Waterhyacinth ( Eichhornia crassipes [Mart.] Solms), of South American origin, continues to
be one of the most prolific aquatic weeds in the world. Since its introduction into Mexico in the late 19th Century (5), it has become a focus of intense control efforts in that country, as well in others. From a study carried out to identify fungi associated with waterhyacinth in Mexico, two species with biological control potential were identified: Cercospora piaropi Tharp
and Acremonium zonatum (Saw) W. Games (4). Two Cercospora spp., C. rodmanii and C. piaropi,
as well as A. zonatum, are known to attack waterhyacinth. The host specificity of C. rodmanii (previously considered different tu C. piaropi in conidia morphology) was demonstrated in an evaluation of 58 species (1). Rintz (6) reported that an isolate of A. zonatum from Louisiana (USA) attacked 10 of 12 species tested. The aim of our study was to determine the host specificity of C. piaropi and A. zonatum (isolated in Mexico) in order to evaluate their
potential as biocontrol agents for waterhyacinth. The plant species included in the test were selected on the basis of their economic (8) and ecological (7) importance and their relation to the target plant, waterhyacinth (1,8).