BT for Hornworms

[kwselke]

I've spent the last two days trying to find the hornword that is chewing up the leaves on one of my plants and leaving nasty looking droppings all over it. This morning I decided to go biological on it and bought DiPel brand BT powder. I came home and dusted the plant and hollered 'Come and Get It'. Now an hour later it's raining. Should I redust after each rain or will the BT in the powder stick to the plant as a liquid form of BT would.

[Suze]

It depends on how much it rains. If just a light rain, probably no need to reapply. If you get a good downpour for several hours, probably so.

[kwselke]

Thanks. My rain gauge indicates I got 0.80 inch in about an hours time. I guess I'll reapply. The way it's been raining down here I'll probably have to apply twice a day through the weekend.

[Suze]

Originally Posted by kwselke

Thanks. My rain gauge indicates I got 0.80 inch in about an hours time. I guess I'll reapply. The way it's been raining down here I'll probably have to apply twice a day through the weekend.

Well, I don't know if you'd want to do all that. :wink:

Maybe reapply twice a week until rains stop.

Since your plants are already wet anyway, one thing you can try is to hit the plant(s) with a vigorous spray from the water hose. Sometimes they will wiggle and then are much easier to see.

Looking for them at night with a blacklight might be another option.

[kwselke]

Suze,

Thanks again. The rains have subsided for the time being and I went back out to poke around the affected plant and do another light dusting. The plant in question is an Early Girly in a 15 gallon container and is loaded with ripening fruit. After I put the BT away I took another look at the plant and there was a two inch hornworm squigling on the top of my potting mix. It got squished. It was small, so I have a hard time believing it was the only one doing the damage to the plant. There is a 50% chance of rain again tomorrow. I'll wait a few days and confirm additional damage before applying BT again.

[Suze]

kwselke, I just thought I'd mention that I do preventative treatments for caterpillars in general and rarely see any hornworms, cornworms, leaf rollers, inch worms, etc. later on in the season. When the live oaks start to "bloom" and start dropping leaves, I throughly spray my tomato plants and also all my emerging cannas with Bt.

Then I repeat a couple of weeks later. That's it. This seems to prevent the population from getting a foothold.