Overview
Many insect and mites attack trees in Asia. Although some affect production in nearly all locations, many others are of only local significance. Relatively few species cause significant crop loss in their own right, and are only a problem when the population exceeds damaging thresholds. The less important species may at times require special attention, especially if their natural enemies have been disrupted by chemical sprays.
There are a few diseases affecting leaves, flowers and fruit, and some others causing tree deaths or decline. However, no major disease currently limits production in the Region. Brown blight (Peronophythora litchii) infects leaves, panicles and fruit in China and Thailand, but can be controlled with metalaxyl. Anthracnose (Colletotrichum gloeosporoides) and similar diseases also attack fruit in China, India and Australia. Parasitic algae and nematodes affect some orchards, but can be readily controlled with available chemicals. Various organisms have been associated with tree deaths or decline in Asia and Australia, although their pathogenicity is yet to be proven.
Regardless of where lychee is grown, several insect groups attack the flowers, fruit, leaves and branches. Lepidopterous fruit borers are generally the most important pests affecting production. Other important species include various leaf- and flower-eating caterpillars and beetles, bark borers, scales, leaf mites, fruit-sucking bugs, fruit-piercing moths and fruit flies.
7.1.1 Fruit borers
Conopomorpha sinensis Bradley, known as the lychee stem-end borer in China and the lychee fruit borer in Thailand, is the major pest in most seasons. This pest was previously recorded as Acrocercops cramerella (now Conopomorpha cramerella Snellen). C. sinensis and the related C. litchiella Bradley both attack lychee, the latter preferring leaves and shoots, while C. cramerella is restricted to rambutan and cocoa (Bradley, 1986).
C. sinensis lays yellow, scale-like eggs 0.4 x 0.2 mm long on the fruit any time after flowering, as well as on new leaves and shoots. Both lychee and longan are affected. The eggs hatch in three to five days, with the larva immediately penetrating the fruit, leaf or shoot. They tunnel through the flesh of the fruit that often fall from the tree.
In Thailand, fruit are inspected weekly from fruit set to detect eggs of C. sinensis, which are very small and almost invisible to the naked eye. Infested fruit should be picked and destroyed, at infestation levels of 1 to 2 percent. When the pest becomes more active, permethrin is applied weekly, up to two weeks before harvest. In Taiwan Province of China, cypermethrin, deltamethrin, carbofuran or fenthion during early fruit set is recommended to prevent damage later in the season. Moths can be excluded by enclosing the fruit panicles in nylon mesh bags, but is uneconomic in areas with high labour costs. If the parasitoids Phanerotoma sp. and Apanteles sp. are not active, fallen fruit should be removed to reduce the build-up of moths.
All stages of the leaf-miner, Conopomorpha litchiella Bradley, are similar to those of the fruit borer. The female lays its eggs on new shoots and the small, light-yellow eggs hatch three to five days later. The newly hatched larva is creamy white, and bores into shoots and leaf blades, usually into the mid-rib and veins. The moths are attracted to leaf flushes that emerge during the rainy season from June to October in Thailand. Affected shoots often wilt.
Bearing trees should be inspected during early flush development and sprayed if necessary. The leaf flush before flower initiation is very important as it supplies the carbohydrates needed for fruit development. If 30 to 40 percent of the larvae are parasitised, spraying is not recommended. Young, non-bearing trees do not need to be sprayed either. This also allows the parasitoids to build up in the orchard.
The insect originally referred to as Argyroploce illepida Butler (= Cryptophlebia carpophaga Walsingham) in India (Butani, 1977), is actually Cryptophlebia ombrodelta Lower (Bradley, 1953). It also occurs in Thailand, China, Japan, Taiwan Province of China and Australia, but only in the latter area is it regarded as a significant pest.
The creamy white eggs of these species are oval and flat with a reticulate surface, and are about 1.0 x 0.8 mm. They are laid singly or in groups of up to 15 on the fruit surface. The newly hatched larva feeds on the fruit skin and then tunnels towards the seed. In immature fruit, the young larva bores directly into the seed, which is completely eaten. A single larva may damage two or three fruit, if the fruit are small. However, they prefer mature colouring fruit with larger seeds.
