Efficacy Of Leaf Extracts Of Artemisia Annua And Thevetia Peruviana Against Aphis Fabae And Non-Target Organisms On Solanum Scabrum

ABSTRACT

African nightshade (Solanum scabrum Miller) is a vegetable, widely distributed

throughout the tropics including East Africa. It is an important vegetable in Kenya but

consumer demands have not been met due to low yields and partly due to attack by

Aphis fabae Scopoli. The aphids cause serious damage through sucking plant cell sap

from phloem leaving the plant weakened, dehydrated, stunted in growth and eventually

under heavy infestation the leaves curl making the vegetables unattractive to consumers.

Synthetic insecticides have been used but the aphids developed resistance. They are also

a risk to human health and they kill important non-target organisms e.g. predators,

parasites and pollinators. These reasons have led to the quest for use of extracts from

plants to control aphids. The objective of this study was to evaluate the efficacy of leaf

extracts of Artemisia annua Linn. and Thevetia peruviana (Pers.) Schumann for the

control of A. fabae infesting S. scabrum, its yield output and impact of extracts on nontarget

organisms during short and long rain season from September to December 2015

and from March to July, 2016 respectively. Field experiments were carried out in

Masinde Muliro University of Science and Technology’s Main Campus farm. A

randomized complete block design (RCBD) of six treatments and three replicates was

used. The treatments used were A. annua 0.5%, A. annua 1%, T. peruviana 0.15%, T.

peruviana 0.3%, Albaz 10 EC insecticide and water. The African nightshade (S.

scabrum) used as test crop and seeds were obtained from Kenya Seed Company. A.

annua and T. peruviana leaves were each obtained from two farm each. The S. scabrum

plants were sprayed thrice at an interval of two weeks. Parameters collected were A.

fabae population density, leaf damage caused by aphids, plant height (cm), leaf width

(cm), number of flowered plants per plot, number of plants with formed fruits per plot,

number of plants with ripened fruits per plot and total weight of fresh and dry leaves,

stems and seeds (Kgs) per plot and diversity of non-target organisms. Results showed

that leaf extracts of A. annua 1% concentration significantly (p< 0.0001) reduced the

aphid population density, had significantly higher mean weight per plot of dry leaves

(0.60, 0.63 kg per plot), stems (2.62, 2.97 kg per plot) and seeds (1.36, 1.57 kg per plot)

and lower number of damaged leaves per plot (24.67, 15.00) for short and long rains

respectively. Leaf extracts of A. annua 0.5% concentration had significantly (p< 0.0001)

the highest aphid population density per plot, the lowest mean weight per plot of dry

leaves (0.38, 0.41 kg per plot), stems (1.82, 1.91 kg per plot) and seeds (0.92, 1.07 kg

per plot) and highest number of damaged leaves per plot (49.33, 36) for short and long

rains respectively when compared to those treated with leaf extracts. Plots treated with

leaf extracts of A. annua 0.5% and T. peruviana 0.15% recorded higher population of

bees, beetles and black ants. Plots treated with leaf extracts of A. annua 1% and T.

peruviana 0.3% recorded lower population of bees, beetles and black ants. The results of

this study indicated that leaf extracts of T. peruviana 0.3% and A. annua 1% had the

potential to for control of A. fabae infesting S. scabrum while leaf extracts of A. annua

0.5% and T. peruviana 0.15% conserved non-target organisms.