Something is Eating My Tomato Plants!

Something is Eating My Tomato Plants!

entomoligists

You walk into the garden and suddenly notice that part of your tomato plant has disappeared. Where there were leaves yesterday, only bare stems remain. The damage is too high for it to be a rabbit… “What is eating my tomato’s leaves?” you wonder.

Chances are, it’s the tomato horn worm. These are the larva of Manduca quinquemaculata, which hatch out from the eggs laid by “sphinx”, “hawk”, or “hummingbird” moths. They are large, green, and hard to see, but they take big bites and can quickly strip a big section of your tomato, pepper, eggplant or nicotiana plants. In fact, they eat other members of the Solanaceae family, and because many of these plants have toxic substances in their foliage the larvae get protected by those toxins. 

Here’s what you need to know about tomato horn worms:

1. They are large, but nevertheless, they are hard to spot. Look on the stems and edges of partially eaten leaves just under where you see bare stems and branches.

2. Because they are so fat it’s hard to bring yourself to squash them. I put them on the bird feeder for the crows to feast on. If you don’t have an active bird feeder, and can’t bring yourself to smash them, bring them into the store for Rachel. She feeds them to her bearded dragon lizard.

3. If you’re unsure if the damage you see on a plant is done by horn worms or animals, look for the horn worm frass pellets. Frass is what entomologists call larvae poop, and the bigger the larvae, the larger the frass pellets.

4. If you find a tomato horn worm that is covered by what looks like grains of white rice, leave it alone in the garden. These are the pupae of  the Braconid Wasp (Cotesia congregatus) a parasite that actually eats the hornworm alive. (We humans think nature is lovely, but it’s a wasp-eat-worm world out there.) These tiny wasps are no danger to humans but they help keep the hornworm population down.

5. Early in the hornworm’s life spinosad would be an effective treatment but usually there aren’t that many of them. Handpicking is probably faster than bringing out the Captain Jack’s in this situation.

6. If you find a hornworm be sure to show it to any kids in the area.

This is the hornworm (on the ground) that I found recently on one of my pepper plants. Notice the frass pellets that dropped at the base of one of the leaves.

This is the hornworm (almost upside down on a stem on the ground) that I found recently on one of my pepper plants. Notice the frass pellets that dropped at the base of one of the leaves.

tomato_hornworm_parasites

These are the pupae of the Braconid Wasp on a Hornworm. The tiny female wasp lands on the worm and slides eggs into the worm. They hatch into larvae and literally eat the worm from the inside. When they are done feasting, they pop through the worm and pupate on the back of the dying hornworm, finally hatching out into more wasps again. It’s a tale right out of a horror movie, right?

tomato_hornworm_pepper

Here is my row of peppers – the damage was so extreme on the end plant that I though rabbits had eaten it. Can you spot the hornworm?

8 Comments

  1. Stacey on July 28, 2016 at 7:17 am

    I planted a cone flower and several marigolds, within 10 days time, something ate my marigolds to the stump and my coneflower all the petals have nearly vanished. What kind of critters would have done this.
    Thank you,
    Not a happy camper-Stacey

    • CLFornari on July 28, 2016 at 7:33 am

      Stacey – that sounds like either slugs or earwigs on the marigolds. I’ve learned to dust newly planted marigolds with diatomaceous earth as soon as I plant them – usually only one dusting over plants and soil around them is enough. Once they get growing and are garden-strong, the slugs and earwigs don’t find them so appealing. The coneflower petals were most likely eaten by either earwigs, or more probably at this time of year beetles. Japanese beetles and Asiatic garden beetles love coneflower petals. Again, DE can be a plant-saver here. Yes, it looks like it snowed baby powder when you first put it down, but that washes away over a week or so and then the problem insect has moved on or died.

  2. Betty Myska on July 28, 2016 at 7:17 am

    Very informative article. My nine year old granddaughter was fascinated by this worm. I had three on one plant. I removed them and then saw the rice like stuff but didn’t know what that was.

    • CLFornari on July 28, 2016 at 7:34 am

      Yes, Betty – kids love these critters! In future leave the ones with the rice-like pupae and that will help control future populations. Glad your granddaughter has her eyes and mind open in the natural world!

  3. bob fraser on July 28, 2016 at 8:37 am

    could also be a woodchuck. have seen one eat new purple cone flowers before. but it does eat the whole flower not very selective.

  4. KVetrano on July 31, 2016 at 7:16 pm

    Hi, My basil was absolutely decimated, we even planted it in pots, thinking it would be safe from asiatic garden beetles. I’m planning on getting more plants, but thoughts on how to protect them this time?

    Thanks!

    • CLFornari on August 18, 2016 at 9:27 am

      You could cover basil with floating row cover, especially at night, if the garden beetles are to blame. Be sure it’s not earwigs, however – they also eat at night and love basil. For earwigs dusting with DE one time usually does the trick. An organic solution!

  5. Diane Ranney on August 7, 2016 at 10:20 pm

    Hornworms are so gross,but my brother-in-law has been keeping them in check and off his (over 35) tomato plants (in Maine). He scans the leaves every day and checks for the tiny pearlescent eggs and crushes them between his fingernails. They are so less icky at that size! So far, he’s managed to keep them at bay. Last year, with about 25 plants, he harvested over 200 lbs of tomatoes of several varieties and never used chemicals of any kind. Definitely my role model for gardening!

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