Gayla Trail

Gayla Trail

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Q: Do you have any suggestions on how to keep caterpillars from eating all my herbs and tomatoes? They have attacked my sage especially.

ANSWER:

I have to admit that I was initially surprised by your question. Not about the tomatoes, as they are a popular food source of tomato hornworm (Manduca quinquemaculata) and Colorado potato beetle (Leptinotarsa decemblineata) larvae. What shocked me is that the greatest damage is to your sage plant(s). Common garden sage has a chemical composition that makes it unpalatable to most garden pests. As a result my sage plants have never suffered insect damage, even when their neighbors are overrun and decimated.

See how to use items from your kitchen to keep squirrels and other pests away.

However, in pondering your dilemma, I recalled reading about caterpillars munching on alkaloid-laden plants that they would not normally touch as a way to self-medicate against parasites. I wonder if that’s what is happening in your garden? Another possibility is that the weather has brought an infestation of a specific insect whose population was so insignificant in the past that its damage went previously undetected. 

Or perhaps an atypical pest has found its way to your garden, one that doesn’t mind the taste of sage. I have also found that slugs and earwigs have run amok in my own garden this year and are chomping on plants that are normally immune, simply because there are so many of them and competition for food is fierce. I liken the garden this year to a popular restaurant that is overbooked — the yummiest treats at the buffet table are dwindling. It’s hard out there for a pest!

Regardless of the cause, you want answers and I want to help you. Fortunately, there are solutions.

Organic Control

  • My first suggestion when it comes to pest control in an organic garden is to deploy the five-finger solution: aka handpick and squish ‘em. If you’re squeamish about squishing you can always wear gloves and drop them into a bucket of soapy water. A few short squishing sessions over the course of a week may be enough to eradicate the problem. Follow that up with random spot checks. Look underneath the leaves for eggs and caterpillars as well as their frass (aka caterpillar poop) as proof of their existence, even if you don’t see them.
  • You can’t squish larvae that you can’t see, in which case you might try simply cutting back the damaged plant and destroying the foliage (burn it). Fortunately, there is enough time left in the season for your sage to recover and offer up a second harvest.
  • Plant umbelliferous flowers (i.e. dill, fennel, parsley to name a few) that will attract parasitic wasps to your garden. Interplant them around and among the plants that have sustained the most damage. These wasps will lay their eggs inside the caterpillar’s body, eventually killing the host.
  • When all else fails you can try applying Bt aka Btk (Bacillus thuringiensis) a bacterium that is considered harmless to humans but acts as a poison against caterpillars. I mention this option because I know it will come up but do not recommend it for a few reasons. Not all caterpillars are harmful in the garden and while Bt is selective in that it only kills caterpillars, it is not selective in the caterpillars that it kills. Anything that eats the leaves of infected plants is fair game. I would also argue that no spray is completely benign. Since you are spraying directly onto the leaves of an herb, I’d consider whether this is something you are comfortable in ingesting: safe or not.

Garden authority Gayla Trail is the creator of YouGrowGirl.com.

7 Comments About this Article

  • GardenGoddessinmaking
    ok I was hoping for better resoloution to the posting gardners issue, as I too had that same issue last year! seems as though Alice in wonderland is not the only one dealing with those horrible multi-legged green monsters! I tried several organic treatments to no avail and finally yanked up allmy tomato plants flinging them over to the burn pile!

    Posted 1 year ago

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  • Amy
    Caterpillars grow up to be beautiful butterflies and moths.

    Posted 1 year ago

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  • Kimberly Nowlin
    I don't care about beautiful Butterflies, What I care about is my tomatos!!!! They are my salad mixings, and its like i've got a bunch of thieves stealing my tomatos death to them all

    Posted 1 year ago

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  • Suzanne Sicard
    Tomato Hornworm, and Tobacco Hornworm both attack tomato plants and do severe damage. BT Bacillus Thuringiensis is the best bet to get rid of them, before they annihilate your crop. BT is considered Organic because it occurs naturally in the the soil, and has no effect on humans, only moth/butterfly larvae. BTW Amy, larva that attack tomato plants do not grow into beautiful butterflies or moths, they actually grow in to very homely looking moths. I am curious about the caterpillar found on sage, because I just found (never have seen caterpillars on sage before). Sage is commonly used to repel caterpillars and moths. The one I found is small and green with a long black spike on it's tail end. I'm going to keep to see if i can ID it. It is very odd to find it on sage.

    Posted 1 month ago

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  • Jeanne Gibbons
    I have a large nest of them in one of my trees and it is too high for me to reach. Does anyone have an idea for removing it from my back yard? Thanks, for your help!!!

    Posted 1 month ago

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  • Joy of Camden
    A friend recently told me to plant Basil seeds around my tomatoe plants and I would have no pests bothering my tomatoes...she was right...for the first time, I have had a great crop of tomatoes with very little damage done to the fruit! And I can easily pick fresh Basil when I pick tomatoes!

    Posted 3 weeks ago

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  • BridgeJet23
    I had 4 tomato horn worms on my cherry tomato plant that's in my screened-in porch! I saving them in a bucket, just plucking the lower leaves of my tomato plants out in the garden and pinching back the suckers to give them for food. They will turn into the hummingbird moth which is an excellent pollinator.

    Posted 3 weeks ago

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