Abstract:

The study was carried out on-station at Ngetta Zonal Agricultural Research and Development
Institute (Ngetta-ZARDI), in mid-northern agro-ecological zone of Uganda to establish the effect
of synthetic and natural pesticides on insect pests and natural enemies in citrus orchards. Neem
leaf extract, a natural pesticide and dimethoate, a synthetic pesticide, were used. Three different
levels of concentration were used for each pesticide. For Neem leaf extract 1 liter of neem leaf
extract per 10 liters of water, (neem 1:10), 2 liters of neem leaf extract per 10 liters of waler
(neem 2:10) and 5 liters of neem leaf extract per 10 liters of water (neem 5:10) were used. For
dimethoate 0.001 litres of dimethoate per litre of water (dim 1:1), 0.002 litres of dimethoate per
litre of water (dim 2:1), and 0.003 litres of dimethoate per litre of water (dim 3:1) were used.
These formed 6 experimental treatments and were applied on five citrus plants in a plot at an
interval of 3 weeks. The experimental design used was randomized complete block design
(RCBD) with 3 blocks, each composed of 7 plots replicated three times, with 6 treatments and a
control. Natural enemies’ population and pests’ damage were recorded before applying
pesticides. Six common pests, aphids, scales, leaf miners, orange dog, mealybugs and citrus
wooly whitefly were recorded, while four natural enemies, wasps, spider, ladybird and preying
mantis were observed on citrus. Severity of infestation was on a scale of 0 to 5, where: 0= no
pest damage seen (0% infestation); l=very low pests damage (1-15% infestation); 2= low pests
damage (16-34% infestation); 3= moderate pests damage (35-59 infestation); 4 = high pest
damage 60-70% infestation; 5= very high pest damage (71-100%). Results indicated significant
difference (P< 0.05) in leaf miner severity in neem and dimethoate treatments as well as the
control. Significant difference also existed between neem treatment and control. However,
results did not show significant effect (P>0.05) of pesticides on natural enemies prevalence but
siginificant effect occurred between treatment levels. Spiders and preying mantis population was
significantly affected by neem 1:10 and neem 5:10. Dimethoate application had significant effect
on preying mantis population at 2:1 level. This shows that both neem and dimethoate have
substances that can kill living organisms/insects. The study indicated that there was significant
difference in pests severity between blocks but no significant difference in natural enemies’
population existed between blocks. Both natural enemies and insect pests showed significant
difference in population and severity respectively, between the experimental plots. Rainfall and
temperature had significant effect on the population and activity of both insect pests and natural
enemies in the citrus orchard. In general the experiment found out that natural enemies and insect
pests have response to different pesticide concentration levels. For effective insect pest
management in citrus some recommendations are presented in this report.