How long does BT keep?

[Pyrrho]

I bought a bottle of Bt last year to prevent earworm damage on my corn and had good results. I only used a couple of teaspoons to mix with food grade mineral oil, so I've got nearly a full bottle and some of the oil mixture left over. They've been in my garage over the winter (which was mild), and I'd like to know whether either form will have lost its effectiveness. For the cost of a new bottle, I'd hate to find out the hard way, but I don't like the idea of dumping a whole bottle every year.

Any ideas?

[Heritage]

The bottle should be good for a few years if stored cool and out of sunlight. Don't know about the oil mixture - I'd probably dump it.

Steve

[RayR]

I think the short answer—nobody know exactly. My 3 year old bottle of Thuricide liquid still killed caterpillars last year, so don't dump yours.
These BT formulation typically contain both dormant BT spores and the toxic crystalline protein that is produced by Bacillus thuringiensis. The toxic crystals are what stops the caterpillar from feeding and starves them to death even if the live bacteria don't penetrate the gut wall.
The powdered form is supposed to last longer, but who knows.
As long as it is keep cool and away from sunlight, any version should last for some years.

[Pyrrho]

Thanks! I only have a little bit of the oil mixture left, so I'll dump that and start with a fresh batch this year.

[tjg911]

that bottle may out live you depending upon your age!

i wonder if i have the oldest bottle of bt here at tv (?), i bought min in the 1993-1995 time frame. it is still effective, i just used some 4 days ago on cabbage and broccoli plants.

i suggest you store it where the temperature is pretty moderate and constant and out of the sun, avoid hot/cold places like a shed or garage. i keep mine in the basement.

i have very little left in the 16 oz bottle, it may only last a few more years before i use it up and have to buy another. but when i do it will be a smaller bottle as i may not last another 20 years!

tom