Biology Reference
In-Depth Information
appears to be successful; however, possible contamination of agricultural lands
from runoff water from treatment areas is a concern that should be addressed when
using the R. solanacearum as a biocontrol agent (Anderson and Gardner 1999).
10.3.4
Eichhornia crassipes (Mart.) Solms-Laub.
(Water hyacinth)-Insects and Pathogens
The Neotropical invasive aquatic plant water hyacinth ( Eichhornia crassipes Mart.-
Solms-Laub., Pontederiaceae), also called the blue devil, continues to plague many
regions of Africa, Asia, Central and South America, and Pacific islands, including
many managed and natural forests where human activities are responsible for the
weed's establishment and proliferation. Mechanical removal, biological control
agents, and chemical herbicides, used alone or in integrated systems, have been
reasonably effective for management of water hyacinth on small scales and for
short durations at different sites and regions, but the weed remains a recurrent prob-
lem throughout the world. Biological control by using insect herbivores (most
notably two weevils: Neochetina bruchi Hustache and N. eichhorniae Warner),
naturally occurring pathogens ( Acremonium zonatum (Saw.) Gams, Alternaria
eichhorniae Nag Raj & Ponnapa, Cercospora piaropi Tharp emend. Conway
emend. Tessmann et al.,) and others, and generalist microbial colonizers used in
judicious combinations with chemical herbicides and mechanical methods appears
to offer a sustainable, long-term solution to the water hyacinth problem (Charudattan
2001). To be effective, the integrated management system should include all appro-
priate and effective methods of control with biological control serving as the center-
piece (Charudattan 1986). Improvements in the effectiveness of biological control
beyond what has been achieved thus far in different parts of the world appear likely
through deployment of additional insect and microbial agents (Julien 2001; Evans
and Reeder 2001). Although addition of agents to the integrated water hyacinth
management system may result in negative rather than additive or synergistic
effects, in the case of Eccritotarsus catarinensis (Carvalho) (Heteroptera: Miridae),
introduced in South Africa in 1996, the effects appear to be generally complemen-
tary to those of five previously established arthropods (Coetzee et al. 2005).
There are several reviews on pathogens of water hyacinth and their development
and use as bioherbicides (Bateman 2001; Charudattan 2001; Shabana et al. 1997).
Among the pathogens that have been studied extensively are Acremonium zonatum
(Jiménez and Balandra 2007), Alternaria eichhorniae (Shabana et al. 1995, 1997),
and Cercospora piaropi (Charudattan et al. 1985; Tessmann et al. 2001, 2008).
Although some recent surveys have been done to find new pathogens (Evans and
Reeder 2001; Jiménez and Charudattan 1998), no new candidate has emerged that
is better than the known pathogens. While the possibility of finding a previously
unknown pathogen with great potential cannot be dismissed, any new attempt at
developing a bioherbicide formulation has to rely on one of the three pathogens
mentioned here. In this regard, C. piaropi is still the leading candidate in our estimation
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