WINETECH Technical Yearbook 2021

IJs/cm 2 and the control (0 IJs/cm 2 ), but did not differ from that obtained with 20 IJs/ cm 2 (69%). As EPNs are mobile, they can easily move deeper into the soil to infect the larvae, the pupae in their cocoons, as well as the emerging adult. Additionally EPN offer the potential of long-term persistence in the soil. A recent study also showed the high susceptibility of adult weevil against S. yirgalemense and Heterorhabditis indica. Biological control with fungi and in combination with nematodes Three commercial Beauveria bassiana and Metarhizium anisopliae products, as well as one locally-sourced Metarhizium anisopliae , were tested in a laboratory bioassay. Beauveria bassiana products generally performed better than M. anisopliae products, and this difference was statistically significant for pupae and adults, but not larvae. Mortality was assessed after 21 days. Combined treatments were also tested in the laboratory, whereby S. yirgalemense was applied at the same time as the fungi ( B. bassiana and M. anisopliae ), as well as one week and two weeks after fungal applications. In these experiments, both additive (the effect was doubled) and synergistic (the effect was more than

doubled) effects were observed, indicating that mortality could be greatly improved by combining EPNs and EPF in laboratory

experiments (table 1). CONCLUSIONS AND RECOMMENDATIONS

These initial laboratory and small-scale field trials hold promise for moving towards a more integrated approach in managing BFW, which remains the key economic weevil pest in vineyards. These insect pathogens can be applied using conventional spraying equipment, making them a practical solution to controlling BFW. Application is recommended during spring, when temperatures are still cooler and moisture is higher, as hot and dry conditions are not favourable for the efficacy of EPF and EPNs. This is also the time of year when BFW numbers are still relatively low, prior to reaching their peak population numbers. Monitoring is important for correct timing of these insect pathogens, as smaller populations are easier to control than larger ones. Currently effective commercial EPF products are available, with an urgent need to be tested against especially eggs, which are laid on the soil surface. The good results of S. yirgalemense in the control of all stages of the weevil (except for eggs) add to the importance of the success of the mass

FIGURE 4. Feeding damage of weevils on leaves and berries. (Images: Meshack Magagula).

eight species contribute to a lesser extent, probably as their numbers are much less than the BFW (figures 2 and 3). Biological control EPN Biological control using EPN can be targeted against the soil stages of the weevil, which include the larvae, pre-pupae, pupae and the emerging adult, offering a large window of opportunity for the use of nematodes. From laboratory bioassays, there was significant penetration of EPNs on BFW larvae; significant mortality of EPNs on BFW pupae, ranging from 55% to 70%; and significant mortality of BFW

adults, ranging from 24% to 95%. Mortality was assessed over two days. Results from the laboratory trials were used to test effective EPNs in a small- scale field trial, whereby BFW larvae were placed at known locations under the soil in retrievable containers and the soil treated with Steinernema yirgalemense at three EPN concentrations. Soil temperatures ranged from between 8°C minimum to 30°C maximum at the time of applications. Steinernema yirgalemense at 40 IJs/cm 2 (78%) gave significantly greater mortality of the BFW larvae than those treated at 10

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