Dracaena marginata

PEST

   NAME

     Mealybugs

     Various Mealybug Species

   ORDER

     Hemiptera

   FAMILY

     Pseudococcidae

Description of the Pest

Adult females are 3-5mm long, flattened oval-shaped white insects, which secrete a white, mealy wax that forms a row of hair-like filaments of fairly uniform length around the edge of the body; the hind end bears one or two pairs of filaments that are longer than the others. They are mobile but slow-moving. The seldom-seen adult males are tiny winged insects with a pair of long waxy tail filaments. Early stage nymphs are tiny, pink and mobile; later stages resemble adult females.

There are many types of mealybugs including;

·        Longtailed Mealybugs (Pseudococcus longispinus) generally have tail filaments that are longer than there body. If squashed yellow body fluid is revealed and the eggs are laid under the body and normally hatch immediately.

·        Citrus Mealybug (Planococcus citri). This insect has tail filaments that are less than 1/3 the length of its body. It produces yellow orange body fluid and lays eggs in a cottony mass.

·        Citrophilous Mealybug ( Pseudococcus calceolariae). This insect has tail filaments that are about 1/3 the length of its body. It produces dark red body fluid and the eggs are laid in a cottony sac.

·        Root Mealybug (Rhizeocus falcifer). This insect is not normally seen but produces a open white mass as it feeds on the outer or terminal roots, normally container plants, particularly cacti species. The eggs are laid in the waxy mass and adults may dispersed by ants.

·        Hibiscus Mealybug (Maconellicoccus hirsutus)

·        Tuber Mealybug (Pseudococcus affinis)

The Mealybugs (Pseudococcus  adonidum) and (Planococcus citri) are a major pest of cacti species,  sucking sap and turning the infected area yellow. These pests are also found on Strelitzia, Camellia and Yucca species.

Appearance and Distribution of the Pest

Mealy bugs are found worldwide. The above ground species are found in sheltered areas such as under a leaf or in leaf bases. They are also found where two fruits or leaves touch and are not readily noticeable.

The below ground species are only found when a plant is re-potted or the infected plant wilts and dies. Mealybugs are distributed several ways including slowly walking to a new host or transferred on clothing, contaminated plants or strong wind and on visiting insects. They are also farmed by ants which in a nursery situation infest pots by tunnelling and carrying mealybugs to the roots.

Attending Ants

Life Cycle

These insects have a Hemimetabolous life cycle, ie. When the immature nymphs resemble the adults.

Up to 200 young are produced in 2-3 weeks; eggs may hatch as they are being laid. The life cycle includes eggs, nymphs (3 to 4 stages) to adult takes 6 weeks, in warmer months; several generations appear throughout the year.

Period of Activity

Active all year, particularly in spring and autumn. Warm, humid conditions are preferred and the insect overwinter outdoors as eggs. These may be found on surrounding weeds. In Citrus species many longtailed mealybugs overwinter as juveniles, maturing during spring. In a Glasshouse conditions mealybugs are active through the year.

Damage Caused

Adults and nymphs suck sap, congregating in sheltered parts of the plants; some species feed undetected on roots. Early infestations may go unnoticed until the plant begins to wilt. The insect also produces honeydew, which gives rise to sooty mould.

         Clivia miniata

Susceptible Plants

Mealybugs are found on a wide variety of trees and shrubs. They are also destructive to many ornamentals; including indoor plants (especially African violets and ferns), and are a major greenhouse pest.

Cactus species

Many species of mealybug are common pest of cactus and succulents.  The small, grey to light brown mealy bugs are difficult to see amongst the spines. Nesting females appear as the small balls of white fluff on cactus spines or around the base and under the rim of the pots.  The female will produce eggs or living nymphs and the insect will produce honeydew that attracts ants.  Ants should be discouraged as they farm mealy bugs, moving them from one place to another in a cactus collection.

Cactus is also attacked by the root mealybugs that infest the roots of plants and their damage allows fungal and bacterial infections to enter the plant tissue.  They can be identified by white fluffy deposits in the soil or underneath a pot and appeared as tiny pinkish brown wood lice up to 3 mm long.

Catalpa species are susceptible to the mealybug (Pseudococcus comstocki) which is a wax covered mealybug that causes distorted growth of the branches and branchlets.

Fern species are commonly attacked by mealy bugs and can be recognised by small white, waxy secretions as it feeds in the crevices at vein junctions or on the exposed rhizome.

