During a one year survey for microorganisms associated with hydrilla
(Hydrilla verticillata), approximately 2200 microbes were recovered from
hydrilla, surrounding water, and sediment coflected from 10 man-made ponds
and three natural lakes in Florida, USA. A representative selection of fungi
(651), bacteria (330), and actinomycetes (38) from this collection was
screened against hydrilla in bioassays. Severity of damage (DS) was
determined on a scale of 0 to 4, where 0 = healthy, 1 = 1-25% damage, 2 =
26-50% damage, 3 = 51-75% damage, and 4 = 76-100% damage (100% =
complete kill). Of the 1019 isolates that were examined in this manner, none
of the actinomycetes were pathogeniC on hydrilla. however 2 strains of
bacteria (0.6% of the bacteria tested), and 42 isolates of fungi (6.5% of thl
fungi tested) were effective at DS level 4 on hydrilla 3 weeks post inoculation
Fungi and bacteria capable of killing hydrilla are considered to have potentia
as biocontrol agents or as sources of novel herbicidal metabolites. These~
included Acremonium sp., Botrytis sp., Curvularia sp., Cylindrocarpon sp.,'
Fusarium culmorum, and F. moniliforme. The blocontrol potential of F.
culmorum has been established in several tests. For maximum bioherbicidal
activity of this fungus against hydrilla, its inoculum should be applied at a rate
of 5 x 10⁵ conidia/ml at 20 to 25°C water temperature.