I don't know if I have posted this before but I have had a hell of a time with fungus gnats. Two or three times I thought I had them gone, not talking about one or two gnats flying around but an actual heavy larvae infestation, but each time they came back. The first time that I realized how bad an infestation was in my plants I tried Gnatrol. I noticed on the Gnatrol label that it warned not to use it with anything containing Chlorine (no brainer) or Copper. I could not find any references though, even when I asked Valent, who makes it, as to HOW MUCH copper. The way they word it is kind of wishy washy. I thought they meant if you were using it with like a copper-based fungicide with real high copper content. That was one time I got thought I had them down but didn't. I mention this infestation because that is when I noticed the copper warning.
Now, BTi is BTi, Caps is just as good as Valents Gnatrol. Valent Corp. just happened to pick a certain strain so they could patent it, or maybe because it is easier to culture on a commercial basis, whatever, don't care. BTi is BTi, it's been around since forever.
So, by using Caps Foliar Pack, full strength crown drench (rockwool) and soil drench (moms) applications and making certain that I waited 36 hours after fertilizing and 24 hours after application before using fertilizer again, and have been at this about three or four weeks. I think I have finally gotten rid of them. This is the longest period of time I have gone without seeing any larvae. I know I posted before that I had gotten rid of them but that was before I realized how long the cycle, in heavy infestations, could last. I have calculated a cycle that could possibly go 30 days easy.
Anyway, finally, a friend came upon this from Cornell that mentions Gnatrol should not be used with any compound with levels higher than 100ppm Copper Actually this is a pretty good reference guide as to pest control in general also. I don't know
http://nysipm.cornell.edu/publications/bpguide99/files/biocont.pdf
I know there are other people that have not had it as bad as me and have probably gotten rid of fungus gnats without worrying about the Copper issue, or else they didn't have success with BTi and used something else. This is just a FYI. I am just saying that if you use any kind (hopefully Caps Foliar) of BTi and it knocks them down but they still come back quickly in high numbers, maybe this is why.