It is not a matter of a few leaves, when you see a complete nursery denuded of all leaves you will do 1 of 2 things, nothing and live with it, spray/dust with whatever works.  Are there long term residual problems with dusts or sprays, I don't know, we ate tomatoes my whole life that had been dusted with Sevin and other than a mysterious addition to fig trees there does not appear to be any effects, effects,effects, effects, LOL

Wow, didn't realize you had such a big problem.  
I was just trying to point out that you need to be careful with the pre harvest interval (PHI) when using stuff like Sevin. 
Sounds like this is not a factor since these are nursery trees.

In case you have time and want to try some alternative approaches to get rid of grasshoppers and crickets here is a link;
https://www.greenharvest.com.au/PestControlOrganic/Information/GrasshopperControl.html


 Good luck with it!