How to Kill Caterpillars Organically

Several weeks ago I put in our fall crop of lettuces. Here in Northern California we get two lettuce growing seasons, in the spring and fall. They were doing beautifully until one day I found that something was ravaging them and leaving behind little mounds of poo.

Healthy plant

Caterpillar ravaged plant

Caterpillar droppings

The culprit I discovered was a little green caterpillar, about an inch long. I pulled off and squished 20 of the suckers in our little lettuce patch. The next day I pulled off another 10. The following day I found a whole bunch of babies. Grrrrr. What to do?

Here are two solutions. The first is probably the most effective. Spray the plants with Bacillus thuringiensis, otherwise known as “BT”. BT is a naturally-occurring soil bacterium that produces poisons that will kill the caterpillars when ingested. It is completely non-toxic to humans and animals.


The second solution is to place a cardboard plant collar around the plant. This dissuades the caterpillars. Don’t ask me how, it just does. The plants with the collars weren’t bothered by the bugs. Those without were.


6 thoughts on “How to Kill Caterpillars Organically

  1. When you have a bug infestation, you can pick a bunch of the bugs, smush them good (as in a blender), then add a little water and let the mixture set a few days to make worm soup. Then strain out the solids, and spray your plants with the juice. The juice contains a live culture of whatever smaller varmints that the healthy bugs have been fighting off. The high concentration of varmints in the soup is usually enough to overwhelm even healthy bugs.

  2. Hi Elise,
    Thanks for reminding me again the existence of your website. Sorry it’s been out of my mind..I’m glad that I’m back checking it out again now. I know I won’t be much help in solving your caterpillar’s problems :-) it’s not my forte, but I can suggest to visit this blog:
    They seem to know what to do with everything gardening and sustainable living. Good luck…see you again soon.

  3. Thanks for the tips. These Cabbage loopers (sounds like what you have, too) are destroying my flower garden as well. The insecticides just dont seem to do the job. The tips I found here sound great and a whole lot safer!

  4. What do I do with the cardboard when I have to water the lettuce? Can I just leave them to get wet? Once dry will it still be effective?

    Yes, you can just leave the cardboard there. If it’s a good sturdy cardboard, it should hold up pretty well even with the watering. ~Elise

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