bacillus thuringiensis shelf life

[Chris Conlan]

Dan,
        Contrary to an earlier response to your post this stuff does not
last forever and it doesn't kill everything.  The shelf life also depends
on the type of formulation and how it is stored.  Powder and granule
formulations tend to last longer than liquids.  I'm going to assume your
stuff is a liquid.  If it was stored under cool conditions or near room
temp it will probably be OK for at least one year and maybe even 2 years.
If you are like most people and it was left in a hot garage or storage shed
for the summer it may not have much left in it.  It's usually best to get a
fresh batch every year.  Once you dilute it into water it probably won't
last long.  Keeping it dark and cool will help lengthen the shelf life.
Sunlight is murder on the stuff and once applied the sun usually causes
most of it to break down within a few days.
        B.t.'s also come in a variety of strains and while it may be that
your sample is old and weak it also may just not be a particularly active
strain for Squash Vine Borer.  I honestly don't remember whether the
kurstaki strain is good for vine borers (it probably is but it's been
awhile!).  You also may just be experiencing a delivery problem.  Since the
vine borers are inside the stems and the B.t. must be consumed to be
activated you just might not be getting the toxin to your subjects in a
high enough dose to work (even if injected).  Also, B.t.'s tend to work
much better on the early instars.  I hope this helps a little.  Let me know
if you have any other questions and I'll do what I can to answer.

Chris
conlan at adnc.com