PLANT PROTECTION 1 â Pests, Diseases and Weeds

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PLANT PROTECTION 1 – Pests, Diseases and Weeds Longtailed mealybug Scientific name Pseudococcus longispinus (Pseudococcidae, Order Hemiptera). This is a common and key pest in NSW, Victoria and WA. It is a minor pest in the NT. Other mealybugs include: Citrus mealybug (Planococcus citri) Citrophilous mealybug (Pseudococcus calceolariae) Root mealybug (Rhizoecus spp.) Hibiscus mealybug (Maconellicoccus hirsutus) Grass-crown mealybug (Antonina graminis) Tuber mealybug (Pseudococcus affinis), the most important root-feeding mealybug in Australia See also page 144. Closely related to scales but mealybugs remain mobile throughout their lives. Mealybugs are a major cause of plant damage in greenhouses. Host range Very wide host range. A serious pest of both indoor and outdoor plants in warm, humid climates, rarely attacks annuals but is an important pest of perennial plants. They attack roots, stems and leaves. Woody trees, shrubs and ferns are the most important plants infested. Ornamentals, eg trees and shrubs, herbaceous plants, ferns, orchids, bulbs, African violets, cacti, indoor plants, ornamental grasses, eg Papyrus, a major greenhouse pest. Fruit, eg citrus, custard apple, grapes. Pastures, field crops, clovers. Description & damage Adult females are 3-5 mm long, slow moving, oval, wingless, flattened with well developed legs. Their bodies are covered with wax glands which secrete a white mealy wax (hence the name mealybug), which forms short hair-like filaments at the sides of the body. The hind end bears a pair of wax filaments which are usually longer than the body and may be broken off. They have well developed legs and antennae and when disturbed or seeking fresh feeding sites, crawl slowly but freely. The length of the side filaments are about ½ the length of the body. Adult males are tiny, delicate winged insects with long waxy tail filaments, but are rarely seen. Nymphs. 1 st stage nymphs (crawlers) are minute, pink and mobile. Later stage nymphs resemble adult females. Males resemble females, but later form cottony cocoons about 3 mm long within which they develop. A colony can be almost completely enveloped in a woolly mass. Above-ground damage. Mealybugs feed on stems and leaves by sucking sap and congregate in sheltered parts, eg sheaths, leaf bases, leaf undersurfaces, around buds, stems, lower parts of fronds, crowns, flowers, where 2 pieces of fruit touch. Infestations are often not noticed until numerous and unsightly. Sap feeding distorts and yellows foliage. Unchecked infestations on soft-leaved plants, eg African violet, cause them to wilt and die. Economic damage on many plants is caused by the large quantities of honeydew produced; sooty mould develops on it, disfiguring leaves, stems and fruit. Large infestations make plants unsaleable. Ants are attracted to honeydew. Coastal brown ants (Pheidole megacephala) tend mealybugs for honeydew and move them around and fend off natural enemies. Overseas mealybugs have been recorded as transmitting virus diseases, eg citrus mealybugs possibly vector banana streak virus (BSV). Below-ground damage. Other species may also feed on roots and this may not be noticed until the plant is repotted, wilts or dies. Diagnostics. Check roots of wilted plants for mealybugs. Indoor plants often have large numbers of some species before their presence is noticed. Do not confuse: – Mealybug colonies with fungal growth. – Mealybugs with the larvae of mealybug ladybirds which feed on mealybugs. Ladybird larvae are about 3 times as long as mealybugs. They have long marginal filaments, are also covered with white mealy material, but they are more active and have biting mouthparts (Fig. 109 below). Identification of species depends on: – Length of anal filaments. – Colour of body fluid exuded from dorsal glands. – Presence of wax-free areas along the back. – Expert help is usually needed. Longtailed mealybug has tail filaments longer than its body. When squashed, body fluid is pale yellow and there is no wax-free area along the back. Eggs laid beneath the body hatch almost immediately. Do not confuse with: – Citrophilous mealybug with tail filaments about rd its body length, 4 dark longitudinal dorsal stripes. Body fluid dark red, eggs laid in cottony sac. – Citrus mealybug with tail filaments not more than rd body length, median dorsal stripe. Body fluid yellow-orange, eggs laid in cottony mass. Longtailed mealybugs, 3-5 mm long. Cluster of mealybugs. Mealybug ladybird larvae 8-15 mm long. Fig. 109. Longtailed mealybug (Pseudococcus longispinus). Photos NSW Dept of Industry and Investment. 160 Insects and allied pests - Hemiptera (bugs, aphids, etc) Cluster of mealybug ladybird larvae.
PLANT PROTECTION 1 – Pests, Diseases and Weeds Pest cycle There is a gradual metamorphosis (eggs, nymphs (3-4 stages) and adults) with several overlapping generations per year in NSW and Vic and SA. Longtailed mealybugs produce about 200 young in 2-3 weeks. Eggs hatch as they are being laid. Eggs of other species, eg citrophilous and tuber mealybugs, are laid in a loose cottony mass, light yellow crawlers hatch 3-9 days later. Life cycle takes about 6 weeks in summer and about 12 weeks in winter. ‘Overwintering’ Outdoors, as eggs during cold weather. In greenhouses and warm climates the cycle is continuous. On citrus most longtailed mealybugs 'overwinter' as juveniles which reach adulthood by Aug-Sept. Mealybugs can ‘overwinter’ on weeds growing in paths, etc which can lead to rapid reinfestation. Spread Mealybugs move around only short distances very slowly to find better feeding sites. Movement of infested plants into glasshouses, purchasing infested plants, taken to displays, etc. By wind and visiting insects. By ants, birds and on worker’s clothing. Ants tunnel through soil and potting mix to move young root mealybugs from plant to plant (including weeds) quickly spreading these pests throughout a nursery. Conditions favoring Warm, humid conditions, as in greenhouses, bathrooms. Sprays used to control other pests kill off ladybird and lacewing predators which usually suppress mealybug populations. Weakened plants, eg those grown in very dry situations or those held in pots for too long. Thickly-foliaged mature trees. Shade. Dusty trees. Ants attracted to honeydew discourage the predatory mealybug ladybirds (Cryptolaemus). Plants with a high nitrogen content. Management (IPM) Are you a commercial grower or home gardener? 1. Obtain/prepare a plan that fits your situation. 2. Crop, region. Obtain a program for longtailed mealybugs on your crop in your region. 3. Identification can be difficult. Consult a diagnostic service to avoid confusion with other species of mealybugs (page xiv). Fig. 110. Pest cycle of the longtailed mealybug (Pseudococcus longispinus). Insects and allied pests - Hemiptera (bugs, aphids, etc) 161
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Insect secretions PLANT PROTECTION
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Control methods Cultural methods.
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Root structure of dock (Rumex spp.)
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PLANT PROTECTION 1 â Pests, Diseases and Weeds