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How to control Tomato Hornworms

Tomato Hornworm control

(Manduca quinquemaculata)


Tomato Hornworms cause serious damage:

Tomato Hornworms are the blight of tomato growers everywhere. They can quickly defoliate tomato plants and ruin your crop.  Therefore Tomato Hornworm control is key to tomato growing success.


Tomato Hornworm’s are tough to find:

  • However, for the home grower Tomato Hornworm’s are fairly easy to deal with if you can detect them; just pluck them off and dispose of the pests.
  • But that’s the problem, Tomato Hornworm’s, are exquisitely camouflaged and rather difficult to detect.  This is especially true of the small-young ones.
Tomato Hornworm control

Tomato Hornworms can be hard to find, even if you know where they should be hiding


Traditional ways to find Tomato Hornworm’s:

  • However, there are some clues you can use to detect their whereabouts.
  • For example, looking for them where you see a bunch of munched leaves may help to get you in the ballpark of where they are hiding.
  • In addition, a cluster of green-black pellets (the poo) might be found just underneath a larger Hornworm.
  • Despite these clues, I still find it difficult to find these tomato killers in normal daylight.
Tomato Hornworm: close up

Tomato Hornworm: close up

Tomato Hornworm glowing under UV light

Tomato Hornworm glowing under UV light… like a 1970 rock poster!


Awesome tool to find Tomato Hornworm’s:

  • Fortunately, I recently discovered a very easy way to find the stealthy critters.  Tomato Hornworm’s glow brightly when you shine a black light or Ultra Violet (UV) light on them.  With this light as your new weapon, they don’t stand a chance.
  • The best time to go hunting is at dark when UV light enhanced Tomato Hornworm’s glow bright blue against the background of night.  It’s actually kind-of amazing how they pop out.

Other uses for a UV flashlight:

  • The UV flashlights will also help you find scorpions-if you are looking for them.  This is actually why I got these flashlights to begin with.  Actually, I got two UV flashlights after we found a scorpion that was too close for comfort.  I wanted to make sure that there were not other scorpions hiding in the corners.  Scorpions will also glow bright under the UV light.. also hard to miss them with this tool.
  • Many people also use UV flashlights to find pee (or other body fluid) stains on things.  Not a bad idea if you are staying in some unfamiliar places such as hotels.  Lots of pet owners also use the UV flashlights to track down the naughty smells of their pets.  A UV light may also help you find mice/rat hangouts because those rodents pee where they eat and hide.
  • There are all kinds of other things you can do with a UV light ranging from authenticate oil paintings, antiques and banknotes.  Many more uses for a UV light via wikipedia.  http://en.wikipedia.org/wiki/Black_light


How to get a UV flashlight:

  • You can get these UV flash lights at many places.  I found mine on Amazon.com, but I am sure you could also find them at your favorite psychedelic store.
  • If you really want to optimize your shopping, there are two important variables to keep in mind when you are buying one of these flashlights.  The shorter the wavelength and the higher the wattage the better, (but also more expensive).
    • 1). Higher the wattage = brighter the light.
    • 2). Shorter wavelength = more of the UV glowing effect you will get- a lower nanometer (Nm) number is better.


    I bought two UV flashlights for myself on Amazon.  One is 395 Nm flashlight and the other is a 385 Nm flashlight.  They both work very similar, but you get a tad more glow with the lower wavelength number.  However, the last I checked on Amazon, the 385 Nm flashlight that I got is out of stock.  I now also see that there is a 365 Nm flashlight on Amazon which is more expensive, but should really turn on the glow effect (see last link below).  This really low UV wavelength light (365 NM) might be overkill, but I just might get it anyhow for the dramatic effect.

395 Nm Ultra Violet Flashlight

385 Nm Ultra Violet Flashlight

365 Nm Ultra Violet Flashlight


  • There are more expensive UV lights around if you are doing professional forensic work or professional inspection work.  However, I don’t think it is necessary to throw out that much cash.  For our purposes, anyone of the lights that I have linked to above should be just fine.


I added additional amazon picture links below to 3 excellent customer rated UV flashlights.  However, for some reason the picture links don’t show up on all web browsers.   Therefore, for those using browsers that don’t allow the pictures to show up,  I am also adding regular hypertext links below to the same UV flashlights.

400 Nm Ultraviolet Blacklight Flashlight 3 AAA

395 Nm Ultraviolet Blacklight Flashlight 3 AA

365 Nm Ultraviolet Blacklight Flashlight 3 AAA

About Thomas Osborne, MD

Dr. Osborne is a Harvard trained Radiologist and Neuroradiologist who loves to share his insight about medicine and gardening.


  1. Great info, Tom. Did you know that the Hummingbird Moth, a beautiful and very large moth, is the adult Tomato Worm? If you spot these moths in the Spring, beware. They are busy laying eggs on your tomato plants!

    • Thomas Osborne, MD

      Hey Stasi. Thanks for bringing up that additional information. I knew the Tomato Hornworm was the youth of the Hummingbird moth, but I have not seen one yet.

  2. I just want to claim credit for the discovery of the tomato hornworm blacklight fluorescence. I discovered it years ago when I was a medical student in Davis, California, and found tomato hornworms in my plants. I used a fluorescent desk lamp, a blacklight bulb, and a long extension cord, on the off chance that I could find them better after dark, and it worked! I had a letter printed about it in the Mother Earth News, but the concept has been slow to reach the world at large. I posted it in the Wikipedia article about tomato hornworms, but someone deleted it, saying that they could find no pictures or references on line about this. I put it back, not sure it is still there.
    Good Hunting, Richard Buss, M.D., Jackson, California

    • Thomas Osborne, MD

      Hey Richard (AKA Country Doc)

      Thanks for the note and congrats on your early discovery.
      You are welcome to use my hornworm pictures for your Wikipedia article.
      I only ask that you reference my images appropriately.


      • Hi Richard, In the last couple of days we’ve spent hours in search of these creatures. We found the information about the blacklight in Wikipedia and are in search of a UV flashlight. We are spraying BT, which pretty much only works on the smaller hornworms. It’s best to start spraying in the spring, so the newly hatched caterpillars munch on the leaves and die from the BT. It is necessary to repeat spray until no more eggs are being laid.
        We looking forward to the hunting expedition in the dark!

        Thanks for your work.

        Margo Sorokin

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