Hedera and Crassula species are susceptible to three species of mealybugs including Citrus Mealybug (Planococcus citri) and not normally requiring control.

Laburnum anagyroides is infested with the Grape Mealybug (Pseudococcus maritimus) infesting the branches and twigs.

Plumeria acutifolia becomes infested with mealybugs on the new growth but normally control is not required.

Psidium species are attacked by the Longtailed Mealybugs (Pseudococcus longispinus).

Sequoia species are attacked by three species of Mealybugs including (Planococcus citri).

Thymus species are attacked by the Root Mealybug (Rhizeocus falcifer).

Thuja species Cupressus macrocarpa and Araucaria heterophylla are can be infested with the mealybugs (Pseudococcus ryani).

Turf Grass may be infested with mealybugs causing severs damage and often go undetected and build up large colonies quickly. The turf forms brown dry patches and looks simular to Dollar Spot the infestation may also occur around core holes and can be discouraged by generous watering. Agrostis palustris (Bent) and Cynodon species (Couch) are commonly attacked.

Yucca species are attacked by the mealybug (Planococcus citri).

Cultural Control

Small plants may be sprayed with a soapy water solution or sponged down preferably during the evening. Heavily infected areas should be pruned and destroyed or the whole plant removed. Infested pot-plants should be discarded and thoroughly disinfect pots before recycling). Maintain vigour by watering to replace sap loss, this helps infected plants to recover.

As a preventative measure for root mealybugs grind up mothballs and add them to the potting mix to discourage infestations.  Care should be taken as the chemicals in mothballs can damage plastic pots (use clay pots) and in some countries such as the UK. mothballs must be used as directed on the label.

Biological Control

Lacewing and ladybeetle larvae (Cryptolaemus montrouzeri) control small infestations. This predator insect requires temperatures of at least 21° C. (70°F) and in small infestations it is difficult to maintain a balance between predator and prey.  

Ladybird beetle larvae eats Mealybugs                              Ladybird beetle up to 4 mm long

Chemical Control

Spray with white oil may have an effect on the population or spray Omethoate. Contact insecticides are usually ineffective because of the insect's protective waxy coating.

Note

Always read the label for registration details and direction of use prior to application of any chemicals.

PEST

   NAME

     Fuller's Rose Weevil

     Various Rose Weevil  

Species

   ORDER

     Coleoptera

Description of the Pest

The Fuller's Rose Weevil (Asynychus cervinus) is greyish-brown and grows to 7mm long and is found in Australia. The female adult has faint white marks on its sides and feeds on leaf margins and flower buds. It lays its eggs under loose bark or in curled dead leaves that have fallen to the ground. The light grey lava is up to 6mm long burrow down feeding on the roots, where they overwinter.

The Fuller's Rose Weevil (Pantomorus godmani) female adult is greyish-brown, up to 8mm long with diagonal white stripes across its wing covers and feeds on leaves at night. It is found in northern and southern USA. The lava feed on the roots and overwinters under ground.

Distribution of the Pest

Fuller's Rose Weevil's are found throughout the world and are distributed by walking to a new host or are transported on infested plants.

Life Cycle

These insects have a Holometabolous life cycle, ie. When metamorphosis is observed during the pupal stage.

The adult female can live up to three months during which it can lay up to ten groups of thirty eggs and the lava, can remain under ground for up to nine months before emerging as adults.

Period of Activity

The adult is most active from summer to autumn.

Damage Caused

Generally the adults chew leaves, preferring new foliage or flower buds and on mass can cause sever damage to the host. The roots are attacked by the lava and may cause yellowing of the foliage and small plants such as Lycopersicon species may be killed.

Susceptible Plants

There are many plants that are attacked by these pests, particularly broad leafed types.

Camellia, Citrus, Dahlia, Gardenia, Passiflora, Prunus, Rosa and Rubus species are susceptible to the Fuller's Rose Weevil (Asynychus cervinus).

Acacia, Begonia,  Camellia, Canna, Chrysanthemum, Cissus, Citrus, Dianthus, Diospyros, Dracaena,  Fuchsia, Gardenia, Hibiscus, Lilium, Pelargonium, Penstimon, Plumbago, Prunus persica, Quercus, Rhododendron,  Rosa and Vinca, species.

All are susceptible to attack by the Fuller's Rose Weevil (Pantomorus godmani).

Cultural Control

Small infestations may be removed by hand at the adult stage and fallen leaves or debris should be removed from around the base of the plant. Sticky traps at the base of the plant may inhibit the adult climbing the plant.

