Tomato Hornworms

Asked September 9, 2019, 1:13 PM EDT

I'm a novice gardener, basically just want to grow some nice tomatoes. What is the best way to prevent tomato hornworms? Also, what causes the bottom of my tomatoes to get black? Thanks, Paulette Wayne

St. Clair County Michigan

4 Responses

Hello Paulette!

Tomato hornworms are the larval stage of a moth that lays its eggs directly on the plant leaf. The only way to "prevent" them would be to cover the tomato plants with some type of netting so that the moths couldn't reach the leaves, but that would make caring for the plants cumbersome. The recommended treatment is simply scouting. Monitor the plants every few days and remove any hornworms that you find. They can be difficult to see--I often first notice the droppings and then look in the vicinity for the caterpillar. Note that the insect has two generations each growing season in our environment. For more information on tomato hornworms, and some additional suggestions on combating them, please see the link below:

Black bottoms on your tomatoes sounds like blossom end rot. Please take a look at the photos in the article at the link below and see if this resembles what you’re seeing on your fruit. (It starts out as a much smaller area than shown in the illustration.) Blossom end rot is caused by a calcium deficiency in the plant. This can be due to a lack of calcium in the soil, but is more often due to uneven access to the water which transports the calcium. The article describes several ways that you can minimize this condition.

If you would like confirm that your soil has sufficient calcium, you can order an MSU Soil Test Kit here: The report created includes an analysis of your soil and recommendations for what you are planning to grow.


Thank you very much for the information. I apologize for not getting back to you sooner. I now have a better understanding of the problems and will spend the winter coming up with a new plan.

Paulette Wayne

Hi Paulette!

You're welcome!

I don't remember if the articles mentioned that the tomato hornworms are not necessarily an every year occurrence. Several years ago, I pulled 7 or 8 of them from my plants. The next few years, there were none. I saw a little bit of damage last year, but never found the larvae. This damage at all. Don't be discouraged.

Blossom end rot can be managed with regular irrigation. How difficult that might be obviously depends on how convenient your water source is. If you have an outdoor spigot nearby, you might try running a soaker hose thru the tomato bed. When you need to water, you can simply attach the end of the soaker hose o a regular hose and run the water. (I'd set a can get pretty soggy if you forget it's running!)

Good luck with your gardening!

Thank you so much for the additional information! I was using containers on my front porch in the past and I think that is part of the problem - drainage wasn't good and I had trouble keeping them from being under/overhydrated. They are going in the ground next year and I am considering the possibility of making small greenhouses to keep the hornworms out. I live in the country and have a feeling they might live here, too!

I am keeping all of your information! I really appreciate your enthusiasm and encouragement! Paulette