In South Africa, the insect growth regulator, triflumuron as a single, full cover spray 40 days before harvest, or two sprays of teflubenzuron a fortnight apart commencing when the fruit are 10 mm in diameter, are recommended. Alternatively, the panicles can be covered with paper bags. The bags also improve fruit colour and overall quality. In Queensland, carbaryl and azinphos-methyl have been used with varying success. Several sprays commencing at fruit colouring are applied on a calendar basis, with monitoring for the presence of eggs less common. Newer insecticides including the insect growth regulator, tebufenozide, provide better control, with less disruption to natural enemies.
The various species of Cryptophlebia are attacked by their own complex of egg, larval and pupal parasitoids; however, these do not always keep borers below economic thresholds. Egg parasitoids such as Trichogrammatoidea fulva Nagaraja from India and T. cryptophlebiae from South Africa and Australia, offer the best prospects for biological control.
7.1.2 Fruit-piercing moths
Fruit-piercing moths such as Eudocima (Othreis) fullonia (Clerck), Eudocima salaminia (Cramer) and Eudocima jordani (Holland) are important throughout Asia, Australia and the South Pacific. The larvae of these moths develop on a variety of host plants such as the coral tree, Erythrina, and vines of the Menispermaceae (Legnephora, Stephania, Fawcettia, Tinospora, Carronia, Sarcopetalum, Pleogyne and Hypserpa).
The moths have a proboscis that drills a neat hole in the skin of the fruit allowing them to suck the juice from the flesh. Contamination of the wound with yeasts and bacteria carried on the proboscis destroys the fruit. Drosophila spp. attracted to the fermenting juice hastens deterioration. Within a few days, a frothy exudate seeps from the fruit and stains undamaged fruit close by. In Australia and Thailand, farmers go to their orchards at night with spotlights and attempt to catch the moths. However, this is futile.
Australian farmers also make traps by draping shade cloth loosely over a frame of wire and baiting it with fermenting citrus and bananas. The moths feed on the fruit and become entangled in the folds of the shade cloth when they attempt to fly off. Several traps are required to protect an orchard and even then, substantial damage is sustained. In Thailand, ripe bananas and pineapples are dipped in insecticide and hung in the trees to poison the feeding moths. In some countries, panicles are covered with paper bags. In recent times, parrots and fruit bats have become a severe problem for growers in Australia. Fine nets erected over the orchard control fruit-piercing moths as well as the vertebrate pests.
7.1.3 Leaf-feeding caterpillars
Oxyodes scrobiculata F. and Oxyodes tricolor Guen. occupy similar niches in Thailand and Australia. In Australia, O. tricolor attacks trees in southern Queensland, but is not a pest in the north. The castor oil looper, Achaea janata (L.), is a voracious feeder in Australia and often infests trees in large numbers at the same time as O. tricolor. The caterpillars can cause severe defoliation.
In Thailand it is recommended that carbaryl be applied when there are two to three young larvae per leaflet. Shaking the tree to dislodge larvae onto the ground improves the effectiveness of the sprays. If 40 percent or more of larvae are parasitised, sprays should not be necessary. In Australia, Bacillus thuringiensis Berliner (Bt), endosulfan or methomyl may be used when damaging populations of O. tricolor appear.
7.1.4 Leafrollers
Olethreutes perdulata Meyr. is an occasional pest in Queensland. Platypeplus aprobola (Meyrick) has also been recorded in Australia, China and India. Adoxophyes cyrtosema Meyr. and Homona coffearia Nietner attack trees in Guangzhou and Fujian. The latter species along with Homona difficilis is recorded in lychee, longan and rambutan in Thailand. The orange fruit borer, Isotenes miserana (Walker), is another leafroller that also attacks flowers and fruit in Queensland.
