Looking back through this thread, I saw this: " I am using Bt as a general spray (once a week, depending on weather) to prevent leaf eating critters. "
Bt (bacillus thuringiensis) is live bacteria (once hydrated), which attack various caterpillars and insect larvae, like mosquitos. There are different varieties of Bt, which are specific to different critters:
The most commonly used strain of Bt (kurstaki strain) will kill only leaf- and needle-feeding caterpillars. In the past decade, Bt strains have been developed that control certain types of fly larvae (israelensis strain, or Bti). These are widely used against larvae of mosquitoes, black flies and fungus gnats.
More recently, strains have been developed with activity against some leaf beetles, such as the Colorado potato beetle and elm leaf beetle (san diego strain, tenebrionis strain). Among the various Bt strains, insecticidal activity is specific. That is, Bt strains developed for mosquito larvae do not affect caterpillars
https://www.ext.colostate.edu/pubs/insect/05556.html
therefore you need to know at least generally what kind of critter you are trying to deal with and what strain of Bt you have.
But also: Sunlight degrades Bt after a few hours, so it is best applied late in the day so it can be consumed during the nightly feeding. Keep in mind that your objective is to place the substance where the caterpillars will eat it. In the case of corn earworms, this means squirting the Bt solution into the tips of young ears of corn. Read more:
https://www.motherearthnews.com/organic- ... z3EtuYQudU
So just generally spraying your garden with Bt may not be effective. And it is not recommended, since for the insects that might be affected by it, frequent large scale sprayings are conducive to development of resistance, which insects are very good at:
Although most pest populations remained susceptible, reduced efficacy of Bt crops caused by field-evolved resistance has been reported now for some populations of 5 of 13 major pest species examined, compared with resistant populations of only one pest species in 2005
https://www.nature.com/nbt/journal/v31/n ... .2597.html published 2013.
You are best to spot spray areas where trouble is when you see problems. And remember that you are never trying to eliminate all of any pest, just keep them from becoming major infestation and keep the damage within reasonable limits. You want some individuals to remain, to keep feeding and attracting their beneficial insect predators and to keep a non-resistant population alive, so that even if some individuals develop resistance, the population doesn't.