you sound sure. have you tried this on them. i would think that the location of the stem todes inside the plant might protect them from a benny todes application. i have no experience with benny todes for combatting stem todes it was just a thought. ive used them on thrips and i got rid of them but it was part of an ipm including spinosad. im not sure which thing killed em but they are gone
thrips are a cake walk with organic spinosad judging from reports of just using that by members, i also used benny todes just to be thorough..
I have no experience fighting duds or stem nematodes but I know the bennies can and are recommended to be used as a foliar... during the night/lights out hours... they might seek out the harmful ones?
organic ACT might help too, its loaded with beneficial bacteria and fungus. Using nature vs nature might be the best way if none of the chemical stuff is killing them... and chemical stuff just makes for stronger breeds of bugs anyway... but I should just shut my mouth and learn what works