Pest management in tropical vegetable systems in cucurbit crops

Cucurbit crops are prone to attack by a number of sap-sucking insect pests, including silverleaf whitefly (SLW) and aphids. These pests have the potential to cause devastating and irreversible damage to the $1.5 billion Australian horticulture industry. This project investigated a number of potential management strategies. An efficient and accurate sampling method was established to assess harmful and beneficial insects in both organic and conventional cucurbit farms. The relationships between SLW and selected biotic and abiotic parameters were investigated. In particular the role of weather, predators and alternative hosts was documented. Lastly a range of alternative control strategies was investigated. SLW numbers increased as maximum temperature and relative humidity 3- 4 weeks prior to sampling increased. Therefore, periods of increased temperature and relative humidity may provide a warning to vegetable growers of a potential SLW outbreak in 3-4 weeks, allowing growers to take necessary precautions. Alternative control strategies, such as the use of the soft pesticide, Pyriproxyfen, an insect growth regulator, returned beneficial results including reduced SLW numbers, reduced fruit damage and increased yield and fruit quality. Floating Row Covers were also found to reduce numbers of SLW and fruit damage, and to increase yield. The use of companion plants for habitat manipulation was also investigated. Plantings of Lablab hosted the highest numbers of beneficial insects, followed by Good Bug Mix. Lucerne and Niger not only showed little promise in hosting beneficial insects but also hosted significantly more of the harmful insects. Of the potential alternative hosts assessed, pumpkin, capsicum and eggplant hosted the greatest numbers of SLW, whilst pigweed hosted almost none. Compared to the conventional farm, crops on the organic farm had more predators (ladybird beetles, lacewings and spiders) and fewer SLW and aphids probably due to the absence of use of conventional and broad-spectrum insecticides. These results demonstrated the feasibility of alternative control strategies.

Submission note: A thesis submitted in total fulfilment of the requirements for the degree of Doctor of Philosophy to the School of Molecular Sciences, College of Science, Health and Engineering, La Trobe University, Bundoora.

Thesis with publications.