Effects of entomopathogenic fungus and spider plant intercrop in control of onion thrips and iris yellow spot virus

Abstract

Iris yellow spot virus (IYSV) is a major constraint to bulb onions production in Kenya. In search for alternative to synthetic insecticide, field experiments were conducted for two cropping seasons to evaluate the effectiveness of spider plant intercrop, Metarhizium anisopliae and carbonsulfan insecticide in the management of onion thrips and IYSV. Two onion varieties; Bombay red and Red creole were used. Randomized complete block design in a split plot arrangements was adopted. Results showed both varieties treated with entomopathogenic fungus recorded the least number of adult thrips while insecticide treated plots recorded the least larvae thrips. Insecticide, entomopathogenic fungus and intercrop significantly reduced IYSV incidence as compared to the control plots. Bombay red variety treated with fungus recorded the lowest severity and virus titer levels in the two cropping seasons. Adult thrips positively correlated with IYSV incidence in season one (r = 0.575; P <0.001) and two (r = 0.580; P <0.001). Red Creole treated with insecticide recorded the highest bulb onion total yield (10782.8 T/ha) and marketable yield yield (8314.8 T/ha) in the first cropping season. Entomopathogenic fungus treated plots outweighed other treatments in the second cropping season and recorded total bulb yield of 8503.7 T/ha and marketable yield of 7611.1 T/ha. Although, spider plant intercrop reduced bulb yield in both seasons, it contributed significantly in reducing onion adult thrips and increased food productivity. Metarhizium anisopliae and spider plant intercrops were found to be effective bio-pesticide and we suggest their inclusion in the integrated management strategies of vector thrips and IYSV.