tomato hornworms and blacklights

margocostasApril 27, 2009

I have heard that you can use a blacklight to find the worms. I found a small bright green catapillar thing while spraying soap on my tomatoes for aphids so I guess I'm getting hornworms now.

Do they glow bright green? I'm not absolutly sure I had a hornworm, but now I wish I would have saved it and blacklight tested it.

My tomatos were getting so bushy I pruned them a little to help with finding pests. I have them planted kind of close, next year I think I will leave more space, this is my first year with my own garden.

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Hornworms are pretty unmistakable. Google "Tomato Hornworm" and search the images of what they look like. The horn on the tail, the markings on the side and the raw size are pretty unmistakable.

Here is a link that might be useful: Here's where I got the image. Don't how good the site is.

    Bookmark   April 27, 2009 at 9:35PM
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Lettuce Loopers are smaller and brighter green than tomato hornworms and might be what you picked off.
While you're searching you might want to take a look at those as well.
I haven't heard of the blacklight trick though, but I imagine at night the white stripes would stand out... When the hornworms come in I'll try it out.

    Bookmark   April 27, 2009 at 9:41PM
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It was a small worm, and green so I immediatly thought of hornworms, baby hornworms.

Yesterday I found a beetle with a big probiscous by my squash plants, I think it's a squash bug. Whatever it is it can't be good.

I'm trying not to use a lot of poisons so I don't kill off my beneficials but I sprinkled some sevin dust at the base of my squash plants and put foil around the bottom too. Someone at work said the glare would confuse the bugs.

I might wander around with my blacklight just to see what pops up. I like to look at wolf spiders with my headlamps.

    Bookmark   April 27, 2009 at 10:42PM
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tom8olvr(Z5 MA)

The glare would confuse the bugs?

    Bookmark   April 28, 2009 at 9:17AM
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That's what I was told, I've read somewhere about the lighter mulch coverings discouraging some pests. I'll try anything. Maybe it will confuse the birds.

I didn't see many aphids or whiteflies around the tomatoes today, I sprayed them with soap water the other day. I got some neem oil to try as well but I also see lady bugs and larva so I'll hold off for now.

    Bookmark   April 28, 2009 at 7:54PM
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austinnhanasmom(5 CO)

Last year I found one hornworm and dusted. I have regretted it ever since. This year, I'm planting borage near and marigolds with the tomatoes. I was also thinking, in the future, I'd "pick" them off the plant and relocate them to a volunteer tomato plant, since the moth is beneficial...

After looking at that photo, I remember how freaked out I get each time I see one. NO WAY could I touch the thing!!

I am crossing my fingers for the success of the companion plantings.

WELL, maybe with thick gloves???

    Bookmark   April 28, 2009 at 8:10PM
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Beneficial? Are you serious? That's like saying mosquitoes are beneficial because the birds eat them! I'm sure your tomato-growing neighbors would thank you if you started encouraging mason bees instead of hornworms!
I'm sorry, I am totally an organic freak, and do everything I can to encourage beneficials in my garden including escorting wasps out of my house to fly away, but there is nothing an adult hornworm could do that would make it beneficial enough for me to encourage their existence. I see one, it dies, period. The best way to get rid of them is scissors--snip!-- the two halves fall to the ground, and the birds eat the remains. (Just be careful if they are over your head, and keep your mouth closed!)

Carla in Sac

    Bookmark   April 28, 2009 at 11:36PM
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I pick them off and pitch them into the lake. (The garden is at the shoreline) On occasion there will be a thrash and a splash in the water as a bass or walleye participates in this total organic feast!

Gee, that feels good!

    Bookmark   April 29, 2009 at 7:55AM
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Bets(z6A S ID)

Just be careful if they are over your head, and keep your mouth closed!


I remember them in my mother's garden, but have not seen them in mine (Thank goodness!) I plan to plant dill and fennel to attract beneficial insects and to use in the kitchen. But I do have BT on hand, just in case....


