Our tomato plants seemed to be doing so well and then suddenly started looking bad. It’s true that the weather has started to change but there are still a lot of green tomatoes.
We are practicing organic gardening, so bugs are to be expected but up until this point, we had not seen any.
Suddenly, I noticed a few bugs that I had not seen before and a few of the tomatoes, that were just starting to turn red, were going bad on the vine. I was finding round spots of mold that I suspected had started out as small bug bite marks.
Yesterday morning I went out to check on the balcony garden as I do every morning and I found this disturbing beasty…
The next day, I found this gigantic caterpillar!
I did some research and found that these are Tomato Hornworms. It’s amazing that they could show up on a 3rd floor balcony, so our first question was, how did it get there? Did they hatch there or climb there?
The next couple questions we had were: what will they do to our plants and what should we do about them?
We don’t mind sharing with a few little critters but we also, dont want them to demolish our plants. Time to do some research! This is what I found out:
With some research I found that Hornworm eggs are deposited on the plants by Hawk moths in the spring (also called, Sphinx moths and hummingbird moths). Hawkmoths are described as olive green in color and resembling hummingbirds.
The Hawk moths locate the tomato plants by scent. The moth eggs can take less than 1 week to hatch. The hatchlings are small and hard to spot. They hide during the day but can devour whole leaves over night. They will also eat the flowers and tomatoes, as well!
If you don’t want to use any form of spray insecticide, you can hand remove and kill the caterpillars. The problem is they hide very well during the day and feed at night. One article I read said you can hunt the hornworms with a UV black light and they will glow in the dark. We prefer not to use insecticides, so we will probably try the black light. We’ll have to see… I’m not usually afraid of bugs but I am afraid of the dark and giant horned caterpillars in the dark might be a little more adventure than I’m looking for! Lol
Hornworms do overwinter in the soil so if you are using containers, as we are, you may need to get rid of the soil and start with fresh soil in the spring. From what I’ve read, if your tomatoes are planted directly in a garden, you can till the soil after your last fall harvest and again in the spring before planting to kill the majority of overwintering pest.
As for those white “growths” on the top photographed caterpillar… these are the tiny silk cocoons of parasitic Braconid wasps.
A female Braconid wasp injects eggs into a caterpillar’s bodies. The larvae hatch from the eggs and feed on the inside of the caterpillar until they are ready to pupate. At that time, they chew through the caterpillars skin to spin these tiny white cocoons and later emerge as adult wasp.
This process kills the hornworm caterpillar host, therefore, it is suggested that if you see caterpillars covered with cocoons, you leave them alone and allow the wasps to hatch.
Personally, this seems like a drawn out and very painful way to die and I can not help but feel it is cruel to allow the caterpillar to live, just so the parasitic wasps can feed on it but I guess it is not any crueler than killing the healthy caterpillars in order to save your tomato plants. Except, the wasps kill the caterpillar slowly and you will kill the caterpillars quickly.