Abstract:
Kale production in many parts of the world is mainly faced by the challenge of pests and diseases.
Aphids are a major concern because they make the kales unsightly, reduce their quality, and vector
several diseases. Farmers have over the years relied on chemical sprays to successfully control
these aphids. The chemicals have however led to environmental pollution. Botanical control
methods can be used to replace these chemicals in an attempt to promote environmental
sustainability. The effect of various combinations of garlic (Allium vineale), hot pepper (Capsicum
frutescens) and soap spray on green aphid population on kales was assessed in a greenhouse at
University of Embu. The experiment included eight different treatments: 1.) Hot pepper spray 2.)
Garlic spray 3.) Hot pepper and garlic spray 4.) Hot pepper and soap spray 5.) Soap and garlic
spray 6.) Soap, garlic and hot pepper spray 7.) Chemical spray (Thiamethoxam 250g/kg) was used
as a standard check 8.) Untreated plants were used as control. The experimental layout used was
the Randomized Complete Block Design (RCBD). The experiment had eight experimental rows
including the control. Each row consisted of ten planting bags. The experiment was replicated
thrice. Kales were planted in planting bags and aphids allowed to infest the plants for three weeks
before spraying began. Spraying was done twice; first spraying was three weeks after aphids were
noticed, and second spraying five days after the first spraying. Data on the number of aphids on
kale plants was collected just before spraying and twenty four hours after spraying. Of the botanical
sprays, the soap-hot pepper spray showed a consistently higher reduction in number of aphids,
followed by the soap-pepper-garlic combination, pepper spray, soap-garlic spray, pepper-garlic
spray and garlic spray respectively. The rows that received the chemical treatment had the best
overall reduction in aphid populations, whereas the control experiments always had varying
number of aphids. Neither the chemical nor the botanical sprays showed any form of phytotoxicity
on the kale plants. All treatments applied showed a significant (p < 0.001) reduction in kale aphid
populations both in the first and the second treatment applications. It may be conclude that both
pepper and garlic extracts are effective in the control of green aphids in kales, but their activity is
increased by the addition of biodegradable potassium-based soap. It is recommended that the
research should be repeated using different rates of the botanical extracts
