| dc.description.abstract | In Kenya rice is the third most important cereal grain in consumption after maize and wheat
and about 400,000 rice farmers, the majority of them women earn their livelihood out of the
crop's production. However, its production is constrained by both abiotic and biotic factors.
One of the most important biotic constraints is the African white rice stem borer, Maliarpha
separatella Ragonot. Despite the importance of this pest, information on the factors that
influence its distribution, extent of crop losses and management practices in Kenya is scanty.
In addition the level of knowledge that farmers have on this pest is undocumented, hence it is
difficult to gauge its importance from the farmers' perspective. Therefore this study was
carried out; 1) to provide information on socio-cultural and economic factors that influence
distribution and the management of the pest 2) to determine the pest's spatial and temporal
fluctuations 3) to determine the level of F~s6s caused by the pest al1d develop economic
injury levels 4) to evaluate entomopathogenic nematodes against the pest 5) to screen rice
cultivars resistant to the pest 6) to evaluate., the effectiveness of a combination of
entomopathogenic nematodes and resistant ric,e cu.ltivars in the management of the pest. To
meet these objectives a farmer survey was carried out at Mwea irrigation scheme to
investigate factors that limit rice production and the extent of farmers' local knowledge and
management of M separatella. A scheme wide observation trial on the pest was set up at
Mwea irrigation scheme to investigate how the pest fluctuates in the scheme and the factors
that influence this fluctuation. To understand yield losses attributable to the pest, a screen
house experiment was set up at Kenya Agricultural Research Institute, Mwea where rice
plants were artificially infested with M separatella egg batches at early infestation and late
infestation which was 3 and 6 weeks after transplant date (W AT) respectively.
A laboratory experiment was set up to evaluate effective entomopathogenic nematodes
against the pest and field trials on resistant rice cultivars and a combination of these two in
the management of the pest were conducted at the Kenya Agricultural Research Institute
Mwea field testing station. These studies were carried out from February 2010 to July 2011.
The results from the survey indicated that rice cultivation in the scheme was for commercial
purposes. The average age for the majority of farmers (62%) was 42 years. Most the farmers
had about eight years rice farming experience and their main sources of information was from
other farmers. Age, rice farming experience and rice farming as the only occupation, had a
highly positive significant influence on the M separatella knowledge and being a female
significantly increased the probability of not having knowledge of M separatella. The
percentage number of farmers who used pesticides to control M separatella was 77%. About
60% of the respondents indicated that not controlling the pest Fill be too costly for the farmer
in terms of yield losses. Empirical results shbWed that irrigation water provision schedule and
cropping system significantly influenced spatial and temporal fluctuation of M separatella in
the scheme. High pest infestations occurred in areas of sporadic irrigation and where double
cropping of rice was carried out. There were ntil significant differences in pest infestations in
the main season crop and the ratoon crop (p>0;05). The percent number of whiteheads and
tunneled tillers in farms under System for Rice Intensification were not significantly different
from the flood irrigated fields (p>0.05). Maliarpha separatella infestations in the various
planting regimes was independent of water provision (p>0.05). The results from the screen
house experiment showed that maximum yield reduction (91%) occurred to the plants
infested with 8 egg batches in the early infestation. There _w.ere no significant differences in ,
the plants infested with 6 egg batches in the early infestati~n period, from those infested with
8 egg batches in the late infestation (p>0.05).
On the basis of cost benefit ratio, the economic injury level was 6 and 8 egg batches per
square meter of rice plants for early and late infestation respectively. The corresponding
economic threshold level was 4 egg batches/ m2 in the early infestation and 6 egg masses/ m2
in the late infestation.
The entomopathogenic nematode, Heterorhabtidis indica Poinar, Karunaka & David was
found to have significant efficacy on the pest under laboratory conditions (p<O.05).
The rice cultivar M27608 was tolerant to M separatella damage and M27615 was resistant.
Combination of these two cultivars with H indica significantly reduced M separatella
damage (p<O.05). From this study, it can be concluded that knowledge of managing M
separatella infestation at Mwea irrigation scheme is scanty and the farmer's local knowledge
of M separatella influences its management practices. Sporadic water provision and
continuous rice cropping increase M separatella infestation.'>, but ratooning of the rice crop
does not increase the pest infestation. Malz;P:Pha separatella infestation causes reduction in
rice yields and results in substantial economic losses. The management of the pest is possible
by use of a combination of effective entomopathogenic nematodes and resistant rice cultivars. | en |
