Effective control of kava wilt is a prerequisite to boosting domestic supply and developing export markets for the yaqona plant (Piper methysticum). Yaqona is the basis of the traditional drink kava used in rituals and ceremonies. The plant is important in the South Pacific, particularly in Fiji, Tonga, and Samoa, as a cash crop, an item of barter and a measure of wealth. It is also exported from some countries as a source of drugs for the pharmaceutical industry, particularly in the USA.

Kava wilt causes substantial annual production losses, with crop losses of 50% being reported from Fiji. The disease was first described in Fiji in 1935, but the causative agent has never been determined. Disease symptoms include dark brown to black lesions on the leaves and stems, with affected stems developing a black rot. The vascular system turns black and the roots also rot. Similar symptoms have been reported from Tonga, Samoa and Vanuatu.

The objectives of this project are: 1) to identify the cause of kava wilt; 2) to determine the life cycle of the pathogen and the means by which the disease is spread; 3) to determine possible control strategies such as use of resistant cultivars, changed cultural practices, chemical and physical treatments, and biological control.

Surveys of yaqona crops in various Pacific Islands where the disease is thought to occur will ascertain the distribution and relative importance of the disease in the South Pacific. Field trials will investigate the effectiveness and economic feasibility of different strategies used to control kava wilt. Some examples are: trials to confirm whether cultivars containing purple pigment are more resistant than green-stemmed types; trials with disease-free planting material, obtained from disease-free stands or by physical or chemical treatments; tests of cultural practices such as rotation with other crops, improved nutritional status of soils, weed control and drainage; trials with foliar sprays, dips or soil drenches to reduce incidence fo the disease; investigation of biological control methods.

Epidemiological studies will determine how the causal organism survives and spreads. Knowledge of the factors affecting survival and spread of the pathogen and conditions for increase of the disease within yaqona plantings will enable formulation of sound control strategies. A pathologist will be stationed in the South Pacific, initially in Tonga, to conduct the experimental program in collaboration with Pacific island pathologists.

Control of kava wilt would have an immediate beneficial effect on yaqona production. In addition, agronomists would be able to select superior cultivars and ascertain the effects of different cultural practices on yield and quality. This is not presently possible because of the masking effect of the disease.