Environmental Engineering Reference
In-Depth Information
biological control alone, although the overall effectiveness is sometimes compro-
mised by environmental factors such as fl oods and frost, and alternative manage-
ment practices, such as nutrient enrichment and herbicidal control (Fig. 10.2).
(a)
(b)
Fig. 10.2
A 7km-long infestation of water hyacinth (
Eichhornia crassipes
) on
the Vaal River, South Africa, a high altitude site that experiences cold winters
(a). Biological control agents, namely
Neochetina eichhorniae
,
N. bruchi
,
and
Niphograpta albiguttalis
,
were released onto this system in the early 1990s. It has
taken more than 15 years for these agents to have a signifi cant impact on this
infestation which is now signifi cantly reduced, and is characteristic of biocontrol
of tropical weeds in temperate regions (b).