P. aprobola is a minor pest in China and India where it attacks leaves and flowers. However in Australia, it is part of a complex of species contributing to a significant loss of flowers. In China, A. cyrtosema and H. coffearia also feed on leaves, flowers and fruit.
In Australia, the damage caused by leafrollers is tolerated so long as it is restricted to the foliage and unlikely to affect flower initiation. If necessary, methomyl or carbaryl can be applied when 20 percent of leaf flushes are infested, to minimize damage to young trees or at critical periods of leaf growth in older trees. In India, rolled leaves that contain larvae are removed manually during light infestations, but phosphamidon, fenitrothion or endosulfan are applied for heavy infestations.
7.1.5 Beetle borers
The longicorn beetle, Aristobia testudo (Voet), is a serious pest of lychee and longan in Guangdong (Zhang, 1997). The beetle has one generation per year, with adults emerging from June to August. The females girdle branches by chewing off 10 mm strips of bark, with the eggs laid on the wound and covered with exudate. The larvae hatch from late August and live under the bark until January when they bore into the xylem and create tunnels up 60 cm long. In Taiwan Province of China, the white-spotted longicorn beetle, Anoplophora maculata (Thomson), has a one-year life cycle. Adults emerge in spring and females insert about twenty eggs individually into T-shaped incisions in the bark, 0.5 m above the soil surface. The larval period lasts about ten months. In Australia, the longicorn beetle, Uracanthus cryptophagus, causes similar damage (Plate 7).
Tunnelling by the larvae may kill branches, but rarely whole trees. Ring-barking of twigs by ovipositing adults causes the shoot tips to die and snap off. In China, regular inspections of trees during adult activity enable orchard workers to remove the beetles. Eggs and young larvae can also be removed at the same time. Established larvae can be located from the appearance of their frass, which is packed into the ends of tunnels. They can then be 'fished out' with wire hooks and knives. Alternatively, dichlorvos is injected and the tunnels sealed with clay (Zhang, 1997).
7.1.6 Scarab beetles
The elephant beetle, Xylotrupes gideon (Linnaeus), is important in all areas of Australia. The larvae develop in the soil or mulch where they feed on plant roots and humus. The large, heavily-sclerotised and sexually-dimorphic adults emerge in spring. Later, they are attracted to the fruit as they ripen, especially those that have split or been damaged by parrots and fruit bats. They then start attacking sound fruit and can cause significant economic losses in the week or so leading up to harvest. Chemical control is unsatisfactory. Manual removal is effective in small trees, but difficult in large trees. Labour is relatively expensive in Australia, so this operation adds significantly to growing costs.
7.1.7 Soft scales
Pulvinaria (Chlorpulvinaria) psidii (Maskell), the green shield scale, infests trees in China, Taiwan Province of China, Australia and India. In Queensland, crawlers are produced in spring by adult scales that infest the leaves and twigs. Some of these crawlers move onto the flowers and young fruit. The female scales are sometimes mistaken for mealybugs because the egg masses that are covered in waxy filaments cover the ends of the scale.
Soft brown scale, Coccus hesperidum Linnaeus, is an occasional pest in Queensland, where chemicals have disrupted its parasitoids or it is protected by ants. Parasaissetia nigra (Nietner) and Saissetia coffeae (Walker) infest trees in India along with C. psidii, but they are not important.
These scales cause no damage as they feed, but the fruit become unmarketable when significant populations develop on the surface, as they often do in China, Taiwan Province of China and Australia. The scales also produce honeydew, which supports the growth of sooty mould on infested fruit and panicles, and those below. These discoloured fruit are downgraded or rejected in the market-place.
Severe infestations may be controlled with methidathion, although applications of mineral oil are preferred so that effective predators, the mealybug ladybird, Cryptolaemus montrouzieri Mulsant, and the green lacewing, Mallada signata (Shneider) are not affected.
