In 1986 Michael Gibian completed research on Argentine Stem Weevil (ASW) as part of his BScAgr degree. Since then the ASW life cycle has been observed during insecticide registration work by various people including Jyri Kaapro and Albie Leggett.
In summary we can confirm;
- Over the past 30 years the period over which ASW poses a threat has widened from about 3 months to 6 months as the climate warms.
- Egg laying, which used to commence in early September, now starts in July with larvae found at Avondale GC on 5 August after a bifenthrin application.
- Larvae last for an average 41 days, starting their feeding inside the stem before breaking out then feeding on the root system. The life cycle shortens with increasing temperature so numbers expotentially increase toward late January.
- Larvae do the majority of damage. The presence of adults is only a concern because they will mate and produce more larvae.
- Adults have not been found to fly so their dispersal is by foot.
- Larvae numbers peak on different greens at different times.
Considerations this year;
- History – it is very clear that the ASW is becoming tolerant, if not resistant, to many currently available chemistries. If you have a problem then consider Entemopathogenic Nematodes. Further, Syngenta are also releasing a new ASW larval control product, Spinner®, available mid-September. Spinner® is highly systemic and fast acting with excellent efficacy in trial work. If what you are doing now works then good luck to you but be aware.
- Target – it is most critical given the issues raised above to start control early (August at latest) with adulticides i.e. Bifenthrin (Sentinel), Tempo and chlorpyrifos. Adulticides should be rotated
- Throughout the year – Larvaecide apps should start in September.1
- Programming options:
The threat from ASW is clearly increasing. The program intensity / product mix of your program will depend on the threat ASW currently pose. There are a growing number of golf courses where insecticide control is failing so check larvae and adult numbers regularly, starting now. Don’t be panicked by high adult numbers provided the larvae number is low. Rotate insecticides and look to introduce Spinner® because it is the only quickly systemic option available.