By Francis Ndungu
A farmer in Nyandarua County has doubled his cauliflower and broccoli yields by intercropping with fennel to repel aphids, whiteflies, and caterpillars, which are the top cause of economic losses in East African farming, according to researchers.
Aphids and whiteflies suck sap from under leaves and inside buds, with studies finding they destroy 30% to 70% of the region’s brassica crops.
For Samuel Mwangi Mwihaki, based in Ol Jororok, finding a natural cure was a coincidence after he tried a new crop, but it has liberated his farm from years of losses.
“The moment the aphids invaded my cauliflower plantation they became very hard to control, which sometimes forced me to abandon and do away with the whole plantation. In 2022, aphids ambushed my crops and their population outweighed the pesticides and I had to leave the whole plantation to my cattles to feed on, which was a big loss,” he said.
“When the pesticides failed, I tried washing the crops vigorously using water with a lot of pressure, as advised by a friend, but the aphids were only washed away and the plants fell down. Later, they climbed back onto the plant and caused the same harm to my cauliflowers.”
“It was also difficult to balance between having produce with aphids and having no pesticides residuals. I used to spray my crops once per week and sometimes twice when aphids and white flies became severe. When the vet saw me in his agrovet he would automatically know that I wanted pesticides for aphids and white flies even before I said anything.”
But pests develop resistance to repeated pesticide use. “It was not a surprise to see that the pesticide began failing to work . And sometimes, I was using so much I got chemical burn on my crops,” Sam said.
Across the burn, reduced-size cauliflowers, and frequent presence of pests, most of his crops were being rejected by buyers.
Then, in 2023, Sam went to a training seminar that introduced him to a new crop, fennel, which he had not heard of before. The crop is popular in Arab cuisine, where both the bulbs and leaves are eaten. It can also be used for animal feed, and has medicinal properties for humans, lowering blood pressure.
“In the training, I was given five fennel seedlings.” With no other available space, he planted the fennel next to his cauliflowers.
“After two months, scouting of my crops to determine whether to spray pesticides, I noticed the aphids and whiteflies were increasing even after spraying the previous week. But around the fennel plants, there were no aphids, whiteflies, or.”
“In the next planting season, I bought a 10-gram sachet of fennel seeds at Sh500 and planted them alongside the cauliflowers. As the plants emerged after three weeks, I proved the previous observation right with no aphids, whiteflies or caterpillars infested around where the fennel plants were planted.”
Fennel emits a strong scent that deters a wide range of pests, with studies from the International Centre of Insect Physiology and Ecology (icipe) confirming that it is one of several aromatic plants that repel insect pests while attracting pollinators.
“I adopted the intercropping method where I plant cauliflower together with fennel plants. Fennel protects cauliflower from pests and takes long to mature. It also does well in the market since it is sold at Sh200–400 per kilogram depending on supply,” said Sam.
“After every five beds of cauliflower, I now plant one bed of fennel. I also plant fennel around the edges of the cauliflower plantation.”
“When I started using fennel plants as pest repellent it really boosted my cauliflower production as well as broccoli. Initially, in half an acre of cauliflower I used to harvest 4–6 tonnes, but after adopting the method, production increased to 8–12 tonnes. The rejection of my produce reduced by 70%, which was as a result of reduced infestation of aphids, whiteflies, caterpillars, chemical burn, downy mildew and black rot,” he said.
Related News:
Scientists make it cheaper to confuse & prevent crop pests
Plantwise plant clinics helps Kenyan farmers grow more and lose less to crop pests and diseases
Free e-learning course trains farmers to tackle crop pest increasing yields
Sam still uses copper-based fungicides to control black rot and downy mildew, especially during the rainy season. But the fennel has solved his insect problem.
Moreover, “both crops—cauliflower and fennel—do well in the market, but fennel is more profitable, despite it being a pest repellent, making it more valuable and useful as it reduces the cost of production,” he said.
The fennel has helped helped his profits in other ways. Cauliflower prices can vary between Sh100 and Sh150, so reducing the production costs by saving on expensive pesticide costs has made his profits more certain. Plus “growing fennel is cheap since it is not attacked by most of the pests as compared to other crops,” he said.
“I also now repel the pests on other crops in my farm with fennel, planting it together with my red cabbages, lettuce and broccoli.”