Chemical Control

Plants may be sprayed with Carbaryl when the adults are first seen.

Note

Always read the label for registration details and direction of use prior to application of any chemicals.

PEST

   NAME

     Thrips (General)

     Various Thrip Species

   ORDER

     Thysanoptera

Description of the Pest

There are many species of thrips that attack living and dead plant material. The winged adults are black, yellow, white or brown with slender bodies and up to 2mm long. The folded fringed wings appear as silvery stripes and the smaller nymphs are difficult to see, but are wingless simular to the adults. Both adults and the first two nymphal stages have rasping and sucking mouthparts.

Thrip species

Boree Gall (Kladothrips species) adults are gall producing thrips that form smooth bubble-like or irregular spiny growths on the leaves. These galls can contain up to 1000 insects that also reproduce inside, and are trapped until the gall dries or splits open. Commonly found in inland areas attacking the phyllodes of Acacia species.

Glasshouse Thrips (Heliothrips haemorrhoidalis) is a slender up to 15mm long with small fringed wings. The adult lays eggs on the underside of leaves where the nymphs emerge as miniature adults but wingless. Then feed on the soft leaves leaving a silvery mottled appearance.

Appearance and Distribution of the Pest

Thrips are found from tropical to temperate regions preferring a cool mild winter followed by a dry sunny spring that produces abundant flowers and new foliage. It is dispersed by flying and can be carries great distances on the wind.

Life Cycle

These insects have a Hemimetabolous life cycle, ie. When the immature nymphs resemble the adults.

The female adult lays her eggs using an oviposit in a slit on flower stems or occasionally leaves. The eggs develop into four nymphal stages. The first two stages occur on the plant and the last two in the surrounding soil or in leaf litter, emerging as adults and flying to reinfect the plant. It takes ten to thirty days to develop from egg to adult depending on the temperature and rainfall. Under opium conditions thrips are produced in plague proportions.

Period of Activity

Thrips are most active during warm dry, calm weather, but dislike the soil to be too dry or wet.

Damage Caused

Thrips congregate inside the flowers damaging the epidermal layer, allowing sap to leak out. This causes the flower petals to become brownish and curl along the margins. They also attack the upper surface of leaves causing a silvery discolouration as they suck the sap. The effect is a reduction in fruit and seed production on the host plant.

Susceptible Plants

Generally many plants species are attacked by thrips including buds, petals and leaves that are soft are at most risk, such as Alyogyne , Baeckea, Hibbertia, Hibiscus and Leptospermum species. There is also a wide range of ornamentals suseptable to attack including apples, pears, citrus, stonefruit, grapes and strawberries.

Buddleja species may be attacked by the thrip (Hercinothrips femoralis).

Cordyline, Agave, Dracaena and Howea species, Ficus elastica are attacked by the Dracaena Thrips (Parthenothrips dracaenae) which feed of the leaves.

Knightia excelsa is attacked by thrips by feeding on the chlorophyll in the leaf causing significant paling of the leaves. Stresses plants are more susceptible and plants rarely die from attack.

Peperomia, Cissus, Tropaeolum and Passiflora species and some fern species are attacked by Glasshouse Thrips which can cause heavy damage in inclosed areas such as a glasshouse.

Watsonia species are attacked by the Gladiolus Thrips (Taeniothrips simplex).

Cultural Control

There is no satisfactory cultural control. Small infestations may be ignored or the plant may be hosed to reduce the numbers. Removal of surrounding leaf litter, weeds and cultivating the soil can also reduce the numbers and disturb the life cycle. Care should be taken not to remove flowering weeds under trees that are in bloom as the thrips may migrate on to the tree, alternatively flowering annuals can be planted under trees to attract the thrips away.

Biological Control

No effective natural control though birds; wasp and other predators eat thrips. Weather conditions such as heavy rain help reduces numbers.

Chemical Control

Thrips can be sprayed with Dimethoate or Maldison at least twice every ten days to kill newly hatched nymphs, but may have a detrimental effect on other insects such as bees.

Note

Always read the label for registration details and direction of use prior to application of any chemicals.

DISEASE

   NAME

     Bacterial Soft Rot

     Erwinia species

Symptoms

Bacterial Soft Rot (Erwinia carotivora) infects the cell walls of the plant tissue causing the fluids to leak out making the areas soft and slimy. It commonly occurs at the base of the plant above or below ground level forming a soft dark patch and eventually the plant topples.  It is not instantaneous and crops are infected during harvested they can rot in storage as the infection takes hold.