    Bookmark   April 29, 2009 at 8:22AM
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austinnhanasmom(5 CO)

In my quest to companion plant, to hopefully protect my tomatoes from hornworms, I found people on this site that are hornworm advocates. I just searched again and read that the adult moths pollinate difficult to pollinate flowers??? Personally, I just hated the idea of my kid repeatedly nabbing a tomato, covered in dust, and then me yelling DON'T EAT THAT YET!! Was futile. He became ninja-like and snuck the fruit!!

My goal is to also garden organically and attract beneficials. Last year, DH "weeded" and somehow a pregnant praying mantis was trapped in the debris. Poor thing ended up in a garbage can, which is where all her babies were laid. I almost cried. The teachable moments began when my son asked what the two bugs were "doing" (he has incredible eye site!!) and then I had to explain what happened to the mom/babies. I feel like I have to do EXTRA EXTRA EXTRA this year in restitution.

    Bookmark   April 29, 2009 at 9:26AM
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tomakers(SE MA Zone 5/6 or ?)

Actually, I like to see the mature moths(they look like and can be mistaken for humming birds), but NOT on MY tomatoes.
Where do I get a black light???

    Bookmark   April 30, 2009 at 1:00AM
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medcave(8 Tx)

I just ordered a 51 led bulb blacklight flashlight off eBay (see link below).

Here is a link that might be useful: eBay

    Bookmark   April 30, 2009 at 8:02AM
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The tomato hornworm and the tobacco hornworm are two different species. The tobacco hornworm is actually the one most commonly found on tomatoes.

Tobacco hornworm

Blacklight LED's are great...I bought some 5mm UV LEDs from where they are super cheap (even the shipping is cheap).

You can buy fluorescent blacklights at Walmart in the fluorescent section.

I like to rear my hornworms to adult moths (as well as some other caterpillars). I pick them off the tomatoes and feed them older foliage that I don't mind picking off.

I found a couple cabbage loopers and armyworms on my tomatoes last small numbers, they don't do much damage. Hornworms must be removed as soon as they're found, and either killed or reared to adults (and maybe the adults should be released a good number of miles away from your garden).

Anyway, just my input on the subject. I've never tried shining a black light on a hornworm, but I can try it this year if I find any on my tomatoes.

    Bookmark   April 30, 2009 at 10:48AM
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Hey Guys; The blacklights are to see the Hornworms at night,but this only works on the older ones with stripes.There is a better way.
I pinch the first or second "true leaf" stem hard enough to crush the epidermis but not so hard as to break off the leaf. This causes the tomato plant to produce an over abundance of Protinase Inhibitor's (yes, the same ones that are used in the treatment foe AIDS).This is deadly to the developing hornworm.
I got this technique from Barbara Damrosch, who will be a speaker along with her husband, Eliott Coleman at the summer conference at SSE.
Before you knock it you should try it.It needs to be done while the plant is 4-8 inches tall.

    Bookmark   April 30, 2009 at 10:54AM
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I did a search on "proteinase inhibitors and hornworms" and did indeed find some neat stuff. I don't know if pinching a single stem would do the trick, but it is amazing what responses plants are capable of. One article about tobacco talked about the plant emitting predator attracting chemicals in response to being chewed on. My tomatoes must be the dumb varieties because hornworms seem to do a pretty good job chomping on them.


    Bookmark   April 30, 2009 at 2:14PM
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Yah break out the blacklight and crank Iron Butterfly's "In a Gadda Da Vida"

    Bookmark   April 30, 2009 at 4:34PM
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countrydoc20(z9 CA)

I originated the idea of UV blacklight to find tomato hornworms. I had a bad infestation in my garden, and spent about an hour in daylight to find 8 worms. That night, on a whim, I tried my blacklight, and found about 18 more of the voracious critters.

This is like what scorpion researchers do in the desert, where they use a UV blacklight to spot scorpions on the sand.

I wrote in to Mother Earth News with the idea, and it was published, but it seems not to have reached the community awareness very well. Try it! It works!

    Bookmark   June 21, 2009 at 10:05AM
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ditnc(7 NC)

I remember how freaked out I get each time I see one. NO WAY could I touch the thing!!

I plan on using l-o-n-g tongs to capture the ugly creatures....while playing In a Gadda da vida with a black light ;)

    Bookmark   June 21, 2009 at 11:13AM
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Re: the capture of the hornworms, I too can't stand the sight of them much less touching them. Once they start appearing, I use an old BBQ two-pronged "fork" to lift them off the leaf and then ceremoniously dump them into a small bucket of water.

