dc.description.abstract | Breeding has significantly improved drought tolerance in green gram but marked yield losses
continue to emanate from field pest’s damage. Important pests of green gram are pod borers,
Maruca testutalis (Geyer), aphids, Aphis gossypii (Glover) and whiteflies, Bemisia tabaci
(Gennadius). Management of these pests has partly been constrained by the limited understanding
of crop traits that modulate their infestation. Continuous use of synthetic pesticides causes serious
health and environmental consequences. To reduce these challenges, and lower the cost of
production, farmers rely on indigenous knowledge to manage crop pests. Several plant species are
known to have insecticidal properties against a range of insect pest. Despite growth on research,
there is limited data on pesticidal plants and only a few of them have been commercialized for pest
management hence remaining a small but growing component in crop protection. Field
experiments were conducted in southeastern Kenya to evaluate a collection of old and new green
gram varieties for tolerance to field pests, and to identify traits that confer resistance for objective
one. The old varieties were KS20 and N26, both released in 1990s whereas the modern counterparts
were Biashara, Karembo and Ndengu-Tosha. Evaluating the efficacy of four plant extracts of
diverse species, including neem (Azadirachta indica), melia (Melia volkensii), tick berry (Lantana
camara) and garlic (Allium sativum) in the management of green gram field pests was also studied.
Respective plant extracts were prepared and applied at 10mL/20L of water at seven days interval
and compared to lambda-cyhalothrin which was applied at the rate of 5mL/20L of water as a
standard check and untreated control. Results showed significant differences amongthe varieties in
maturity, leaf area, leaf hair density, leaf moisture content and pod wall thickness. Earliness
significantly reduced pest infestation, whereby KS20 matured early while N26 was late,and the
new varieties were intermediate. Leaf area (R2 = 0.52) and leaf moisture content (R2 = 0.71)
positively correlated with pest infestation while leaf hair density (R2 = 0.47) and pod wall thickness
(R2 = 0.58) showed a negative association with pod borer and aphid counts. Crops applied with tick
berry and melia plant extracts showed significantly higher number of pod borers,aphids, whiteflies
and natural enemies of about 70 -80% compared to neem and garlic which showed 40-50% of the
pest numbers. Pod damage was highest in melia and tick berry ranging from 70-90% and lowest in
neem and garlic with a range of 36 -63% accordingly. Crops sprayed with garlic extract out-yielded
(2.8 t/ha) the other treatments while those applied with melia recorded the least grain yield (2.6
t/ha). However, objective one results did not reveal any particular traitsthat associated with either
the old or new varieties, which implied that breeding of green gram in Kenya has not selected for
tolerance to field pests. Nonetheless, green gram breeding programs could select for early maturity,
open plant canopy, pubescent leaves and thicker pod walls to reduce field pests’ infestation. On
objective two, the four plant extracts offered an effective control of keypest species, especially
neem and garlic extracts, that was comparable in terms of yield harvested to the synthetic pesticide.
Overall, the plant extracts had lower negative impact on the beneficial organisms compared with
the synthetic insecticide. Results of this study imply that integrated field pest management practices
in green gram could deploy varieties with morphological traits that impair pest infestation as well
the incorporation of pesticidal crude plant extracts. | en_US |