Yes, combining oil and Bt-k has been done successfully for generations. I strongly recommend that you locate a vegetable based horticultural oil for this purpose, as such a product will have an emulsifier mixed in. The emulsifier will enable the Bt, whether a powder or a liquid form, to be dispersed evenly. I don't have a recipe, but I'm sure that you can find one on-line somewhere.

However, I have never heard of anyone spraying this on. You only need a few drops applied to the very tip of the ear. Time consuming, yes....but very effective. I've always used one of those plastic syringes for the job.

If you wish to use the oil alone, just find a vegetable based oil, such as canola (rape seed) or soybean oil.

As with all pest control measures, timing is everything. Call your local Cornell extension office to find out when the best time of application is in your specific location. As a matter of fact, that's a good place to ask about the amount of Bt you'll need per volume of oil.

How about sharing what you find out, what you decide to do, and how it worked out for you?

Deal. I'm going to try it, because last year, every ear had a worm. I think I'll use an eyedropper, because I have a small corn patch. Johnny's sells an oil for this purpose (together with a gadget to apply it for larger plantings). A few on-line sources suggest applying the equivalent of 5 drops a couple of days after silks appear -- sooner will impede pollination, and later gives the worm time to enter; more oil may leave the ears greasy. You apply it to the tops so that it will make its way down the silks. You apply the solution once; it doesn't have to be reapplied after a rain.

Btk, which stands for Bacillus thuringiensis var. kurstaki, is available from Gardens Alive in the U.S. and NIC in Canada.

I'm interested in this approach because all ingredients are safe for humans, earthworms, and wildlife.

I'll see if I can find out more about proportions and about the exact time to apply the stuff. Meanwhile, advice appreciated from those who have tried it.

NY, look on the third page of this (see attached link) fact sheet from Johnny's. It gives some mixing directions that would apply no matter what you use.

Lots of people have used an eye dropper for this task, and since you have just a few plants, I wouldn't bother trying to find another tool.

Here is a link that might be useful: Check this out

I just harvested the earlier of my two corn varieties, and this seems to have worked out pretty well. 0% worms, compared to 100% last year! The downside is that the upper ends of the ears didn't pollinate well. This could possibly be corrected by adding the oil a few days later and/or using less, but I'm happy with the trade-off.

My recipe: 1 tablespoon DiPel Btk powder to 1/2 cup oil. Mix the powder with enough water to form a smooth, not-too-thick paste. Stir into the oil (which contains an emulsifier) and mix well. Bring out to the garden and apply about 5 drops (1/2 eyedropper full) to corn silks where they enter the ear, keeping the mixture well-stirred. Best time to apply is when the silks have reached their full length and some strands have browned slightly. Only one application is needed; wind or rain won't dislodge the solution. Mix on the day of application and discard leftover solution.

Useful info sheets: application rates, timing and tips.

Store unused powder in the fridge. Open the package at the corner, use a clip to reclose, and place in a sealed gallon zip-lock bag after using. I'd replace it yearly, since it consists of live bacteria.

Thanks to everybody who encouraged trying this out! I'd have given up on sweet corn, it was so wormy.

Another possibility is slipping footies over the ears. I had to do this on a couple of plantings because some birds learned to eat on the ears.

I am not sure of the timing and do not know if pollen will go through the nylon mesh well enough. By timing, I don't know just when the ear worm eggs are laid.