It's distress time for farmers in Chamarajanagar district. Papaya mealybug (common name) or paracoccus marginatus williams/granara de willink (scientific name) has emerged as a serious threat to a number of horticulture crops, ornamental plants and mulberry cultivation. The infestation has damaged papaya crop worth more than Rs.1.50 crore.
The district has a geographical area of 5.69 lakh hectares, of which 2.04 lakh hectares is fit for agriculture. Horticulture crops are being cultivated on 36,985 hectares and mulberry plants on 4,701 hectares. Of the papaya crop area of 476 hectares, papaya on 148 hectares and mulberry plants on 100 hectares were badly affected. The pest has caused damaged mulberry crop worth Rs.1 crore.
The list of affected crops also include jatropha, cassava, shoe flower, guava, cotton, brinjal, redgram, tomato, eggplant, pepper, mango, cherry, pomegranate, citrus, hibiscus, beans and peas. Many weed hosts such as congress grass (parthenium hysterophorus), country mallow (Abutilon indicum), Hazardani (phyllanthus niruri), chandvel (convolvulus arvensis), garden sprug (Euphorbia hirta), wild mustard (cleome viscosa), and spider wort (commelina benghalensis) support development and spread of papaya marginatus. Removal and destruction of such hosts are important and essential part of pest management.
The papaya mealybug was discovered in Manatee and Palm Beach, Florida, in 1998 on hibiscus. It subsequently spread to several other areas. The serious threat of papaya mealybug on tropical fruits and ornamental plants has been noticed since 2008 in Tamil Nadu.
The movement of papaya marginatus fruits, stems of tapioca and mulberry infested with pest to the border district of Chamarajanagar subsequently spread to Nagavalli, Malledevanahalli, H.D. forest, Timmegowdanapalya, Gangavadi and Muntipalya in Chamarajanagar taluk, Kannegala, Annurkeri, Lakkur, Hundipura, Chowdalli and Vaddagere in Gundlupet taluk, Hanur, Uddanur, Hullepura and Kinakanahalli in Kollegal taluk and Dasanahundi, K.Devarahalli and Honnur in Yelandur taluk.
Drying of leaves
Papaya mealybug infestations are typically observed as clusters of cotton-like masses on the above-ground portion of plants. The mealybugs are white to pink in colour and measure 3-4 mm in length. Adult females are oval and round, dark green to almost black in appearance. Mealybugs feed on the sap of plants by inserting their stylets into the epidermis of the leaf as well as into the fruit and stem, causing yellowing and drying of leaves, bunchy top of terminal shoots, and dropping of flowers and fruits. Heavy infestations are capable of rendering the fruit inedible due to build up of thick white wax. The bugs are most active in warm, dry weather.
Under greenhouse conditions, bugs reproduce throughout the year, and in certain species it may occur without fertilization. The bugs lay eggs in a sac of white wax, usually clusters, on the twigs, branches or bark of the host plant. Non-infected plants can be infected from infected plants as juvenile mealybugs crawl.
Small crawlers are transported by wind, rain, birds, ants etc., and they settle in new plants. Heavy clustering of mealybug can be seen under the leaf surface, giving the appearance of a thick mat with waxy secretion.
They excrete copious amount of honey dew that attracts ants and helps in development of black sooty mould which inhibits the plant's ability to manufacture food.
Biological control was identified as a key component in a management strategy for the papaya mealybug. A number of natural enemies of the papaya mealybug include the commercially available mealybug destroyer Ladybird beetles (Cryptolaemus montrouzieri), Lepidopteran larva (spalgis epuis), lacewings and hover flies.
These predators have a potential impact on mealybug populations. If noticed in any of the infested areas, they should be collected and released into other infested areas/plants with follow up for their efficacy, as was done in the case of cotton mealybug in various States.
Infestations on ornamental plants such as shoe flower and Nerium in home gardens can be reduced through the spray of botanical insecticides such as neem oil and neem seed kernel extract.
A number of chemical controls are available to control mealybugs, although none are currently registered specifically for control of papaya mealybug.
Typically, twice the normal dose is applied when treating for mealybug because mealybugs are protected by thick waxy and buds. Thus, chemical controls are only partially effective and require multiple applications.
Furthermore, problems with insecticide resistance and non-target effects make chemical control a less desirable control option. Crop residues in previously infested fields should be removed and burnt. Field borders should be free from weeds and debris. Creating awareness on identity, severity, host range and mode of spread of pest among farmers must be the first step.
Necessary hand-outs on this pest may be prepared in vernacular languages and distributed in villages. Farmers may be trained for early detection of mealybug in their crops and non-crop hosts and this should be reported to local government and non-government institutions which could be drafted for weekly field visits and surveys.
Good agricultural practices such as field sanitation, regular weeding, frequent monitoring through field visits, removal and destruction of plant parts and use of clean farm implements should be the basic strategies for tackling the spread of mealybug before applying insecticides.
According to experts, climate change had a significant influence on the outbreak of the pest. Climate change enhanced the temperature and carbon dioxide in the atmosphere which altered the physiology of the crop, predisposing them to the pest attack. Comprehensive surveillance and monitoring programme for early detection and effective management of the pest is the need of the hour.