The epidemiology of the rust fungus Endophyllum osteospermi was investigated. This rust fungus is considered to be a candidate biological control agent for Chrysanthemoides monilifera ssp. monilifera, which is an invasive alien weed of native vegetation in south-eastern Australia. Between 10 and 20 plants of C. monilifera were marked at each of five sites in the Western Cape Province of South Africa, where both organisms are native. The infection levels and number of witches¿ brooms were determined every 2 months over a 2-year period. Additionally, at three of these sites, the infection levels and number of witches¿ brooms of all bushes in the host population was determined annually over 4 years. The increase in number of witches¿ brooms per bush ranged between 0 and 282 within 1 year, with an average increase per bush of 28 (SE±4.8) in 1993, and 39 (SE±9.2) in 1994. The average rs for all bushes during 1993 was 0.015 month¿1 (SE±0.0041, n=72) and 0.0098 month¿1 (SE±0.0073, n=43) during 1994. When host bushes that either died back or died during the course of each year were excluded, then the average rs during 1993 was 0.023 month¿1 (SE±0.0048, n=45) and 0.0348 month¿1 (SE±0.0106, n=20) during 1994. Under suitable conditions in South Africa, E. osteospermi undergoes epidemic increase within its host plant's populations. This rust fungus should therefore be considered as a suitable candidate biological control agent for use in Australia against C. monilifera ssp. monilifera.