Tomato Hornworm larvae: sift them out?

donnabaskets(Zone 8a, Central MS)January 4, 2014

Two years ago, the hornworms were awful in my potted tomato plants. Last year, I dug out the top foot or so of soil and replaced it with new. Almost no hornworms last year.

Just wondering. Do you think I could use a compost sifter, run my potting soil through it and back into my pots? (I always renew my potting mix with fertilizer, etc.) Would the sifter be fine enough to get the larvae out? I have seen pictures of them online but really don't have a concept of how big they are.

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digdirt2(6b-7a No.Cent. AR HZ8 Sun-35)

The larvae are hatched from eggs laid on the plant itself, not in the soil. In the soil you will find only pupae and they are approximately the size of the average adult hornworm - 3 to 4 inches - so easy to spot (see pics below)..


Here is a link that might be useful: Hornworm pupae pics

    Bookmark   January 4, 2014 at 1:36PM
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I realize all areas of the country have different garden problems, but aren't hornworms also hummingbird moths? They're one of my favorites and I plant white petunias for them every year. However, I haven't noticed much damage to the tomatoes....

And I live in the country with no close neighbors, so they must be here, somewhere. Also have lots of cabbage moths, but not much cabbage damage. Do they like other plants even more? We have all kinds of plants down by the creek. Just wondered if there were any 'trap' crops that might help.

Donna- Hope you have better luck with the tomatoes this year :)

    Bookmark   January 4, 2014 at 6:35PM
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ZachS. z5 Littleton, CO

Any caterpillars that were on your plants last summer wouldn't make it through the winter, so if you did find one, it would be dead. hornworms pupate in the ground until they emerge as moths. Some moths do overwinter as a pupa, others, as adults. I have no idea about hornworms, so lets just assume its the first. The pupae are, in and of themselves, harmless, but assuming the ones you would find while "sifting" are viable (and in great enough numbers), it could be a potential problem when they emerge, mate and lay eggs on your tomatoes, peppers, eggplant, etc... but I just don't think your going to find that many.

If you didn't notice any hornworms on your plants last year, there probably was only very few, if any. So say there were maybe 5 that pupated in your potting soil throughout the summer. Of those 5, 3 became moths during the same season (since in many cases more than one generation of insect is born in a single season) and flew off. No amount of soil sifting is ever going to find them. That leaves 2 possibly ready to hatch, I don't think that would really be cause for concern. The likelyhood of more crawling over to your 'maters just in time to pupate would be highly unlikely. I'd say your time would be better spent doing other things then sifting dirt (unless you like doing that, then don't let me stop you haha)

Lavender Lass: The tomato hornworm is the caterpillar of a type of hawk moth which are in the Manduca genus. Along with its close cousin, the tobacco hornworm (which grows into the Carolina sphinx moth), they pretty much like to eat nightshades. I don't think they are too particular about what KIND of nightshade, be it your prized heirloom tomatoes, or a patch of bittersweet growing along the creek bed, but as far as I know, that is their (nearly?) exclusive food source. So I guess you could grow a trap crop, as long at it is in the same family as the tomato.

As far as hummingbird moths go, they are in the same family as the hawk moth, but a separate genus I believe. However, In popular language the names are interchangeable.

One more fun fact! You can tell the difference between a tomato and tobacco hornworm by the lines. the former has V shaped markings whereas the latter, just angled lines, but I may have that backwards.

That's probably far more entomology than anyone but a nerd like me would care to know. And at the risk of becoming a Sheldon Cooper, I will stop there.

    Bookmark   January 4, 2014 at 11:00PM
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naturegirl_2007 5B SW Michigan(5B SW Michigan)

Hey ZachS: You've got the markings right. I read a good way to remember the difference between the tomato and tobacco hornworms and have never wondered if I was mixing them up since then.

Just imagine: The tobacco hornworm is a critter that loves to smoke tobacco in cigarettes and puts pictures of the cigarettes (straight lines) on his body...ta da..straight lines= tobacco hornworm

Whereas, the tomato hornworm, is a healthy tomato loving insect who hates smokers, maybe is even an ex-smoker himself and puts crushed, broken cigarette (V-shaped) markings on his body.

