I applied neem oil with a few drops of castile soap to a WW plant (showing thrip damage) in a 5G container and mixed per the label directions. I applied around dusk, then the next afternoon it rained hard around 3" worth in my rain gauge. The spray was on the plant around 18 hours before the rain.
Is neem oil a systemic that gets into the plant tissue for longer lasting protection, or do I need to go ahead and plan a re-application?
The leaves still have a bit of “sheen”, so I think the neem oil may still be hanging in there - but not sure if its still effective?
I would reapply periodically until they are gone. If that doesn’t work for you there are other natural methods to combat them.
The recipe I’ve used is 1 TBSP Neem oil and 1 TBSP Bonner’s per quart water. If needed you could increase the Neem say up to 2 TBSP in above recipe.
Not my recipe but from others