Soft Crown Rot (Pectobacterium carotovorum) is a bacterial disease that normally occurs during hot humid weather and is found in the soil and infects the roots and crown of the host normally through wounds. The symptoms are a rot that causes the plant to wilt and die and generates a strong offensive odour.

Source and Dispersal

It dwells in soil or in host plant and is dispersed on insects or animals from infected plants and can also be dispersed by water.

Favoured Conditions

It prefers warm moist conditions.

Affected Plants

It prefers succulent stems, buds, roots or fruit of a wide range of plants including vegetables, perennials and tuberous plants.

Caladium species are venerable to several bacterial diseases that infect tubers, including (Pectobacterium carotovorum) and (Pellicularia rolfsii) both causes soft rot.

Cactus species particularly larger ones are infected by the Bacterial Blight (Erwinia carnegieana). This destructive disease produces small circular light coloured spots that are water soaked along the margins with the underlying tissues turning black.  It then turns blackish splits open and oozes brownish fluid.  Infected branches collapse and the disease spreads quickly through the plant.

Dahlia species may be infected by Tuber Rot (Pectobacterium carotovorum) that attacks stored tubers causing them to form brown soft rot.

Delphinium species are infected with the Bacterial Soft Rot (Erwinia phytophthora) that causes the top of the plant to dry out, giving off a foul smell. The upper stems become soft and blackish, causing the plant to be stunted and eventually die to ground level.

Delphinium species are infected by the Soft Crown Rot (Pectobacterium carotovorum) causing the death of the plant it also attacks Sansevieria species causing them to rot at the base.

Orchids such as Cattleya, Cymbidium, Cypripedium, Dendrobium, Epidendrum, Oncidium, Paphiopedilum, Phalaenopsis and Zygopetalum species are infected by Soft Rot (Erwinia species).

Saintpaulia and Philodendron species are infected by Bacterial Blight (Erwinia species) which forms brownish to black rot water soaked spots that can appear all over the plant.

Non-chemical Control

As a preventive measure cultivate the surrounding soil to improve drainage, aeration and minimise weed growth. Do not over water and allow the soil surface to dry before rewatering. When handling the plants pick a dry period and take care to minimise damage. Collected produce should be stored in a cool dry environment as the bacteria is inactive in temperatures below 4ºC.

At first sigh of infection the plant should be removed and disposed off.

Chemical Control

There is no satisfactory chemical control. It is important to take preventive measures.

Note

Always read the label for registration details and direction of use prior to application of any chemicals.

DISEASE

   NAME

     Fusarium Wilt (General)

     Various Wilt Species

Description

Fusarium wilt is caused by specialised strains of the common soil fungus, Fusarium oxysporum.This fungus is microscopic, and that can live in the soil for many years and primarily attacks plants by entering through the roots. This affects corms, stems and leaves by moving through the water conductive tissue in the plant.

The specialised strains are known as formae speciales (f. sp. or special forms) and each f. sp. has a relatively narrow host range. For example Fusarium oxysporum f. sp. cubense causes Panama wilt of banana, F. oxysporum f.sp. vasinfectum infects cotton and F. oxysporum f. sp. lycopersici attacks tomatoes. Each strain is specific to that narrow host range and will not affect other hosts; this is important as it makes control options involving the planting of other plant species possible.  

Symptoms

Generally the plant wilts quickly during hot weather or lacks growth and vigour. Typically the symptoms are often indistinguishable from drought stress. Leaves yellow and wither or stems split open near the base. Individual branches may collapse and die or entire plants perish. One of the distinctive symptoms is a one-sided yellowing and death of a leaf or branch. Corms become rotted with open wounds and affected stems, when split open are yellowish. There are variations in the symptoms depending on the type of plant but generally plants wilt, turn brown and die.

Basal Rot (Fusarium oxysporum) infects Tulipa and Crocus species by turning leaves reddish, which wilt and normally die. It also affects the bulbs by forming few roots and rotting the base, turning them dull white.

This disease also infects cactus such as Cereus species and Zygocactus truncatus causing soft black rot that appears at the tips of the plant then spread rapidly downwards.  It is particularly virulent in hot beds, under glass. The infected plants cannot be cured and should be disposed off site.

