A friend who is having problems with caterpillars and tomato horn worms eating holes in the leaves of his cabbage, kale, tomatoes, and other vegetables in his garden called me to see if I had any organic suggestions for how to deal with them that was safe to use and would not harm the beneficial insects in his garden.
A few years ago I found a product called Bacillus Thuringiensis which is a bacteria that attacks caterpillars, loopers, cabbageworms, hornworms, leaf folders and leaf rollers yet does not harm other beneficial insects like nematodes, lady bugs, bees, etc., that we want in our gardens.
BT is a completely organic method of dealing with these insects safely. An 8ounce bottle generally runs around $10 and will last you for several applications.
BT is extremely easy to use, although the instructions on the labeling are a little misleading. According to the instructions you can use between ½ to 4 teaspoons of the product mixed with 1-gallon of water, but I can guarantee that using a mixture that weak will not have any beneficial effects. There simply is not enough of the bacteria contained in the dilution then to do any good. They also do not warn you in the instructions not to use chlorinated water when mixing the product.
Remember this product contains a live bacteria, we do not want the chlorine in the water to kill the bacteria before it has a chance to kill off the caterpillars and horn worms. Chlorine kills off both good as well as bad bacteria.
If you do not do rainwater harvesting to have a supply of un-chlorinated water, to remove the chlorine from city tap water you can either fill a bucket with water and let it sit uncovered for 24-hours to off-gas the chlorine, or you can aerate the water with an aquarium air pump and an airstone to remove it in a couple hours.
Mix 3 to 4 teaspoons of BT with 1-gallon of un-chlorinated water. Spray the solution generously all over the plants, both on top of and underneath the leaves. The bacteria will not harm the plants or other beneficial insects but when it comes in contact with caterpillars, loopers, cabbageworms, hornworms, leaf folders and leaf rollers, it enters their bodies kills them very quickly. It is basically a flesh-eating bacteria that is specific to those insects.
You will need to retreat the plants about every 2-3 weeks to make sure that they do not come back.
One thing to keep in mind though is that this is the hot part of the year so you do not want to spray any liquids onto your plants in the daytime that may burn the leaves. So, during the summer when these particular pests are most prevalent, make sure that we do the application either early in the morning when it is cool or later in the evening after it cools down and the leaves do not have direct sun on them.
BT is the best organic method that I have found to get rid of caterpillars and horn worms in the garden. It is also effective for tent caterpillars and gypsy moths in fruit trees.
I highly recommend BT as an organic solution for these pests in your garden.
Until Next Time,
Aloha & 73