Lari farmer uses onions as biopesticide to control aphids

In cut­ting down pesti­cide ap­plic­a­tion and the ac­cru­ing costs in pro­duc­tion, one farmer suc­ceeded in vend­ing off the pests by grow­ing onions around his green­house to­ma­toes in the last sea­son.

Lari Sub-county farmer Nathan Kimeu was im­ple­ment­ing an idea he learnt from the In­ter­net that onions’ smell can repel some crop pests like aph­ids.
“I found out that some crops are good bio­lo­gical con­trols of pests, which at­tack com­mon com­mer­cial foods such as chil­lies, cap­sicum, Kales, cab­bage, to­ma­toes, among oth­ers. I also leant that green­house ro­ta­tion with non-vic­tim crops like cori­ander can break the li­fe­cycle of the en­emies,” he said.
When he grew onions in the peri­phery of his 8m by 30m green­house, which had to­ma­toes as the main crop.
In­deed on close scru­tiny of the to­ma­toes on the out­er­most lanes- those neigh­bour­ing the onion sol­diers- were free from the aphid at­tack for the en­tire sea­son.
Aph­ids are pest that drill into the leaves of crops. They suck the sap with the nu­tri­ents, caus­ing severe pro­duce losses due to un­healthy crops.
The leaves curl to the be­cause of the heavy in­fest­a­tion from the un­der­side. This con­di­tion re­duces the sur­face area for pho­to­syn­thesis, the food mak­ing pro­cess in plants.
Be­cause of the ex­trac­tion of the nu­tri­ent-rich sap, some leaves turn yel­low due to mal­nour­ish­ment, which also re­duces pho­to­syn­thesis res­ult­ing from the ab­sence of the green pig­ment.
This neg­at­ively af­fects the over­all pro­duc­tion.
Ap­plic­a­tion of chem­ic­als in the con­trol of the pests is not only ex­pens­ive as is re­quired in­ter­val in­ter­ven­tions. But the onions are a one-time cost that de­fends the crop until the end of the sea­son and still be sold along­side the main crop, Kimeu said.
“Or­ganic farm­ing is gain­ing fame as food-re­lated dis­eases rise. I am start­ing small and with such pos­it­ive res­ults, I hope to go or­ganic to meet the small but healthy eat­ing mar­ket,” he said.
The Ki­ambu County farmer in­tends to grow the ‘sol­diers’ along the rows of the to­ma­toes to boost the de­fence while re­du­cing the cost of pro­duc­tion.
Al­though he can­not quantify the money saved from the bio­lo­gical con­trol of the pests, the farmer says his main pesti­cides ap­plic­a­tion was spe­cific on other pest such as white flies and mites.

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The to­ma­toes, however, never per­formed well to­wards the peak of har­vest­ing des­pite re­duced at­tack from the pests.
Kimeu at­trib­utes the de­cline to the over­growth of the roots in the bags, which he says, hindered uptke of water and nu­tri­ents. The mul­tiply­ing roosts were scorched by the poly­thene bag, des­pite ap­plic­a­tion of water be­cause of the high tem­per­at­ures dur­ing the dry spell.
The crop pro­tec­tion pro­grammes star­ted from seed­lings age. He grew the seed­ling in a soil­less media which helped in con­trolling other pests like nem­at­odes.
This also gave a strong vigour in growth of the to­ma­toes since there was min­imum dis­turb­ance of the rots dur­ing trans­plant­ing.
He also steamed the soil to kill dis­ease caus­ing patho­gens like nem­at­odes.
“I ex­pec­ted to har­vest at least 30 crates of 32kg per week for eight months. But it never happened. The loss is a gain for me; I have learnt how to do it bet­ter in the next sea­son,” Kimeu said.
Com­mon crop pests such as mites, leaf miners, aph­ids, white flies, among oth­ers do not at­tack cori­ander. This makes it one of the best ro­ta­tional crops after har­vest­ing the sus­cept­ible vari­et­ies. Grow­ing the cori­ander in a green­house breaks the li­fe­cycle of such pests, there­fore re­du­cing their pop­u­la­tion ahead of the next sus­cept­ible crop.