Entomopathogenic nematodes (EPNs) are increasingly recognised as valuable biocontrol agents for a range of soil-dwelling and, in some cases, above-ground insect pests. For agronomists looking to integrate these beneficial organisms into their pest management strategies, understanding the critical factors influencing their success is paramount. This short post highlights some key considerations to ensure effective EPN application.
1. Selecting the Right Nematode Species:
Not all nematodes are created equal. Different species and even strains within species exhibit varying levels of virulence and host specificity. Consult product information and advisors to identify the most effective nematode species (e.g., Steinernema, Heterorhabditis) for your specific target pest. For instance, Steinernema feltiae has shown control of aphids in propagation and leaf miners, and Steinernema carpocapsae has been widely studied for above-ground pests. Consider that Steinernema spp. generally need at least two individuals to reproduce within an insect host.
2. Strategic Timing of Application:
Optimal timing is crucial for EPN efficacy. Target the most susceptible life stage of the pest. For example, applications against vine weevil larvae should coincide with their presence in the soil. Furthermore, environmental conditions at the time of application significantly impact nematode survival and infectivity. Aim for application when soil temperatures are within the optimal range for the chosen species; for example, Heterorhabditis bacteriophora performed best at 9°C in one trial, while 20-28°C is generally considered optimum for nematode activity in turfgrass. Avoid application during periods of high UV radiation by applying in the late evening or under cloud cover.
3. Effective Application Methods:
EPNs must be applied in water using standard spraying or irrigation equipment. Ensure filters in spray systems are no finer than 0.3 mm and consider removing them to prevent nematode blockage. While some Steinernema species can be applied via Dosatron systems, consider the distance between drippers and the root ball for optimal placement. For turfgrass applications, mowing the grass short and ensuring moist soil prior to and after application is important for nematode penetration. In some cases, modified equipment for soil injection may be necessary to reach pests like leatherjackets and corn rootworm.
4. Managing Environmental Factors:
Maintain adequate soil moisture before, during, and for a period after application to prevent desiccation. Washout of nematodes can be a concern, particularly in rockwool media. Be aware that temperature extremes can negatively affect nematode performance, with efficacy potentially reducing above 30°C. Understanding the temperature tolerance of the specific EPN being used is vital.
5. Considering Formulations and Adjuvants:
EPNs are formulated to aid storage, transport, and application. While some studies suggest spray adjuvants may not significantly impact overall efficacy against above-ground pests in all cases, others indicate their importance for protecting nematodes from desiccation in foliar applications. Select adjuvants carefully, as some can negatively affect nematode survival and infectivity. Gel formulations have shown promise for improving above-ground efficacy.
6. Integrating with Integrated Pest Management (IPM):
EPNs can be a valuable component of an IPM strategy. Consider their compatibility with other biological control agents. For instance, Dalotia coriaria (a predatory mite) appears to be mostly compatible with S. feltiae and H. bacteriophora. In vegetable crops, Purpureocillium lilacinum (a nematophagous fungus) can complement nematode management.
7. The Importance of Knowledge and Education:
Grower understanding of EPN biology and application is crucial for success. Stay informed about best practices and seek guidance from advisors. Ongoing research continues to refine application techniques and expand the range of pests controlled by EPNs.
By carefully considering these factors, agronomists can maximise the potential of entomopathogenic nematodes as a sustainable and effective tool for pest management.
