Wednesday, July 7, 2010

Attack of the Killer Hornworm

This year I have been struggling a little bit with growing Tomatoes. In case you didn't know, I grow mine in large containers. The heat that came upon us so quickly really didn't help matters much. I continue on though. I have made some Spaghetti sauce and have had a decent amount of Tomato and Jalapeno sandwiches. Hey, don't knock them, they are great with Miracle Whip and black pepper!!
I water my plants almost everyday, talk to them every time I go by, just hoping that they will produce more tasty treats. Then.....THEY CAME!! The Manduca sexta, better known as the Tobacco Hornworm. Here is the latest Post Office photo:

I know what some of you are saying, that looks like a Tomato Hornworm. Those guys are known as Manduca quinquemaculata. They look like this:

The Tobacco Hornworm larva (Manduca sexta) is generally green with seven diagonal white lines on the sides and a curved red horn. The Tomato Hornworms (Manduca quinquemaculata) have eight V-shaped marks on each side and their horn is straighter and blue-black in color. Either way, they are both known as nasty little, Tomato plant eating varmints! They both also eat, Peppers, Eggplants, Potatoes as well as Tobacco.
These "Hornworms" are the larvae of the hawk or sphinx moths, also known as Hummingbird moths.

The Hawk moths (Tomato Hornworm moths)are large, heavy-bodied with narrow front wings. The moth is a mottled gray-brown color with yellow spots on the sides of the abdomen and a wing spread of 4 to 5 inches. The hindwings have alternating light and dark bands. They are usually seen after dusk. The moth doesn't cause any damage.
The Sphinx moth (Tobacco Hornworm moth) are usually much more colorful.

There is conflicting information about the origin of these two "horned" pests. One report has it that ships bringing tobacco plants (and the Tobacco Hornworm) from Nicaragua to Virginia in 1641 introduced the insect. Then there are reports that the Tomato and the Tobacco Hornworm are native to the United States.
Either way, the larvae (hornworm) is the damaging stage and feeds initially on the upper portions of leaves, giving you stripped stems and leaving behind dark green or black droppings. If you see something that looks like this on your Tomato plants, look around, you have a visitor.

The larvae blend in with the plant canopy, and therefore go unnoticed until most of the damage is done. They can bend and curl to look just like a leaf. The poop is usually the best way to locate them, it drops down, so look up from it.
The best advice is to examine plants frequently from early July through the rest of the growing season for hornworm eggs and small caterpillars, and to begin control measures as soon as young larvae are observed.

To control these little beasts, handpicking is recommended. I like to take them off the plant, put them on the concrete or out in the road and watch the birds come get them. You can also cut them in half with your garden shears. If you are a little squeamish or just can't get yourself to pick them off, BT (Bacillus thuringensis) can be used. It is very effective, especially on smaller larvae.
Of course, there is one time that I don't mind seeing a hornworm. I know, "What are you crazy?!" Probably, but that is besides the point. No, I enjoy seeing them when they look like this:

All those white, rice looking things are cocoons. They are from a small braconid wasp, Cotesia congregatus. Larvae that hatch from the wasp eggs that are laid on the hornworm feed on the inside of the hornworm until the wasp is ready to pupate. The cocoons appear as white projections protruding from the hornworms body. If you see a hornworm like this, leave it alone. The wasps will kill the hornworm when they emerge from the cocoons and then will seek out other hornworms to inflict the same fate. Mother Nature can sure be cruel sometimes.
Hopefully, this pest will not be a nuisance to you, in the meantime......I must go feed some birds!
Happy Growing!


  1. They also leave pupa in the soil. I recently emptied my earthboxes to prepare for a fall crop & found several of these in the soil. Really big, weird looking thins.

  2. Brenda, Texarkana, TXJune 26, 2011 at 3:37 PM

    Yes, they are strange beasts! I found one today on one of our tomato plants, which we also grow in big pots. The thing DID NOT want to let go of the vine. The poop they leave behind is huge, so before you eat those tomatoes, be sure and wash, wash, wash!!! Or should we not eat them at all (the tomatoes)?