Fusarium Patch, Bent<      Fusarium Patch, Blue Grass

Other Fusarium (or related species) diseases

Fusarium Patch (Microdochium nivale formerly known as Fusarium nivale) is also known as Crown or Root Rot and infects warm or cool season Turf Grasses. The fungus infects the roots or rhizome turning them black, sometimes with a pink ting. During hot periods light green to brown patches appear in the turf as the damaged roots are unable to supply water to the leaves. This diseases is not a significant disease in Australia

Minimise irrigation of infected areas to reduce spread of infection as the spores are distributed in water.

Root Rot (Fusarium verticillioides) is a seed born fungus that infects Strelitzia reginae. It also forms a Leaf Spot in Dracaena species where rounded or irregular yellowish to reddish spots with a pail green border form. These are found on immature leaves and heavy infections may rot the crown.

Source and Dispersal

The fungal spores are dispersed by wind from infected plants or parts of plants. It is also dispersed by splashing water or contaminated stock or the movement of soil. With Fusarium wilt of canary island date palms the transfer of infected plant material on chain saws has been shown to be an important way in which the fungus can be transmitted from one tree to another. It is essential in these cases to sterilise the chain and chain bar between trimming the fronds on each tree.

Fusarium oxysporum produces three types of species, macroconidia, microconidia and chlamydospores. The latter two spore types play very important roles in the disease. The microconidia move in the vascular system of the plant and collect at the sieve plates in the xylem of plant. Here they germinate and grow and eventually block the sieve plate thus stopping the flow of water in the plant. The chlamydospores are specialised survival spores that persist in roots and in the soil for very long periods of time, thus allowing the fungus to survive periods when there are no susceptible plants present.

Favoured Conditions

The fungus prefers warm humid climates and is commonly seen in coastal regions and may continue living in soil for many years.

Affected Plants

Many species are infected including tomatoes, carnation, cucurbits and freesia. Die Back (Fusarium solani var. martii) causes damage to the branches of Ilex species. Fusarium also attacks palm species such as Phoenix causing wilt.

Albizia and Alternantera species are infected by the wilt (Fusarium oxysporum var. periciosum ) that causes the leaves to wilt, shrivel and die. This infection also extends to the branches and eventually may kill the tree.

Callistephus species are attacked by the wilt (Fusarium oxysporum f. sp. callistephi) which infects the vascular bundles turning brown, particularly on one side of the stem causing the plant to become stunted, eventually dieing.

Dendranthema and Thymus species are susceptible to the Stem Rot (Fusarium species) and (Pellicularia filamentosa) which rots the base of the stem.

Dianthus species are infected by Bud Drop (Fusarium poae). This fungus rots flower buds prior to opening and infected flowers open with distorted, unattractive petals. The control of thrips is essential. Dianthus species are also infected by Wilt (Fusarium oxysporum) that causes yellowing and wilting of the lower leaves, normally on one side. The infection causes stems to rot with vascular discolouration.

                  Fusarium Wilt Image by B. Sonsie

                  Image by Dr Brett Summerell

The only palms susceptible to Fusarium wilt are Phoenix species, especially Phoenix canariensis and juvenile Washingtonia filifera. Initially the leaflets turn yellowish then brown, on mature fronds causing them to die. Eventually only tufts of new growth remain the plant. As the infection continues the plant collapses and dies.

Fusarium Patch

Turf grasses are infected by Fusarium Patch (Microdochium nivale). Plants include; Digitaria didactyla (Blue Couch), Cynodon species (Couch), Eremochioa ophiuroides (Centipede Grass), Festuca species, Paspalum vaginatum (Salt Water Couch), Pennisetum clandestinum (Kikuyu), Poa species (Bluegrass), Stenotaphrum secundatum (Buffalo) and Zoysia species. Generally the fungus produces small dead circular patches in the lawn.

Non-chemical Control

Fusarium diseases are extremely difficult diseases to control primarily because of a lack of a chemical control option and because the fungus is able to persist in soil for long periods of time. Crop rotation to non susceptible plants is advised and consequently it will be important to have the disease accurately diagnosed to ensure the identity of the pathogen and the possible rotation options.

Remove and destroy any infected plants. In the case of large trees or palms, it will be necessary to remove the infected plant, this not only means cutting down the above ground parts, but also removing the roots of the plant. These will then need to be removed and destroyed.

Fusarium Patch can be minimised by reducing thatch and aerating the soil regularly or improving the drainage.

Chemical Control

There are no effective chemical control options currently available for plant diseases caused by Fusarium species.

Note

Always read the label for registration details and direction of use prior to application of any chemicals.

Amendments by

Dr Brett Summerell
Director Science and Public Programs
Royal Botanic Gardens Trust, Sydney