REGIONAL LAKE VICTORIA WATER HYACINTH MANAGEMENT
PROGRAM
James
.A. Ogwang, Ph.D
National
Agricultural Research Organisation
Biological
Control of Insects and Weeds
Namulonge
Agricultural Research Institute
P.O
Box 7084,
Kampala
- Uganda
Kampala, February 17th 2002
Aquatic ecology has of late become of a major
importance in the East African region (Uganda, Kenya, Tanzania, Rwanda and
Burundi). This rather sudden development is partly due to the appearance and
associated negative impacts of water hyacinth on the livelihood of the people
that dwell in the L. Victoria basin and its catchment. Water hyacinth gained
importance as an aquatic weed in 1989 when it was first noticed in
L. Victoria. Prior to this, the weed was earlier noticed in the Ugandan inland
Lake Kyoga in 1987 (Twongo pers. com).
Rwanda
and Burundi with their hilly surrounding are believed to be the main source of
water hyacinth that infests Lake Victoria. This is because water hyacinth
infestation points occur along the many small streams from the Rwanda and
Burundi highlands. From these infestation points, water hyacinth eventually
enters L. Victoria via R. Kagera that flows through Rwanda, Tanzania and
eventually Uganda.
At
its peak of infestation, water hyacinth covered an estimated 12,000 ha of L.
Victoria shoreline of Kenya, Tanzania and Uganda thus creating problems for the
lake side residents (Nkuba, 1997; Twongo, 1996). Problems associated with this,
among others, included obstruction of both urban and rural water intake points,
reduced fishing and hence fish export disease hazards and reduced industrial
output due to frequent interference with hydropower generation. It became urgent
that a solution be found to combat this menace. Environmental Impact Assessment
was carried out, mechanical and biological control methods were approved, and
while herbicide control was deferred pending further studies. Hence, a combined
effort of both mechanical and mainly biological control was used and this
reduced the weed biomass by an estimated 80% within a period of about four years
(Ogwang and Molo, 2000). Some reduction could be attributable to pathogenic
attacks and other environmental factors like wind which influences wave action.
It was recognised by the governments of Uganda, Tanzania, Kenya and Rwanda that the weed problem needed attention in the upper River Kagera watershed. Resurgence from (existing Lake sources) and masses of water hyacinth arriving via R. Kagera would remain a long-term source and problem of water hyacinth in L. Victoria.
Uganda
and Rwanda signed a Memorandum of Understanding to co-operate in common
agricultural issues that included water hyacinth control. Clean Lakes Inc.
through the Regional Lake Victoria Water Hyacinth Control Program supported by
United States Agency for International Development (USAID) initiated a
biological control program in Rwanda. This was in co-operation with Institut des
Science Agronomique du Rwanda (ISAR) to tackle the problem of water hyacinth
from high in the Kagera River basin watershed. This is a program executed
through a planned scheme of activities that started with the training of Rwanda
and Burundi nationals on biological control of water hyacinth in Kampala in
1999. The training was followed by the set up of weevil rearing facilities at
Karama (Sept 2000), Ruhengeri, and near Lake Ihema
(Akagera National Park) in July 2000 to facilitate their releases and
spread of the weevils in Rwanda.
All
operations of biological control activities in Rwanda were a collaborative
effort by the National Agricultural Research Organisation (NARO) of Uganda,
Institut des Sciences et Agronomique du Rwanda
(ISAR) of Rwanda and Clean Lakes Inc.
Additionally,
the United States Geological Survey assisted with images to support the
documentation of weevil releases and future impact on the weed biomass. Clean
Lakes Inc. supported field trips by members of the water hyacinth Unit (MAAIF)
to Rwanda that resulted in a number of recommendations. This also included
identification of weevil rearing site locations, construction of weevil rearing
facilities and other activities.
Against
the above background Clean Lakes Inc. hired my services to Rwanda to Conduct
Water hyacinth and Biological Control monitoring and Training
between 3-9 February 2002. Specific tasks were as follows:
- Monitoring water hyacinth/ weevils at Ruhengeri, Gashora, Rusumo and L. Mihindi
-
Visit weevil rearing facilities at Ruhengeri, Gashora and L. Ihema
-
Provide field training and advice to the ISAR biological control
Implementers
-
Provide
constraints/recommendations
Monitoring is an important tool that quantifies the establishment and what impact, if any, that a natural enemy is having on a target pest. Consequently, monitoring, establishment, and impact are vital as it reveals any need for change of strategy in weevil use for water hyacinth control.
Based
on the above and as per TOR, weevil monitoring was conducted at Ruhengeri,
Gashora and L. Mihindi and Rusumo.