    Bookmark   June 21, 2009 at 5:28PM
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kiddo_1(NE OH 5)

I have occasionally found hornworms on my tomatoes. But in each instance I found it because it was almost totally white being covered with parasitic wasp eggs. I just relocate the worm to the back of the yard and let the beneficial wasps do what they do best.

    Bookmark   June 21, 2009 at 6:18PM
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yardenman(z7 MD)

If you find a hornworm with eggs stuck to its back, just put it on a weed away from the garden. The parasitic wasp larvae will kill it soon enough and grow to find new ones. If it doesn't have any, just step on it.

Don't worry, the hornworm won't bite, and if you are still worried just use a rubber glove to handle it.

    Bookmark   June 22, 2009 at 6:22AM
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How long does it take for the wasps to kill the infested worm?

    Bookmark   June 22, 2009 at 8:49PM
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Here's a video I shot of a hornworm attacking a large set of tweezers.

Here is a link that might be useful: Hornworm video

    Bookmark   June 23, 2009 at 3:46AM
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home_grower(SoCal Z9 S18)

That's a quick little buger.

Medcave thanks for the link. I ordered a 21 LED flashlight. It looks like I will need to hit the local swap meet in search of a velvet elvis painting

    Bookmark   June 24, 2009 at 3:04AM
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Unfortunately all black lights are not created equal. I have a black light and the hornworms glow bright green against the non-glowing foliage. I got a whole lot of the very hard to find small ones off last night. But this was my 4th UV light and the prior ones did not work. The "black light" bulbs (either incandescent or fluorescent) with the black coating - worthless except for fluorescent Elvis posters. The little LED flashlight the TSA uses to look at your driver's license? Also worthless - puts out WAY too much visible light. What you need is the type that you can use to make fluorescent minerals fluoresce. These are made from special quartz bulbs (glass filters out UV) and a fairly expensive black filter (again, made out of quartz glass) and a power supply - battery or otherwise. These will cost either a lot, a whole lot, or a really whole lot. I think mine was $80 Although I have seen UV flashlights now used for scuba diving at night which I haven't looked up so they may have decent LED ones now but the key is still the expensive filter that blocks the visible light and lets you see the relatively faint glow.

    Bookmark   August 15, 2014 at 9:54AM
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What you want are short wavelength ultraviolet lights. The LED ones don't get any shorter than medium wave. I don't have much experience using UV on hornworms, but this message thread intrigued me. I found a hornworm and tried my LED UV light on it with no effect.

After reading fotogreg's post I did some research. I use to have one of the mineral-grade UV lights when I was a kid. It was bell shaped with a flat filter that could be removed. It was AC only and cost 15 dollars. (Candy bars were a dime at the time.) You could remove the filter and smell the ozone being generated by the mercury vapor bulb. It came with a clear piece of plastic that you could use to filter out the short waves and see a dramatic drop in the number of things that would glow.

The take away from my first UV lamp is that shortwave filters are flat and cannot be bent. The filter is used to remove visible light. The filter is the most expensive part of the UV light.

The mercury vapor bulbs are mass produced to use in sterilizers. They are mostly quartz, but there is one made by Philips that uses borosilicate glass (Pyrex).

The mercury vapor bulbs produce ultraviolet light with a wavelength of 253.7 nanometers. This is bad for your eyes and will cause sunburn.

There are many mineral-grade UV lights for sale on eBay. They are usually low wattage with a small filter window. Another use for UV lamps is in a fixed mineral display. These will be higher power and designed to run for longer periods. There is one home-built lamp on sale that is 100 watts and described as a "UV death ray!" It uses the best UV filter available, the Hoya U325c.

I am considering buying a $45 UV lamp from this seller:
UV Lights Biz 2012

Note that these lamps become less efficient over time. (> 10,000 hours or so). The quartz in the bulb absorbs mercury and starts blocking the UV. The filter starts blocking UV, too, though a process called solarization.

    Bookmark   August 23, 2014 at 1:05AM
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