativa), poinsettia (Euphorbia pulcherrima) and tomatoes (Lycopersicon esculentum). B. tabaci moves readily from one host species to another and is estimated as having a host range of around 900 species (Asteraceae, Brassicaceae, Convolvulaceae, Cucurbitaceae, Euphorbiaceae, Fabaceae, Malvaceae, Solanaceae, etc.).

Life cycle

Eggs are laid usually in circular groups, on the underside of the leaves. They are anchored by a pedicel which is inserted into a fine slit made by the female ovipositor in the leaf tissues, and not into stomata, as in the case of many other aleyrodids. Eggs are whitish when first laid but gradually turn brown. Hatching occurs after 5–9 days at 30°C; this depends very much on host species, temperature and humidity ( Sharaf et al 1985 ).

On hatching, the first instar, or ‘crawler’, is flat, oval and scale-like. This first instar is the only larval stage of this insect which is mobile. It moves from the egg site to a suitable feeding location on the lower surface of the leaf where its legs are lost in the ensuing molt and the larva becomes sessile. It does not therefore move again throughout the remaining nymphal stages. The first three nymphal stages last 2–4 days each (this could, however, vary with temperature). The fourth nymphal stage is called the ‘puparium’, and is about 0.7 mm long and lasts about 6 days; it is within the latter period of this stage that the metamorphosis to adult occurs. The adult emerges through a ‘T’-shaped rupture in the skin of the puparium and spreads its wings for several minutes before beginning to powder itself with a waxy secretion from glands on the abdomen. Copulation begins 12–20 hours after emergence and takes place several times throughout the life of the adult. The life span of the female could extend for up to 60 days. The life of the male is generally much shorter, being between 9 and 17 days. Each female lays up to 160 eggs during her lifetime, although the B biotype has been shown to lay twice as many, and each group of eggs is laid in an arc around the female. Eleven to fifteen generations can occur within 1 year.

Significance and symptoms of B. tabaci infestations

B. tabaci has been known as a minor pest of cotton and other tropical or sub-tropical crops in the warmer parts of the world and, until about two decades ago, has been easily controlled by insecticides. In the southern states of the United States in 1991, however, it was estimated to have caused combined losses of 500 million US dollars to the winter vegetable crops ( Perring et al 1993 ) through feeding damage and plant virus transmission. B. tabaci is also a serious pest in greenhouses worldwide. Depending on the level of infestation, the whitefly can cause leaf yellowing, and those leafs are later shed. The honeydew produced by the feeding of the nymphs covers the surface of the leaves and can cause a reduction in photosynthetic potential when colonized by molds. Honeydew can also disfigure flowers and, in the case of cotton, can cause problems in processing the lint. With heavy infestations, plant height, number of internodes and quality and quantity of yield can be affected (e.g. in cotton). The larvae of the B biotype of B. tabaci are unique in their ability to cause phytotoxic responses to many plant and crop species ( Costa et al 1993 ). These include a severe silvering of squash leaves, white stems in pumpkin, white streaking in leafy brassica crops, uneven ripening of tomato fruits, reduced growth, yellowing and stem blanching in lettuce and kai choy (Brassica campestris) and yellow veining in carrots and Lonicera ( Bedford et al 1994a,b ).

The significance of B. tabaci as a virus vector

B. tabaci is the vector of over 100 plant viruses in the genera Geminivirus, Closterovirus, Nepovirus, Carlavirus, Potyvirus and a rod-shaped DNA virus ( Markham et al 1994 ). The geminiviruses are by far the most important viruses agriculturally, causing yield losses to crops between 20 and 100% ( Brown & Bird 1992 ). Geminiviruses cause a range of different symptoms which include yellow mosaics, yellow veining, leaf curling, stunting and vein thickening. Estimates indicated that a million ha of cotton is being decimated in Pakistan by the Cotton leaf curl virus (CoLCV) ( Mansoor et al 1993 ), and important African subsistence crops such as cassava are affected by disastrous geminiviruses such as the African cassava mosaic virus (ACMV). Tomato crops throughout the world are particularly susceptible to many different geminiviruses, and in most cases they exhibit yellow leaf curl symptoms. Most of these epidemics in the Old World are attributed to Tomato yellow leaf curl virus (TYLCV) but may also be caused by other geminiviruses. TYLCV has also been recorded in the New World, but several others, exclusively American, tomato geminiviruses have now been described, e.g. Tomato mottle virus ( EPPO/CABI, 1996 ).

The emergence of the B biotype of B. tabaci, with its ability to feed on many different host plants, has given whitefly-transmitted viruses the potential to infect new plant species. Two viruses have been shown to be no longer transmissible by B. tabaciTobacco leaf curl virus (TLCV) and Abutilon mosaic virus (AbMV)—possibly through many years of vegetative propagation of their ornamental host plants ( Bedford et al 1994a ). The major virus transmitted by B. tabaci is TYLCV that is causing major crop losses within the tomato industries of Spain, Italy, Israel and recently China and the United States. Newly identified B. tabaci-transmitted closteroviruses are reported to cause severe damage to cucumbers and melons in Spain and other Mediterranean countries ( Berdiales et al 1999 ).

During this long-lasting virus–vector relationship, begomoviruses might have optimized the conformation of their capsid to fit the receptors that mediate their circulation in the insect host and to interact with insect proteins. It is interesting to note that the adaptation of the local vector to the local begomovirus is reflected in the parameters of acquisition and transmission. Transmission of a begomovirus by B. tabaci from the same geographic region is more efficient than in the case where the virus and the insect originated from two different regions ( McGrath & Harrison 1995 ), suggesting an adaptation between the viruses and their vectors in the same geographic area. Circulation of begomoviruses inside their whitefly vectors may be one mechanism developed to avoid the invasion of insect tissues by harmful viruses. In the latter case, it is clear that these efforts have been only partially successful because many begomoviruses remain associated with the insect vector for many days following a short acquisition access period (AAP) ( Polston et al 1990 , Caciagli et al 1995 , Rubinstein & Czosnek 1997 ), and some begomoviruses are able to invade the reproductive system ( Ghanim et al 1998 , Bosco et al 2004 , Wang et al 2010 ) and affect vital parameters ( Rubinstein & Czosnek 1997 , Jiu et al 2007 , Matsuura & Hoshino 2009 ).

www.sciencedirect.com

Share:
No comments

Добавить комментарий

Your e-mail will not be published. All fields are required.