Here is a list of pests that damage ornamental plants.
1. Groundnut Aphid, Aphis Craccivora Koch (Hemiptera: Aphididae):
This black coloured aphid species attacks Bougainvillea spp. from December to February. Both adults and nymphs infest flowers, tender leaves and the terminal portions of the plant and suck cell sap. Its attack results in the premature fall of the flowers and the downward cupping of the leaves.
2. Cotton Aphid, Aphis Gossypii Glover (Hemiptera: Aphididae):
Both adults and nymphs suck plant sap of many ornamental plants like Hibiscus rosa-sinensis Linn., Cassia glauca Linn., Tecoma capensis Lindl. and Rosa spp. from September to April in northern India. The maximum population is observed in H. rosa-sinensis during March-April. On Rosa spp., it is also observed in September-October and on C. glauca in March-April.
As a result of its attack, a sooty mould develops which results in a blackened look of the plants. The adults are small, soft and greenish-brown insects. They are parthenogenetic and viviparous giving birth to 8-20 nymphs per female per day. The nymphs moult 4 times to become adults in 7-10 days.
The other common aphid species which also attack ornamental plants are Aphis nerii Boyer de Fonscolombe on Asclepias curassavica Linn, and Aphis fabae solanella Theobald on Castrum nocturnum Linn. The maximum infestation of both the aphid species is found from February to April. As a result of excessive feeding by adults and nymphs on the plant sap, the leaves curl downwards and the plants give a very shabby look.
3. Dusky Cotton Bug, Oxycarenus Laetus Kirby (Hemiptera: Lygaeidae):
The nymphs and adults of this pest species are commonly found feeding on Hibiscus rosa- sinensis Linn., Dambeya natalensis Send., D. spectabilis Cav., Malvaviscus arboreus Fabr., Bougainvillea spp., Jasminum grandiflorum Linn., J. multiflorum Andr., J. humile Linn., Bauhinia acuminata Linn, and Plumeria acuminata (Linn.) throughout the year except during winter months.
The host plant, H. rosa-sinensis is most preferred by this bug. The maximum population of the insect is found from March to May. The flower buds of Hibiscus plants become pale as a result of its feeding and fall down without opening. The adults usually feed on the terminal portions. They hide in the clusters of dry leaves and flowers during December-January.
4. Ak Grasshopper, Poekilocerus Pictus (Fabricius) (Orthoptera: Pyrgomorphidae):
Ak grasshopper is one of the common grasshopper species occurring in India, Pakistan and Afghanistan, it is primainly a pest of Calotropis spp., viz. C. gigantea and C. procera. It is also highly destructive to over 200 species of host plants including field crops, vegetables, fruit trees and ornamental plants.
5. Red Cotton Bug, Dysdercus Koenigii (Fabricius) (Hemiptera: Pyrrhocoridae):
It is a bright red bug 15 mm long, having black spots on the wings. Both adults and nymphs feed on Hibiscus rosa-sinensis Linn., Dombeya spectabilis Cav., D. natalensis Sind., Carissa carandas Linn., Buddleia madagascariensis Lamk. and Jasminum sambac Linn., from April to December. Out of all its host plants, H. rosa-sinensis is the most preferred one. As a result of severe sucking of sap from the leaves and flower-buds, vitality of the plants and their flowering capacity is reduced.
6. Citrus Psylla, Diaphorina Citri Kuwayana (Hemiptera: Aphalaridae):
The citrus psylla is a serious pest of Murraya paniculata Jack, from April to July. It also feeds on Plumeria acuminata Linn., Dombeya spectabilis Can. and Duranta plumieri Jacq. The nymphs and adults suck sap of the fresh leaves and tender parts of the plants, and thus vitality of infested plants is reduced, giving them a sickly appearance.
7. Cotton Whitefly, Bemisia Tabaci (Gennadius) (Hemiptera: Aleyrodidae):
The cotton whitefly is found feeding on Euphorbia pulcherima Wild., Hibiscus rosa-sinensis Linn., Lantana camara Linn., Dombeya spectabilis Cav. and Poinciana pulcherima (Linn.) from May to October. The maximum population is found in August-September on all these host plants. The attack of the whitefly results in downward cupping of the leaves. A sooty mould develops on the leaves which give blackish look to the plants. With excessive sap sucking, the leaves fall down.
