Lots of discussions here about this that the search will pull up if you need more details, but basically the only way Bt works on them is if it is injected into the stems as that is where they eat. Bt has to be eaten to work.

Dave

OK, thanks!

This is what I am trying this year: every evening- inspect for eggs and spot treat them with insecticidal soap. Every other evening-spray base of plants and main vines with Bt until a little run-off occurs, making sure undersides receive treatment. Every week, inject stems every 3 inches with Bt solution, about 1 cc per shot. The soap desiccates the eggs, turning them into hard little discs. I tried manually removing them but they kept falling out of my hand onto the soil which was definitely not where I wanted them to be. I've seen a suggestion to spray the whole vine with the soap but that seemed to burn the tender buds and also I depend on small crawlers like ants (not the fire kind) for much of the pollination and a wider soap spray seemed to reduce their numbers (they came back when I switched to spot treatment only). Adding a drop of spreader sticker helped disperse the Bt spray. I'd also read that sulfur repels the moths and I sprinkled a teaspoon around the base of the stems. Afterwards I didn't find eggs on the tops of the leaf stalks but they were there on the undersides! Too much sulfur can change soil pH so this is not going to be an ongoing solution but I will try laying peeled garlic cloves around the base of the plants, which also have sulfur in them. Whether all this will work is still unknown. I saw my first moth on June 10. I wonder when I will stop finding eggs? They say in my zone we have two generations. I'll keep this up until the plants are either dead or I stop finding eggs, if only to satisfy my own curiosity about its efficacy and whether there is ever a point in the summer in zone 9a when this thing stops trying to reproduce, but I'm not sure I want to devote this much time to one vegetable next year.

squirrelwhispererpup,
I also suggest burying your vines, or mulching your plants heavily so that the main vines are covered up with dirt. That protects the main vine from SVB eggs, and also helps the plant send down more roots. That way you have less vine you have to inspect and inject.

This post was edited by ccabal on Thu, Jun 20, 13 at 12:04

Thanks ccabal. They are in large smart pots and their vines hang over the sides but I think I will see about adding soil to the pots to raise the level and cover at least the bases of the plants.