Dr
J.A. Ogwang, a scientist from NARO, Mr Patrick Agaba from Clean Lakes Inc., Mr.
Freddie Gashamura, a technician from ISAR, Karama, and Evariste from ISAR,
Butare conducted weevil monitoring at Kamira Bridge on River Mukungwa. Mr.
Asiimwe, a scientist from ISAR, Butare and in charge of Water Hyacinth
Biological Control Program in Rwanda was not yet in Kigali and so could not join
us. At the bridge we hired two labourers to collect water hyacinth from sample
points, these were Mr. Daniel Nkundabanyanga and Mr. Fidel Habyarimana. In
addition to sampling, about 50 awareness posters were distributed at the bridge
to very enthusiastic villagers.
Six
samples were taken from along the shores of Kamira bridge location. Two
samples were taken at the northern part of the bridge while four were taken
downstream on the Southern side of the bridge.
During
sampling,
a 0.5 x 0.5-m wooden quadrant was tossed on the water hyacinth mats that were
mostly anchored on the shoreline. All plants enclosed within the quadrant were
collected and counted. Total plants and ramets were similarly counted and
recorded. Prior to counting the collected plants were placed inside a gunny bag
and weighed. It was not possible to weigh individual plants, as the weighing
scale was not sensitive enough. Ten plants were then randomly selected from the
collected plants and the following parameters recorded:
-
leaf
area of the second youngest petiole
-
number
of weevil feeding scars on the leaf on the second youngest petiole
-
total
number of weevils found on the sampled plant
-
petiole
length of the second youngest plant
-
Root
length
-
Geographical
location of the sampling point (where possible).
The
plant parameters were measured following standard procedure developed by CSIRO
and modified by Clean Lakes Inc. (laminated graph paper for measuring the leaf
surface area in the field).
Table 1 (a). Mean number of weevils and water
hyacinth parameters per ten plants sampled at Ruhengeri
Date: 5-
2- 02
Location: Kamira Bridge
Sample *Total No. of *Total No. of weevil Root No of Petiole Leaf
No.
plants/
ramets/
No./10
length/
scars/ length
Area
quadrant
quadrate
plants 10 plants
sample
leaf
1
14
26
0.2
33.6
4.1
28.7
81.8
2
16
27
0
37.9
0
21.7
44.9
3
9
13
0
30.3
1.3
52.9
130.5
4
4
8
0
31.8
0
48
97
5
5
10
0
34.9
0
60.2
106.8
6
6
12
0
27.8
0
40.4
107.5
* Note that these refer to TOTAL but not Mean numbers per quadrant
Table 1 (b) Geographical Positioning System Information for sample sites
at Kamira Bridge, Ruhengeri
Sample
number
Position
Altitude
1
S01O 33213
1642m
E0290 38661
2
3 S01O 33210
1639m
E0290 38655
5
S01O 33300
1640m
E0290 38626
6
S01O 33290
1640m
E0290 38622
Generally weevil population is low but indications
are that this will build up over time. It was noted that the waters of R.
Mukungwa are moderately turbid and large healthy plants were seen floating
downstream. This indicates that there must be points upstream colonised by large
mats of water hyacinth. There were weevil feeding marks noted on plants at the
Kigali/Ruhengeri Bridge and is
evidence that weevils are established at a point about 1.5km from the highest
point of water hyacinth infestation in the Ruhengeri highlands.
Weevil
monitoring was conducted at four points along the shores of the Akagera River
upstream Rusumo Falls instead of six due to lack of a boat for collection of the
remaining two samples. This was because of logistics as the boat owners the we
were using diverted the boat we were using to other activities. The sampling
team consisted of Ogwang, Agaba, Asiimwe, Gashamura and Evariste.
Mr.
Thomas Singiranabo and Gerald Havugimana assisted the team.
Three
samples were taken from along the shores of River Akagera 200m upstream of
Rusumo Bridge. All Three samples were taken along the Rivers northern bank.
The southern bank falls in Tanzania territory. Sample methods are as described
in pages 5 and six.
Table 2(a) . Mean number of weevils and water
hyacinth parameters per ten plants sampled Rusumo.
Date: 6-
2- 02
Location: Rusumo
Sample *Total No. of *Total No. of weevil Root No of Petiole Leaf
No.
plants/
ramets/
No/10.