7.1.8 Bugs
Several bugs belonging to Tessaritomidae attack lychee and longan throughout Asia and Australia. Tessaritoma papillosa Drury occurs in southern China, Vietnam, Thailand, Myanmar, the Philippines and India, although Butani (1977) notes that Tessaritoma javanica Thunberg and Tessaritoma quadrata Distant, are the main species in India. In Australia, Lyramorpha rosea Westw. is known as the lychee stink bug, but rarely causes damage.
In China, T. papillosa has one generation per year. Adults tend to aggregate and over-winter mostly on lychee and longan, but may also be found on other hosts in warm protected areas. In spring, the females are attracted to trees with new flowers and shoots. They mate and lay up to 14 egg masses, each containing about 14 eggs, on the back of leaves. Peak egg-laying occurs in March in Guangdong, but continues through to September. The first nymphs mature in June, while there are still old adults in the trees. These old adults may have lived for up to a year, and generally die by August. The new adults do not mate immediately, but mature over winter and mate and lay eggs the following spring.
Adults and nymphs feed on terminals, which may be killed, and also on flowers and fruit, causing these to fall. Liu and Lai (1998) claimed that up to 30 percent of fruit in commercial orchards are damaged despite chemical applications.
In Guangdong, the main natural enemies are the egg parasitoids, Encyrtus (Ooencyrtus) sp., Anastatus sp. and Blastophaga sp. which parasitise 70 to 90 percent of eggs laid late in the season. Similar results were recorded by Liu and Lai (1998) when parasitised egg cards were hung in trees during March. In orchards under integrated pest management, combined parasitism rates by Anastatus sp. and Ooencytus sp. may reach 50 percent in June, but may be less than 3 percent in orchards that rely on chemicals. During the 1970s, biological control in Guangdong was initiated using the egg parasitoid Anastatus japonicus Ashmead, the flat venter wasp, after field trials had demonstrated its value. Since only 10 percent of eggs are parasitised by April when most of the eggs are laid, natural control is ineffective. In contrast, very good control with up to 90 percent parasitism is achieved after mass release of wasps.
In Thailand, the egg parasitoids Anastatus sp. nr. japonicus and Ooencrytus phongi, operate in a similar manner to their counterparts in China. Low levels of control are achieved during the critical early fruit production period, building up to good levels later. Mass rearing of the parasitoids in the wild silk worm, Philosamia ricini Hutt., and releasing them early, produced results similar to those in China. Anastatus sp. and O. phongi parasitised 79 percent and 21 percent of eggs, respectively (Nanta, 1992).
If chemicals are used, the timing of sprays is critical because the bugs vary in their susceptibility to trichlorfon at different times of the year, depending on body fat content and its nature.
Amblypelta nitida Stål, the fruitspotting bug, and Amblypelta lutescens lutescens (Distant), the banana spotting bug, are major pests of tropical fruit in Queensland (Waite, 1990). The adults over-winter on citrus or non-crop native or exotic ornamentals, and start to move into lychee and longan orchards in spring when the trees flower. They prefer to feed on green fruit, and so are very common just after fruit set. Orchards near rainforests where the bugs breed are particularly susceptible (Waite and Huwer, 1998).
The bugs feed on the developing seed and this causes the fruit to fall a couple of days later. The puncture mark is invisible on the fruit surface and the only way to distinguish damage from natural drop is to dissect the fruit. Fruit that has been attacked typically have a tan lesion on the seed testa. Endosulfan should be applied if more than 10 percent of fallen fruit have been stung. Usually, a maximum of two sprays applied two weeks apart, during the first six weeks after fruit set is sufficient.
7.1.9 Mites
Erinose mite, Aceria litchii (Keiffer), also known as hairy mite, hairy spider, or dog ear mite, occurs throughout China, Taiwan Province of China, India, Pakistan and Australia. Females lay eggs singly on the leaf surface amongst the erineum induced by their feeding. The eggs are only 0.032 mm in diameter, spherical and translucent white. The mites are also small, only 0.13mm long and pinkish-white. All stages have only four legs, but are quite mobile and move easily from old leaves to infest new flushes. Their feeding stimulates the production of the erineum where they shelter and feed. Numbers vary with the cycle of shoot growth, and are highest in summer and lowest in winter. Planting material obtained as marcots may be infested if they have been taken from trees with the mites. Later infestations occur when the mites are moved around the orchard by direct contact between trees, or carried around by orchard workers, wind and bees (Waite and McAlpine, 1992).
