Losing chlorpyrifos from our toolbox has created a noticeable gap in how we manage Argentine StemWeevil (ASW) during pasture renewal. Previously, applying chlorpyrifos at spray-out helped tidy up resident ASW populations before new seedlings emerged. While we still have some control options available at spray-out, none are as reliable. We also do not have post-emergent options on label that deliver anything close to the level of ASW suppression chlorpyrifos gave us during early establishment.
Options include seed treatments, but under high pressure, decreasing the risk prior to drilling is best. So, cultural practices matter more than ever. To establish new pastures, especially during the vulnerable early window before endophyte expression kicks in, we must stack the deck in our favour. One of the most effective cultural tools we have is also one of the simplest, albeit often an unpalatable one: spraying out early, ideally six weeks before drilling.
Bringing it all together
Pasture renewal is an important on farm investment and worthwhile getting right the first time. Without chlorpyrifos, we no longer have a chemical safety net to rely on.
We still have options to reduce risk, and good cultural practice is more important than ever. Of these, the six-week spray-out stands out as a practical, high-impact step dramatically reducing the risk of early ASW damage.
BENEFITS OF A SIX-WEEK SPRAY-OUT WINDOW
- Starves ASW before new seedlings appear: Early spray-outs removes exisiting food sources, creating a host-free period. Fewer ASW at establishment means less feeding at precisely the stage seedlings are most susceptible. You cannot achieve this decline with a shorter spray off period.
- Limits adult reinvasions: Surviving adults are highly attracted to freshly emerged ryegrass. Any paddock, brown and unpalatable for several weeks, is far less likely to harbour lingering ASW waiting to move into brand new seedlings.
- Protects the critical early growth phase: ASW feeding on cotyledons and early leaves severely stunts or kills seedlings. Early spring temperatures can worsen these issues when growth stages slow during vulnerable stages. Reducing ASW pressure in the early stages determines whether a new pasture 'gets away' or fails.
- Buys essential time for endophyte protection development: Endophytes protect against ASW, but only once they reach biologically active levels inside the plant, typically around six weeks after germination. We align our biological process management with early spray-outs. Seedlings have less risk at the start, and the endophyte gets time to kick in before ASW pressure builds.
- Improves seedbed quality and plant resilience: Longer spray off intervals allow residue to break down, soil to warm, and microbial activity to stabilise. This creates better soil tilth, more uniform seed placement, and stronger, faster establishment. Stronger seedlings tolerate incidental ASW feeding far better than stressed ones.
- Reduces reliance on fragile or inconsistent chemical solutions: While there are some remaining insecticides available for spray-out, they offer nowhere near the security chlorpyrifos once provided. Without good post-emergent solutions available, our best defence is preventing ASW pressure before it begins.
