The use of plant pathogens for biological weed control in South Africa.
The use of pathogens for the biological control of Acacia saligna, Hakea sericea, Ageratina adenophora and Ageratina riparia in South Africa over the last decade is reviewed. An Australian gall-forming rust fungus, Uromycladium tepperianum, has been introduced and, since 1987, inoculated onto A. saligna at over 50 localities throughout the distribution of the weed. Two exotic leaf pathogens, Phaeoramularia sp. and Entyloma ageratinae, were introduced during 1988 and 1989, resp., to control A. adenophora and A. riparia. All three pathogens are dispersing naturally, but it is still too early to evaluate their effect on the weed populations. A locally occurring strain of the fungus, Colletotrichum gloeosporioides [Glomerella cingulata], which causes a fatal disease of H. sericea has been exploited. A formulation of the pathogens for application to young seedlings of the weed is currently being developed commercially.