The mites attack new leaves causing a felt-like erineum to be produced on the under-surface. This forms as small blisters but may eventually covers the entire leaf, causing it to curl. In severe cases, whole terminals may be deformed. The young erineum is silver-white, changing to light brown and dark reddish-brown, and eventually black. The greatest numbers of mites are found in the intermediate stages.
Many leaves are ruined if infestations are severe (Plate 8). This generally causes no problems in established trees, but can debilitate young orchards. There can also be a problem if the mite moves from leaves onto the developing flowers and fruit. Fruit set can be disrupted or the fruit deformed. Such fruit are unmarketable.
Numerous species of predatory mites, particularly those from the Phytoseidae, have been recorded with A. litchii (Wu et al., 1991; Waite and Gerson, 1994). Agistemus exsertus Gonzalez (Stigmaeidae), has been used for control in Guangdong, Guangxi and Fujian.
Branches infested with the mite should be cut off and burnt. The mites can be controlled by applying insecticides when they move from the older leaves to a new flush. The leaves should be checked regularly for symptoms over summer and autumn. Not all trees in an orchard will be flushing or infested at the same time. In Australia, three sprays of dimethoate or wettable sulphur every two to three week during leaf emergence and expansion generally provide adequate control. Chemicals recommended in China include dichlorvos, dimethoate, dicofol, chlorpyrifos, omethoate and isocarbophos (Zhang, 1997).
7.1.10 Gall flies
The leaf midge, Dasyneura sp., is a major pest in China (Zhang, 1997). Litchiomyia chinensis Yang and Luo was described from specimens reared from galls on lychee leaves collected in Guangdong. The larvae over-winter in the galls produced as a result of their feeding. They pupate in the soil, with the adult flies initiating the first of eight overlapping generations from March. The midges prefer damp, closed canopies and dry out in exposed areas. The adults lay eggs in lines on young leaves. The larvae then mine the leaf, causing 'watery dots' that later become the “galls”. These turn brown and eventually drop out, giving the leaf a “shot-hole” appearance.
In susceptible orchards, monitoring is not effective and preventive procedures are required. As with erinose mite, infested leaves can be removed after harvest and burnt. Later in the spring, methyl parathion (2.5 percent) at 75 kg per ha can be distributed under the trees, or isofenphos (0.001 percent) can be sprayed on the ground just prior to emergence of the adults. In autumn, isocarbophos (0.001 percent) should be sprayed twice over two weeks during early leaf development (Zhang, 1997).
7.1.11 Fruit flies
In Queensland, Bactrocera tryoni (Froggatt) occasionally attacks lychee, but is not considered economically significant. Females lay their eggs through the skin of the fruit, often utilizing cracks and wounds made by other pests. Although the eggs can hatch, the larvae rarely survive (de Villiers, 1992), probably because of the juice in mature fruit drowns them. The flies in Queensland, and related species in Africa and Hawaii, are capable of ovipositing through the skin of lychee, although some cultivars may be too thick. The only real fly problem appears to be in South Africa, with Ceratatis rosa. However, the level of damage is still quite low. In South Africa, pheromone-baited traps can be used for monitoring populations. Control is achieved with bait sprays of protein hydrolysate mixed with trichlorfon or mercaptothion. Alternatively, the panicles can be covered with paper bags after the November fruit drop.
No major disease currently limits commercial production in Asia. Diseases are more important after harvest, although undoubtedly many of the fruit are infected before picking. There are a few organisms that infect the leaves, flowers and fruit, and a few others associated with tree decline and tree deaths. Chemicals are generally available for controlling diseases on the flowers and fruit. In contrast, more efforts need to be made to control the loss of trees.
