tht-' gr;-1pncl i~-; then thro':Jn over ~he -:::.c•p l)f o. quu.ntil:y of
fluciting wo.tcr hyacinth. As tl1e tC>elh bite i:1to the weed
co.p:.u~-..ed portic~n of \\Veed away fr~1m the flt)Gt.i ng mass. The
amount of \\·Jeed torn cnvay .,.,ill be related, of course, to the
power of the boat's engine. This operation can be repe3ted,
ideally using several boats, to clear masses of \\1:eed away from
banks and the mouthsof blocked creeks.
The :nethod of using grapnels to control weeds is likely to be
labour-intensive but may be practical where the use of boats
can be donated and 13.rge numbers of volunteer workers are
3'¥'1ilable. The main problem \\lfith qrga.YJising .such a project
is in it 1 s timing. The project would have to be undertaken
after rciins il.'e-re S\\lfficient'" to cause fl reusonable amt.>u!"?t of
flO\\lf in the river. At such a tirae, clu1nps of \\•.reed to'1.'ed 8.itJay
from the river banks and out of creeks, \\•:ould be carried out
to sea.
LI. DISCUSSION
The control of ~xcessive growths of aquatic plants is difficult;
much more so than the control of terrestrial >reeds. The use of
chemicals on aquatic it!eeds is costly and the aquatic environment
may be put at risk. Any adverse effects are not likely to be as
•
l
localised as they are in the use of herbicides on land.
The use of sophisticated machines is also correspondingly more
difficult on or near water. The cost of building anrl using such
machines to harvest aquatic weeds may be amortised by using the
weeds in some way, The water hyacinth can be used as stock food,
fertilizer or in the manufacture of paper (Nat. Academy of Sciences,
1976). Research is also being carried out on the possible use of
the hyacinth in generating gas for industrial or domestic use
(H. Solly. personal communication).
