Ground Cover Supplement : GC Supplement - Integrated pest management
13 INTEGRATED PEST MANAGEMENT GROUND COVER SOFTER OPTIONS PARASITOID MANAGEMENT TO BEAT SILVERLEAF WHITEFLY Studying the relationship between SLW, crops and a biological control agent is leading to more detailed control strategies By Nancy Schellhorn and Paul De Barro BIOLOGICAL CONTROL IS most effective when the control agent arrives in the crop at the same time as, or shortly after, the pest, thus slowing pest population build-up. Silverleaf whitefly (SLW) is a pesticide-resistant strain of Bemisia tabaci, which was first detected in Australia in 1994. It is now a widespread pest of horticultural, cotton, grain and legume crops in the northern region. In 2005, CSIRO released the biological control agent Eretmocerus hayati to control SLW in Bundaberg, Queensland. By March 2007, the parasitoid had established and spread more than 30 kilometres from the release point. How the type, number and location of crops that host SLW and parasitoids influence the process of both organisms colonising a new crop and ultimately the control of SLW, was investigated. The following outcomes were from a series of research trials and surveys, predominantly in horticultural crops. However, these findings are considered relevant to broadacre grain legume production. nSLW and the parasitoid, E. hayati, colonised melon seedlings within three days and repeatedly during the 14-day trial. Both were found to travel more than 4km in three and a half days. nSLW is highly mobile: in landscapes with intense crop production and large populations of SLW, the number of SLW host crops in the landscape in a 3km radius explains the proportion of the crop infested, but sources within 100 metres determine the severity of the SLW infestation. nIn landscapes with limited crop production and few SLW, the density of SLW within 100m explains the proportion of a crop that is infested and the severity of the infestation. nE. hayati is also highly mobile, but large numbers will arrive at a crop faster if there is a source nearby (that is, within 100m). SLW quickly finds new seedlings, therefore the implications for SLW management in areas with intense production of SLW susceptible crops (for example, soybean, cotton) is that an area-wide management approach is essential, as well as the implementation of on-farm strategies to suppress populations. In areas with limited numbers of crops susceptible to SLW, growers' on-farm management has the greatest impact. The parasitoid has also been found to be highly mobile. Maintaining a source or refuge within 2km of newly planted crops, and planting the new crop adjacent to an existing crop, results in the best parasitoid colonisation. Again, an area-wide approach for parasitoids, such as a common refuge within 2km of each crop, and insecticides that are soft on the parasitoid, will deliver the best SLW control. To take an area-wide approach to controlling SLW, communities will need to set common goals and common methods of achieving these. Employing a crop agronomist to coordinate such an approach, and to monitor crops across multiple properties, is considered a productive approach to achieving an area-wide solution. The objective is not to eradicate SLW. First, this is not possible; and second, to be successful the biological-control agent requires some SLW to survive. The parasitoid also requires suitable refuges to improve its survival. Refuges for the parasatoid include any plants that host SLW in areas where insecticide is not being used. The softer insecticide options indoxacarb (Steward®) and spinosad (TracerTM) are harmful to parasitoids, as are organophosphates, pyrethroids and carbamates. Insect growth regulators, such as pyriproxifen, and the anti-feeding insecticide pymetrozine are soft options that help control SLW without killing the parastoid. Bacillus thuringiensis (Bt) is fine, as are the Lepidoptera virus products. Neonicatinoids applied as a soil treatment are compatible, but not the foliar treatments. The size, location and timing of plantings of a refuge are unknown, but this is hoped to be the focus of future research. □ GRDC Research Code CSE00028, CSE00046 More information: on the study -- Dr Nancy Schellhorn, 07 3214 2721, firstname.lastname@example.org; on the release of E. hayati -- Dr Paul De Barro, 07 3214 2811, email@example.com What is a parasitoid? Parasites are organisms that feed on the body of another -- the host. Some eventually kill their host and become free-living as an adult, these are called parasitoids. AREAS OF SLW SUSCEPTIBLE CROPS REQUIRE AN AREA-WIDE MANAGEMENT APPROACH PHOTOS: PAUL DE BARRO (Above left) Silverleaf whitefly (SLW) nymphs -- the stage attached by the parasitoid E. hayati. (Above) Adult silverleaf whitefly.
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