  3. Hey Brenda, there is no harm in eating the Tomatoes. Washing is a good thing, but the poop is no cause for alarm. To me the poop is a great way to find the little suckers. they are sometimes hard to see.

  4. All of you are really mean and Darren, you are just downright sadistic. I'm sure there is a special place for you. Why kill something that is not bothering you. All you need to do is place the caterpillars on one host plant. What stupid people.....

  5. Anonymous, I thought long and hard about deleting your comment, but, everybody does have freedom of speech. Then it dawned on me, what a GREAT teachable moment.
    You said: "All you need to do is place the caterpillars on one host plant". That would be fine and dandy, however, a couple of these creatures can devour an entire plant. What then? They move on to another. Do I then leave them on that one? They devour that one and move on, where does it end?
    You also said: "Why kill something that is not bothering you". I am assuming that you leave termites alone then when they are eating the wood in your house? They are not bothering you.
    What happens if an army of ants invade your sugar bowl? Do you leave them alone? They are not bothering you.
    I use these tomato plants as food for my family. I am assuming that the sugar and the house is used for your family.
    As for me being sadistic, I am only helping another creature to find what they would normally eat on their own. I am making it easier for birds, How is THAT being sadistic? Am I not helping another creature to survive?
    What ever happened to survival of the fittest?
    There is a lot of work that goes into a garden, you may or may not be a gardener, I don't know, but trust me there is a lot of work involved. To have it all eaten by some little worm is very disheartening and does not help to feed my family.
    Do you eat meat? I do. Does that make all meat eaters sadistic? Maybe.
    If you want to get right down to it, eating lettuce can be considered sadistic, it's alive also. Is it not?!
    Please make sure you know all the facts and views before calling anybody stupid or sadistic. I probably will never hear from you again, but if you so desire, I would love to have an actual conversation and discuss this topic more, preferably without any name calling.

  6. Wow. I just removed two of the hornworms with the wasp larve on them. I did not kill them, I simply broke off the small stem they were on and took them 500 feet away to the woods. My tomatoes are still flourishing and I havent seen another hornworm in weeks. This was a really cool article. Thanks!

  7. Darren, the other anonymous person (not myself as i love meat and couldnt live without it as well and think vegatarianist lifestyle is redundant and i didnt climb to the top of the food chain to eat carrots, picked some of these lil green bastards off of my pepper plants and threw them against a wall but kept two in a jar to watch grow and metamorphasize) is just what i call a "fat vagina" reguardless if someone is sadistic, you dont spend days creating a garden in the 115 degree Arizonian weather to have these pests ruin your yeilds of peppers for Quesadillas just out of the 'kindness of your heart' you burn their heads off, squish em with much thorough pleasure, throw them, feed them to your tarantula and then get on with your live and get on gardening. Other anonymous, you sir/ma'am are a giant pussy if you cant come to extirminate something that acts purely on instict and doesnt even have the caapacity to realize its even alive.

  8. Please, I saw this worm in the cotton crop, anyone knews what was. This Manduca sexta, better known as the Tobacco Hornworm can be attacks cotton???? Thanks Luanna Barreto (agronomist from Brazil)

  9. Luanna, From the research I have seen, Tobacco Hornworms do not attack cotton. However there is a caterpillar that closely resembles the Hornworm that attacks is the Tomato Fruitworm. You can see a picture here:
    Hope that helps.

    1. Hello there sir. I noticed some of the tomato hornworm left some hibernating caterpillars in the soil when i was moving soil to relocate my raised beds. The thing is i picked about 6 of them so far. Now i was planning to plant some kumquat trees in my raised beds. And i was wondering if these green tomato horn caterpillars will eat my kumquat plants? I am afraid that i missed some since there is a lot of soil. now i just have kumquats and a lot of dwarf citrus in my raised beds now where my tomatoes were. Do you think these green caterpillars will eat all my citrus if they come back out when its warmer out? i also planted some pomegranate plants. i hope they wont eat my pomegrante plants either?!?!? let me know!!!

