Score 1 for jitterbugdude
My plan for managing hornworms while I was away for 9 days was to spray BT (
Bacillus thuringiensis) just prior to my departure, and cross my fingers. Once I returned, I would resume my long practice of manually squishing hornworms and their eggs--a duty requiring walking the tobacco twice each day.
I purchased a 1 quart bottle of ready-to-use (RTU) BT spray. At the same time, just in case that wasn't enough to spray my 130 plants once, I also purchased a 16 ounce bottle of BT concentrate. I sprayed (hand-squeeze spray bottle) all the plants the evening before I left, and the 1 quart of RTU did the job, though empty when I finished.
When I got back, an inspection of the tobacco revealed a scattering of occasional pinholes suggestive of baby hornworm damage, but only a couple of tiny hornworms, and only a few eggs. Wow!
I asked JBD if that is what he typically sees when the BT is working. His answer was, yes. My plan had worked. But then he added that, like the anti-aphid chemical that I use, his use of BT had made tobacco pests a non-issue.
Today, I decided to give it one more spray. To my delight, I discovered that the BT concentrate was exactly 10 times as much BT spores as the RTU. Aha! Easy mixing. Since the spray bottle holds 32 ounces, I simply added 3.2 ounces to the bottle, and filled to 32 ounces with water. That was simpler than the "add x ounces per 5 gallon spray tank" instructions on the label.
I recalled how much my forearms ached after squeezing the pump handle of the hand-held spray bottle from full to empty the last time. One final trial and comparison today.
Hand spraying this morning required about 1/4 the time I usually spend walking the tobacco just once. I was careless with spraying. I'm too rickety to stoop and bend to thoroughly spray upper and lower surfaces of every leaf. The BT spores on the sun-exposed surface will likely breakdown (be deactivated by solar radiation) fairly quickly. But since hornworms don't just eat the bottom surface--they eat all the way through the lamina, and they won't wait for the sun to render the BT non-toxic, well...I expect a decent mortality rate despite my laziness. Time will tell.
The original quart spray bottle, plus the 5 refills afforded by the 16 ounces of concentrate gives me 6 sprayings total for my 130 plants this season. If this does a reasonable job of hornworm (and budworm!) control, then I will have dramatically reduced my tobacco labor for the season.
Thank you to jitterbugdude.
For any chemical haters out there, BT is absolutely safe for everything
except caterpillars of all sorts. It's a bacterium (supplied in spore form), and is rated as "Organic" pest control.
Bob