Photo 1. Kava leaf showing yellow-green mosaic patterns and distortions typical of infection from Cucumber mosaic virus.
Cucumber mosaic virus causes kava dieback; the abbreviation is CMV.
Worldwide. In temperate, sub-tropical and tropical countries. Cucumber mosaic virus has been recorded in kava causing dieback from Cook Islands, French Polynesia, Fiji, Palau, Samoa, Tonga, and Vanuatu.
A virus with a large host range. It is especially common in the families Curbitaceae, Fabaceae and Solanaceae. In Pacific islands, the following crops are common hosts: kava, banana, cantaloupe melon, capsicum, chilli, pumpkin, snake gourd, tomato and watermelon. Cucumber mosaic virus has also been found in weeds, e.g., Ruellia, Synedrella, Mikania and Commelina.
The first sign of the disease is young leaves with sharply defined patches of yellow or white (Photo 1). This is called a mosaic symptom, and it usually occurs together with leaf distortions, such as a crinkling or puckering along the veins (Photos 1&2). If the stems of these leaves are cut, brown lines are seen inside. This is the start of the black soft rot of the stems (Photo 3).
Cycles of dieback and regrowth often occur before the plant dies. Very occasionally, the leaves on diseased plants also wilt.
Aphids spread the virus. This can happen very quickly. As the aphids feed on diseased plants they pick up the virus with their mouthparts. If they fly to healthy plants and feed again, those plants become infected. The melon or cotton aphid (Aphis gossypii) is common on kava as well as on many other crops and weeds. The virus is also spread when cuttings from infected plants are used for propagation.
This is a very serious disease. Losses are high in all the major kava-growing countries.
Look for leaves that have mosaic patterns and distortions. Look for early signs of stem rot at tips or at lower nodes (the swollen part of the stem from where the leaves grow).
Cultural control is the only way to manage kava dieback:
There is no known resistance among the varieties of kava grown in Fiji, Samoa and Tonga.
Chemical control is not appropriate for this disease. There are no chemicals that can rid plants of virus, and although many insecticides kill aphids, they cannot kill them before they feed and spread the virus.
AUTHOR Grahame Jackson & Richard Davis
Information (and Photos 1-3) from Davis RI (2005) Kava dieback. Plant Advisory Leaflet No. 47. Secretariat of the Pacific Community. Quality Print, Suva, Fiji Islands. 4pp.; and from Mereia Fong-Lomavatu et al. (2006) Yaqona dieback disease management: A package of practice. Koronivia Research Station, Ministry of Primary Industries, Fiji Islands. 4pp.
Produced with support from the Australian Centre for International Agricultural Research under project PC/2010/090: Strengthening integrated crop management research in the Pacific Islands in support of sustainable intensification of high-value crop production, implemented by the University of Queensland and the Secretariat of the Pacific Community.
This fact sheet is a part of the app Pacific Pests and Pathogens
The mobile application is available from the Google Play Store and Apple iTunes.