8. Grapevine Thrips, Rhipiphorothrips Cruentatus Hood (Thysanoptera: Thripidae):
The grapevine thrips attacks many ornamental plants like Rosa spp., Lagerstroemia indica Linn, and Punica granatum Linn, from August to January. The infestation becomes heavy on P. granatum and Rosa spp. during September-October. As a result of severe feeding, the leaves turn rusty brown, particularly from the undersurface and ultimately they fall down.
9. Jasmine Thrips, Thrips Orientalis Bagnall (Thysanoptera: Thripidae):
The dark coloured jasmine thrips is mainly found on Jasminum multiflorum Andrs. from February to April. Both adults and nymphs feed on flowers. The attacked flowers give a decayed look and fall off prematurely.
Another thrips species, Taeniothrips traegardhi Tryban, also attacks the flowers of Nerium indicum Mill, and Daedolacanthus nervosus T. Sandwss. in the months of March-April. The insects are light brown in colour and are found in flowers, giving them a decayed look caused by feeding.
10. Bihar Hairy Caterpillar, Spilarctia Obliqua (Walker) (Lepidoptera: Arctiidae):
The caterpillars of this polyphagous insect attack the ornamental plant, Barleria cristata Linn, during October-November and December-January. They feed on leaves and floral parts of the plant.
In many cases, the whole leaf is eaten away by the caterpillars.
11. Castor Hairy Caterpillar, Euproctis Lunata Walker (Lepidoptera: Lymantriidae):
The castor hairy caterpillar, in addition to castor, is also found on Lagerstroemia indica Linn., Punica granatum Linn., Hibiscus rosa-sinensis Linn, and Rosa spp. during September-October. The young larvae eat the leaf margins of the host plants. The full-grown caterpillars, however, feed on the entire leaf lamina and cause maximum damage during these months.
12. Jasmine Gallery Worm, Elasmopalpus Jasminophagus Hampson (Lepidoptera: Pyralidae):
The greenish larva has a red head and prothorax with brown streaks on its body. The moth is narrow, long and dark grey with pale hind wings, grows to a length of 2.5 cm. The larva in the early instars feeds inside buds. It webs together the terminal leaves, shoots and flower head and feeds on them. Faecal matter can be seen attached to the silken web. Pupation takes place inside the web itself. All varieties of jasmine are attacked.
13. Pea Leafminer, Chromatomyia Horticola (Goureau) (Diptera: Agromyzidae):
The pea-leaf-miner is a polyphagous pest. It feeds on a large number of cruciferous plants, antirrhinum, nasturtium, pea, linseed and potato. The larvae of this pest are very destructive and make prominent whitish tunnels in the leaves.
14. Cotton Grey Weevil, Myllocerus Undecimpustulatus Faust (Coleoptra: Curculionidae):
The cotton grey weevil is commonly found from July to September on Hibiscus rosa-sinensis Linn., Lagerstroemia indica Linn., L. speciosa Ders., Bauhinia acuminata Linn., Dombeya spectabilis Cur., D. natalensis Sond., Thuja occidentalis Linn, and Malvaviscus arboreus Fabr. The adults feed on the leaves of these host plants in an irregular fashion, starting from the leaf margins.
In addition, the other weevil species belonging to family Curculionidae, namely Tanymecus sp. also feeds on Rosa spp. during July-September; Alcidodes sp. feeds on Lagerstroemia indica in April- May and Amblyrrhinus sp. feeds on various ornamental shrubs like Lagerstroemia indica L., L. speciosa Pers., Lawsonia inermis Linn., Rosa spp., Bauhinia acuminata Linn, and Poinciana pulcherrima Linn, from March to October. The adults of all these weevils feed on the leaves and flowers of the host plants.
15. Cotton Mealybug, Phenacoccus Solenopsis Tinsley (Hemiptera: Pseudococcidae):
Cotton mealybug has recently emerged as a serious pest of a number of agricultural crops including cotton, tomato, mustard, sorghum and ornamental plants.
16. White Grub, Holotrichia Consanguinea Blanchard (Coleoptera: Scarabaeidae):
The adults of the white grub feed on Acalypha tricolor Seem., Bauhinia acuminata Linn., Jatropha intergrima Linn., Lagerstroemia indica Linn., L. speciosa Pers., Punica granatum Linn., Rosa spp. and Thuja occidentalis Linn, during the period June to August and they completely defoliate the host-plants.
Another dark-brown chaffer beetle, Schizonycha sp. also commonly feeds voraciously on the leaves and flowers of Lagerstroemia indica L., L. speciosa Pers., Rosa spp. and Punica granatum Linn, from May to July. This beetle is nocturnal in habit and starts its activity soon after sunset.