    2. Hello Aaron,
      Good question!
      The answer is No. The Tomato Hornworms will not eat your Citrus trees. They prefer Tomato, Tobacco, Peppers and such...Citrus is not on their menu.
      Pomegranates either.
      They should be just fine.
      Hope that makes you feel better.
      Happy Growing!

  10. I'm in upstate SC in zone 8. (I moved here from Charleston actually -- couldn't handle those brutal 130 degree heat index days.)

    I grew tomatoes and Basil in an Earthbox and saw a few of those fat green worms with black markings midway through the season. I wish I'd read your article then.

    My tomato plants stopped producing and the lush basil turned light green with streaks of white running through the stems. Luckily I got about a dozen nice tomatoes and some bunches of basil before they got sick.

    Of course I didn't know what to do. Except for trimming, did nothing. Then when it was obvious they'd had it, I dug both up and hopefully got most of the roots. I have a pear tree on the other side of the yard that had fire blight. I thought that might have compromised these plants too. I didn't throw out the soil though. It is probably loaded with the hornworm excrement. I planted some Rosemary and Thyme there. Will they survive or should I throw out the soil and herbs and start over?

    I wanted to keep everything organic.

    1. Anonymous,
      You did not mention when your Tomatoes and Basil went South.
      Was it early in the season, late in the season or about midway through.
      Were you keeping a good eye on the soil moisture?
      If it was fluctuating wildly or allowed to dry out too much, that could have been the problem. Especially in a box.
      The fire blight should not be a problem for the tomatoes or the basil. There should also be no problem with the soil for your Rosemary and Thyme.
      IF, you have the same problem again this year, then I would suggest disposing the soil and starting from scratch, you may have picked something up from your compost or whatever it is you use.
      Hope that helps.
      If you have any other questions, shoot them to my e-mail box....

    2. Thanks I'll do that. In answer to when I started to lose the tomatoes and Basil, it was actually maybe in September.It was still very nice warm weather. I still had a bunch of partially grown green tomatoes that stopped growing. It was strange because everything seemed healthy early on and then all of a sudden that changed. Regarding the watering, for me it was pretty consistent which isn't saying much. But the Earthbox has that self watering mechanism which helped. There probably were times when they were over-watered as well as under-watered as they got water every time it rained (as I didn't bother to use the plastic cover the boxes came with to cover the soil) besides when I watered them (with captured rainwater from the roof that I stored in barrels).

  11. Would like to reproduce your tomato hornworm larva and adult pics in my training manual. Can you contact me so we can discuss? Thanks!

  12. Hey Darren,
    This is an awesome article. It's really refreshing to read someone who actually understands what they're writing! :-) Couple things ... the egg and newly hatched hornworm image from above does not show up in my browser and I get a page can't be found if I try and copy the link into another tab. Any way you can replace / update?
    Also, I'm not a gardener; I just built the above ground box for my wife and daughter to go plant a bunch of stuff in. Now I'm being consulted as entomologist and Chief Worm Picker :-) I'm in warm and wet Miami. They planted the tomatoes (amongst other things) in October. (The soil was purchased from a local nursery.) Now we're got a sizable population of worms that require daily "harvesting" - love the idea about the driveway (can't imagine why anonymous would object to feeding birds; take it up with them if you have a problem!). My question is: are the new worms that I'm finding coming from previously laid eggs (by the moths) that would be on the underside of the leaves? I'd like to get "ahead" of the problem just a bit if I can. Thanks, Paul

  13. So glad I found this.....Found 3 this morning. 2 on my tomato plants and 1 on my salsa pepper plant. Grabbed one by accident which is how i found it...(made me jump and caught me by surprise) . We thought maybe grasshoppers were devouring our tomato plants but only found a few. Then I thought Rollie Pollies (trashed the tomato's last year) but found barely any this year...but now I know....SO I clipped their lunch (the leaves they were firmly attached to) off the plants and sent them on a flight into the empty plot behind the house for birds or whatever to enjoy. Now I know what to look for in the soil and on the leaves. :)

  14. Thanks for the information you shared on this. I found the hornworms (two had the wasp larvae all over them) after wondering what in the world could denude a tomato plant seemingly overnight. Happy gardening to you!