Commercial-scale field studies were conducted in citrus orchards to test the efficacy of entomopathogenic nematodes (EPNs) in controlling the soil-dwelling life stages of the key pest, Thaumatotibia ...leucotreta. Trials were conducted in three provinces of South Africa from 2011 to 2013. Two EPN species were tested: Heterorhabditis bacteriophora and Steinernema feltiae. Both EPN species were applied underneath citrus tree canopies, either with a spray machine or through the microsprinkler irrigation system. The concentration of nematodes and frequency of application varied. Efficacy of these treatments was measured by evaluation of EPN infection of sentinel T. leucotreta larvae in the soil at various intervals after application and by T. leucotreta infestation of fruit. Successful control was recorded in several trials, with EPN infection of larvae frequently reaching 80 %. However, in a few trials, this level of infection was assisted by naturally occurring EPNs. Fruit infestation by T. leucotreta larvae was reduced by up to 88 %. Efficacy appeared to be limited by suboptimal soil moisture and temperature. The former was influenced mainly by mode and relative thoroughness of irrigation before and after EPN application. This was best obtained through microsprinkler application. Nematode species and concentration also influenced efficacy. Both EPN species survived and persisted in the soil of the treated orchards for up to 4 months. Promising results support their potential for use in an integrated pest management programme in citrus in South Africa.
•Thaumatotibia leucotreta is an important pest of citrus in sub-Saharan Africa.•Heterorhabditis bacteriophora and Steinernema feltiae are virulent to T. leucotreta.•In field trials, more than 80 % of T. leucotreta larvae were infected with nematodes.•Fruit infestation with T. leucotreta larvae was reduced by up to 88 %.•Best results were achieved with monthly applications of EPNs for four months.