And Donna, the pupae are about the size of a longer than average cigarette butt, and dark colored. I'm not sure if they would fit through the screen of your compost sifter if they were lined up just perfectly, but they are easy to see if soil is spread out. Of course, an adult hornworm moth could still come in from elsewhere to lay eggs on your plants even if you eliminated all pupae from your soil. If you are eliminating all the hornworms (larvae) before they pupate, then I doubt it would be worth sifting your soil since there are likely few, if any, pupae in it.

    Bookmark   January 5, 2014 at 4:24PM
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rhizo_1 (North AL) zone 7

Donna, I just wanted to add that I suspect your sifting had nothing to do with the lack of hornworm damage last year.

This year, inspect the upper and lower surfaces of the leaves very frequently for those single, pearl-like eggs. The moths are nocturnal, so the eggs will appear (literally) overnight.

If the eggs are squished regularly, you shouldn't have much of a caterpillar problem. Of course, keep your eyes open for hatchlings, too. Those big hornworms all start out as very teensy little things!

    Bookmark   January 5, 2014 at 4:57PM
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ZachS. z5 Littleton, CO

Thanks Nature Girl! That is a good way to remember. Glad to know I was right about something for a change haha.

    Bookmark   January 5, 2014 at 7:31PM
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donnabaskets(Zone 8a, Central MS)

oops. I used the wrong term. I was referring to the pupae that fall into the soil and overwinter there. Thank you for the link, digdirt. They look quite large, so, as you say, should be easy to spot. I may try sifting, just to satisfy my curiosity, though I had very few last year. Nothing like the infestation of year before last.

Rhizo, I will keep an eye out for eggs. Duh. Never thought to check the leaves.

    Bookmark   January 7, 2014 at 10:52AM
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You might run into some J Beetle grubs, too, although they're more likely to be dead.

    Bookmark   January 8, 2014 at 9:41AM
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runswithscissors(MT 4/5)

I personally don't have tomato horn worms...(oh great! Now I just jinxed myself!) but I've always been curious...

Do they poke you or sting you with their horns? All the books say to "hand pick them". When I look at the pictures I say "Yikes!"

    Bookmark   January 12, 2014 at 1:24PM
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missingtheobvious(Blue Ridge 7a)

runs, the horns are just there to scare you.

Re. hand-picking: I don't want to touch them, so I try to brush them off with a stick. Unfortunately they hold on to the plant tenaciously, so brushing them off is well-nigh impossible except for the itty bitties. Regardless how they get off the plant, if you don't want to squish them, you can drown them in soapy water.

My mother, who is braver than I am, used to cut them in half with scissors (she's 90 and has given up growing veggies). I've always been too squeamish for scissors ... or stepping on them ... or anything that involves touching them (even with a glove or a shoe). I bought some tongs (for getting olives out of deep bottles) but haven't tried them out yet.

But I have been known to cut off the branch they're on and carry them to the front yard and leave them in the middle of the asphalt driveway, where I hope they'll either fry or -- bright green against the asphalt -- be noticed by a passing bird. And I think I may have tossed some out into the street (or maybe that was another bug).

    Bookmark   January 12, 2014 at 1:51PM
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naturegirl_2007 5B SW Michigan(5B SW Michigan)

No troubles from the horns but one has to really grab tightly and pull firmly to get them off of a plant. It's not for the squeamish. And disposing of them is another adventure. Oh, the stories I could tell, but I don't even want to think about some of them. Just be warned that stepping on them just right (or wrong depending on your point of view) can be hazardous to those nearby. Hornworm guts are NOT fun to wear.

    Bookmark   January 12, 2014 at 9:41PM
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Chickens love them - I despise them - but...

Going to make a concerted effort to "harvest" as many pests this spring/summer to feed as a primary protein source for our chickens. Really want to get the chickens off of store bought feed (which I just discovered is GMO corn). Found an excellent book that gives great direction on how to naturally feed chickens.

It is definitely an attitude adjustment to look at garden pests as advantageous when considering them as an excellent food source for our girls. Didn't mean to hijack the thread - just wanted to extend a little hopefulness to those of us bothered by pests such as the hornworm (and the Japanese Beetle).

Posted link to book below.

Here is a link that might be useful: The Small-Scale Poultry Flock

    Bookmark   January 13, 2014 at 1:41PM
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ediej1209(5 N Central OH)

Yep, we "treat" our girls with the hornworms too. So funny to watch them squabble over them!


    Bookmark   January 15, 2014 at 3:02PM
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