7.2.1 Brown blight
Brown blight, Peronophythora litchii, is a major disease in both lychee and longan in China and Thailand, although more important in the former. It is also reported to affect lychee in India. It is well described in Guangdong, and attacks leaves and panicles, as well as fruit that can be infected right up to harvest. These infections all reduce production and shelf life. Flower panicles are particularly susceptible. Immature fruit turn brown, while those infected before harvest have a white mildew growing on the skin.
The fungus over-winters in the soil or on old infected fruit, with the spores spread by wind, rain and insects. Continuous wet weather and temperatures of 22° to 25°C favour infection. It is suggested that growers clean up their orchard by removing shaded, infected and dead branches after harvest. Copper oxychloride during winter and copper sulphate in spring also help to reduce inoculum levels. These chemicals are replaced by fosetyl-Al or metalaxyl during flowering and fruit development.
7.2.2 Anthracnose
Anthracnose, Colletotrichum gloeosporoides, is a major disease in Guangdong, and also occurs in India. Although it attacks leaves and branches, along with flowers and flower stalks, infected fruit are unmarketable. Lesions on the leaves may appear as small round light grey areas, or irregular brown marks at the tips. In contrast, infections are much more obvious on the flowers and fruit. Outbreaks are common after warm wet weather. The fungus may not always cause immediate disease, which sometimes only becomes apparent after harvest. Fungicides are used during an initial outbreak, but are not always effective.
A form of anthracnose caused by Colletotrichum gloeosporioides (Glomerella cingulata in the sexual state) also affects trees in Australia. Pepper spot causes superficial skin blemishes to the fruit, but does not effect production, fruit quality or shelf life. More than half of the crop may be unmarketable in some orchards. The disease has been recorded on all cultivars, but is most severe on the popular “Kwai May Pink”.
The disease first appears as brown pinhead freckles, usually on the top of semi-mature fruit, in areas with overhanging branches. The spots do not increase in size, but rapidly turn black. More spots appear on the top and sides of the fruit and may, by harvest, cover up to half of the fruit surface. Infections over-winter on the leaves, with the fungus potentially spread from nurseries to new orchards.
Until the appearance of pepper spot, lychee was generally free of diseases affecting fruit or foliage in Australia. However, the occurrence of the disease has resulted in attempts to control it using copper oxychloride and copper hydroxide. Calendar sprays of copper are costly and could lead to unacceptable residues if used close to harvest. Other chemicals such as mancozeb are being evaluated.
7.2.3 Tree decline
A slow decline and a sudden death have been recorded in China, Viet Nam and Australia, especially in poorly drained soils. It can affect the whole tree or just one or two branches. The symptoms include a sudden branch wilt that is followed by the decline of new growth on the affected branch over a period. In other situations, the tips die without wilting. The tree or branch may recover temporarily, but subsequently dies. Parts of the tree flush and grow, while other sections die.
A number of organisms including Phytophthora, Pythium and Fusarium have been isolated from the roots of trees, but it is not known where they cause the disease. A root rot caused by Clitocybe is reported to kill trees in the Philippines. Growers are advised not to plant on waterlogged soils.
Armillaria occasionally attacks roots and the base of trees of any age causing death or slow decline. The fungus may survive in the soil, or on stumps and roots of various trees for many years. The planting sites need to be fumigated before establishing new trees in the orchard.
7.2.4 Parasitic algae and nematodes
A parasitic algae, Cephaleuros virescens, occasionally attacks trees in Australia causing loss of vigour. Cultivars such as “Souey Tung” and “Haak Yip” are very susceptible. It can be controlled with two sprays of copper, before and after the wet season.
Nematodes such as Xiphinema, Paratrichodorus and Helicotylenchus are a problem in South Africa, but whether they are significant in Australia and Asia is not yet clear. Post-plant nematicides are used in South Africa, but have not been evaluated elsewhere.
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