Length/ scars/
length Area
quadrate
quadrate
plants
10 plant
sample
leaf
1
18
30
0
38
0
31.1
60.5
2
7
19
0
44.8
0
46.3
105.3
3
12
92
0
29.8
0
25.8
130.5
* Note that these refer to TOTAL but not Mean
numbers per quadrant
Table 2 (b) Geographical Positioning System Information for sample sites
at Rusumo
Sample
number
Position
Altitude
1 S02O 23087 1322m
E030 23774
2
S02O 23144 1323m
E030 46784
3
S02O 23069
1325m
E030 46787
During data collection, not a single weevil feeding
scar was observed on water hyacinth plants at Rusumo (Table 2). This contrasts
with reports by KAEMP that thousands of weevils were released into Kagera from
the Tanzanian side. Very large mats of water hyacinth were seen floating
downstream but none had any sign of weevil feeding scars.
However, observations from Karuma bridge in Uganda
indicates that weevils can survive such powerful falls since no weevils were
released in L. Albert but weevils managed to reach the lakes, establish and had
an impact on the weed biomass. Weevils should therefore be continuously released
despite the power of the Rusumo Falls. This however may not necessarily be the
same as the points of weevil releases are too close to the powerful Rusumo
Falls.
Weevil monitoring at Lake Mihindi
Introduction
The weevil monitoring team here consisted of Ogwang,
Agaba, Asiimwe, Gashamura and Evariste. Six samples were taken on six sites on a
large resident patch of water hyacinth. The Lake had extensive mobile water
hyacinth mats floating freely in the lake. All samples taken had no feeding
marks or any adult weevils. Driving through the Akagera Park from L. Ihema was
tedious due to tsetse flies.
Methodology
All
the six samples were taken form a large
resident patch of water hyacinth. Sampling protocol was as described in pages
five and six.
Results
of parameters taken are shown in Tables 3(a) and (b).
Table 3(a) Mean
number of weevils and water hyacinth parameters per ten plants sampled at Lake
Mihindi
Date: 7-
2- 02
Location: Lake Mihindi
Sample *Total No. of *Total No. of weevil Root No of Petiole Leaf
No.
plants/
ramets/
No/10. Length/
scars/
length Area
quadrate
quadrate
plants 10 plants sample
leaf
1
14
26
0
32.3
0
27.3
54.7
2
16
25
0
61
0
29.3
62.7
3
19
23
0
24.3
0
26.2
46.7
4
13
16
0
43.5
0
45.2
92
5
13
22
0
49.5
0
26.5
50.9
6
16
37
0
32.7
0
66.7
64.3
*Note that these refer to TOTAL but not Mean
numbers per quadrant
Table 3 (b) Geographical Positioning System Information for sample sites
at Lake Mihindi
Sample
number
Position
Altitude
1 S01O 32312 1293m
E030 42647
2
S01O 32311 1291m
E030 42647
3
S01O 32317
1294m
E030 42649
5
S01O 32313
1288m
E030 42647
6
S01O 32331
1297m
E030 42647
Virtually
all the plants sampled were very healthy with no feeding marks. Neither were any
adult weevils recovered from all the plants sampled. There was plenty of
floating water hyacinth mats on the lake especially on the western part of the
lake. Weevil releases have been made at the site of monitoring. Despite no
weevils nor feeding scars being found during this exercise it is expected that
establishment and distribution is starting to take place.
The
team that conducted the final data collection in this assignment was made of
Ogwang, Agaba, Asiimwe, Gashamura, and Evariste. Jean Baptiste Habyarimana and
Fidel Nsanze assisted the team.The exercise was conducted on the Gashora Bridge
on River Nyabarongo.
The
river water was clearer and cleaner than what was seen during a visit here in
December 2001. There was healthy looking water hyacinth at the bridge with a
large mat on the northern part of the bridge having mostly flowering water
hyacinth. The canals also had a lot of healthy water hyacinth.
Six
samples were taken from along the shores of River Nyabarongo bridge location.
Three samples were taken at the northern part of the bridge while the other
three were taken downstream on the
Southern side of the bridge. Sampling protocol used was as described in pages 5
and 6.
Table 4(a). Mean number of
weevils and water hyacinth parameters per ten plants sampled at Gashora Bridge
Date: 8-
2- 02
Location: Gashora
Bridge
Sample Total No. of *Total No. of *Weevil Root No of Petiole Leaf
No.
plants/
ramets/
No./10
length/
scars/ length
Area
quadrate
quadrate
plants
10 plants sample
leaf
1
16
53.5
0
33.6
12.1
21.7
41.1
2
6
14
0
40.8
1.1
41.4
90.3
3
8
21
0
42.8 6.6
22.3
55.7
4
6
53.7
0
25.7
0.3
25.7
54.7
5 11 25 &nbs