A Dissertation Submitted in Partial Fulfillment of the Requirements for the Degree of
Doctor of Philosophy in Life Sciences of the Nelson Mandela African Institution of
Science and Technology
For smallholder farmers, suitable plants for pest management and as foliar feed are obtained
with ease, and when successfully exploited, could contribute to local income generation
through commercialization. However, with extensive research on their efficacy, toxicity and
availability, the use of plant extracts is not widely adopted especially for smallholder farmers
in rural settings. This study focused on evaluating factors that can foster extensive use of
plant extracts among smallholder farmers. Questionnaires and focus group discussion were
used to assess the perception of farmers towards using pesticidal plants, highlighting possible
challenges, benefits and future enabling aspects for sustainable bean crop production. Plots of
5m
2
were established by farmers where an evaluation of the efficacy of Tephrosia vogelii,
Tithonia diversifolia and Lantana camara was done to ascertain their potential for common
bean insect pest management and impacts on beneficial arthropods. Additionally, the study
evaluated spatio-temporal variability in bioactive phytochemicals of the most effective plant
(T. vogelii), as well as the contribution of T. vogelii and T. diversifolia towards growth promotion
and yield of common beans. Results showed that high per cent (99%, n=67) of
smallholder farmers had pest challenge and that only (39.7%, n= 27) reported using plant extracts.
Likewise, farmers reported a lack of working tools and motivation from researchers
and extension officers as a challenge hindering the use of plant extracts. Plant extracts
showed efficacy in pest management compared with untreated control whereby T. vogelii
significantly reduced abundance of aphids (0.06 ± 0.02) and foliage beetles (0.17±0.03 compared
with
untreated
(0.4
±
0.05
and
0.5
±
0.04
respectively).
Again,
the
increased
grain
yield
was
recorded on plots treated with T. vogelii (3.8 ± 0.23) and T. diversifolia (3.3 ± 0.23)
compared with untreated beans (1.5 ± 0.16), when applied as a foliar spray (2.7 ± 0.20) compared
with
soil
drench
(2.1
±
0.16).
Phytochemical
variation
was
noted
in
T.
vogelii
where
an
additional
chemotype 3 was first recorded. Hence, under smallholder farming conditions,
plant extracts can contribute to sustainable bean crop production if practical implementation
that involves smallholder farmers is a priority.