Diseases of Pyrethrum in Tasmania: Challenges and Prospects for Management.

Abstract

Pyrethrum (Tanacetum cinerariifolium (Trevir.) Sch. Bip.) is a perennial plant and member of the Asteraceae that is endemic to the Dalmatian region of the former Yugoslavia (36). Pyrethrum is cultivated commercially solely for the production of six closely related esters called pyrethrins. The plant is tufted, slender, and herbaceous, growing to a height of approximately one meter (18). Leaves are alternate and pinnately lobed/narrowly lanceolate to oblong lanceolate. The daisy-like flowers are produced at the termini of stems and consist of a cluster of 40 to 100 bisexual, yellow disk florets encircled by a ring of 18 to 22 pistillate white ray florets atop a moderately convex to subglobose receptacle (Fig. 1; 100). Disk and ray florets both possess 3 to 10 ribbed achenes located between the floret and receptacle. Involucres generally range between 12 and 18 mm in diameter (17,18). Approximately 94% of the pyrethrins are produced within secretory ducts and oil glands of the achenes of the mature pyrethrum flower, with a minor percentage of oil glands and secretory ducts also found in leaves, stems, and roots (99). Pyrethrins can be separated into two groups of three ester compounds: pyrethrins I and II. The pyrethrin I fraction contains chrysanthemic acid products, including pyrethrin I, cinerin I, and jasmolin I. The pyrethrin II fraction is derived from pyrethric acid and made up of pyrethrin II, cinerin II, and jasmolin II (19,27). Compounds within both fractions contain insecticidal properties used in household and commercial pest control products. These compounds are referred to as “knockdown” and kill agents for many arthropods, yet are of low toxicity to mammals. Pyrethrins also have the advantage over other synthetic insecticides of being rapidly broken down upon exposure to light and air, are metabolized quickly, and can be used in the production of organic farm products. Thus, natural pyrethrins are generally considered to be nonpolluting (19,27). The major areas of pyrethrum production worldwide are located in East Africa (Kenya, Rwanda, and Tanzania), Tasmania (Australia), China, and Papua New Guinea (85,94). Production of pyrethrum in Kenya began in 1928, and despite some fluctuations in annual supply, Kenya is still one of the major suppliers to the world’s market. Pyrethrum cultivation in Kenya is centered in four production areas: the northern and southern Rift Valleys, Mount Kenya, and near Lake Victoria (94). Tasmania is the other major world producer and grows approximately 2,000 hectares. In Tasmania, pyrethrum is grown predominantly along the northwest coast of the island, between Deloraine (41° 31′ S; 146° 39′ E) and Table Cape (40° 56′ S; 145° 43′ E). The cultivation of pyrethrum differs markedly between Tasmania and the other production areas of the world. For example, in 2001 approximately 200,000 growers were involved in pyrethrum production