Evaluation of selected synthetic insecticides, neem products and border crops in the management of aphids (aphis gossypii) in Okra (abelmoschus esculentus) in Eastern Kenya

Abstract

Studies to evaluate the efficacy of two synthetic insecticides, imidacloprid 350g/1 (Gaucho FS ®) and Lambda- cyhalothrin 17.5g/1 (Karate 1.75 EC ®) and two neem products, 0.15%w/w azadirachtin (Achook®) and 0.6%w/w azadirachtin (Neem extractive®) and a combination of Neem extractive® and Karate® in the management of aphids (Aphis gossypii Glover) in okra (Abelmoschus esculentus L Moench) were conducted in the field during two planting periods of December 2003- March 2004 and February - May 2004 at Kibwezi Irrigation Project in Eastern Kenya. Gaucho was applied, as a seed dressing while the other insecticides were foliar applied. Both the live and the parasitised aphids (mummified aphids) population were monitored on the leaves of ten randomly selected plants per plot for nine weeks. Aphid population was also monitored on ten pods per plot and this was done on weekly basis for seven weeks. Application of pesticides significantly (P<0.05) reduced both live and parasitised aphid population on both the leaves and pods. Imidacloprid (Gaucho®) was the most effective pesticide in reducing aphid population and aphid reduction in the imidacloprid treated plots were 98.2% and 96.4% during the two respective planting periods. Neem products namely Achook® and Neem extractive® compared well in suppressing aphid population in the first planting period. Karate® and a combination of Karate® and Neem extractive® were the least effective treatments and the two were not significantly different in reducing aphid population. Yields were significantly (P<0.05) different among treatments and the imidacloprid treated plots had slightly higher yields than other treated plots. Field experiments were carried out to evaluate four border crops of maize (Zea mays) Sorghum (Sorghum bicolor) pigeon peas (Cajanus cajan) and millet (Pennissetum glaucun) for their effectiveness in the management of aphids in okra. The four border crops were planted fourteen days before the planting of okra. Both live aphid population and parasitised aphids (mummified) were monitored on the leaves of ten randomly selected okra plants per plot for ten weeks. Aphid population was also monitored on ten okra pods from ten randomly selected plants per plot. This was done on weekly basis for seven weeks. Aphid population on okra leaves were significantly (P<0.05) different among the treatments during the two planting periods The pigeon peas bordered plots had lowest mean aphid population of 2530.0 and 2032.0 during the two respective planting periods. Although the pigeon peas border proved to be better in reducing aphid population on leaves, it had no effect on the population of aphids on the pods. The highest aphid population was found in the maize and the fallow-bordered plots during the first and the second planting periods respectively. The maize -bordered plots had the highest number of parasitised aphids during both planting periods (15.6 and 79.3). There were more parasitised aphids in all treatments during the second planting period than during the first one. Yields were not significantly (P>0.05) different among the treatments during both planting periods. The results obtained in this study show that, insecticides made from the neem tree are as effective as the synthetic ones and therefore can be used in the management of aphids in okra production. The study also showed some border crops have the potential to reduce aphid population in okra and therefore they could be considered for use in combination with insecticides to form an integrated pest management strategy in okra production.