Monday, March 14, 2011

Controlling Tomato Horn Worms Organically

I was recently asked about organic solutions to tomato hornworm infestations. They can be controlled through hand picking, thinking like an ecosystem, using crop rotation and soil solarization, as well as growing super productive tomatoes that can tolerate some predation.

Hand picking is often all you need to do. Go out after dark or before dawn with a flash light. Horn worms, slugs, and many other pests do most of their feeding in the dark. You can carry an empty plastic container of some kind, like what peanut butter or yogurt comes in. It will need to be big enough to contain all your “finds.” Then simply pick the creatures off the plants, drop them in the container and put the lid on. If you have chickens, ducks, or guineas--offer them your finds. You will soon learn which sorts of pests they will be happy to devour and which they detest. (By the way, guineas and runner ducks are supposed to get along very well with gardens—you could simply let them into the garden when pests get out of hand, and they will devour the bugs and slugs. Chickens are a little more problematic, leave them in the garden a minute too long, and they will eat your plants down to the roots. ) If you don’t have hungry birds, the container can be left in a sunny place for a few hours, or the contents can be dropped into a bucket of water. These pests are high in nitrogen so consider adding them to the materials used in the compost hole method:

When you think like an ecosystem, you know that every source of protein and be eaten by something. This is as true for tomato horn worms as it is for any other pests. Toads, wasps, and skunks are your friends--they will search out tomato hornworms and devour them. Skunks might seem a little hard to live with, but if you talk softly and avoid sudden movements when they are around, they grow accustomed to your presence and generally make good neighbors. Loud noises and sudden movement, on the other hand, can trigger their well known defenses.

As crazy as it may sound, wasps also like to be talked to softly, and they dislike sudden movements. When a wasp flies up near you, hold still and let it “scan” you. It will fly back and forth and up and down very close to you, and memorize what you look and smell like. It might even land on your hand or shirt briefly and walk around. If you are calm and quiet, there are usually no negative consequences. They learn who lives near them and can tell friend from foe. I once had a wasp nest over my door, and my son and I, as well as our friends, came and went without any problem. But one day a neighbor came to the door and started yelling and the wasps all flew down and chased her away. Having wasps for friends’ pays very nice dividends. Wasps’ most favorite food is caterpillars. They will seek tomato hornworms, chew them into pieces, and carry any pieces they don’t immediately devour back to their nests for their young. I find wasps to be very lovable neighbors for a number of reasons.

Toads are great in the garden also. They eat caterpillars, slugs, and many other garden pests. Like all wildlife, they prefer slow movements and soft voices. However, unlike skunks who will most likely make their home in a wild place, and wasps who can make their homes just about any place, toads may need you to design some habitat just for them. For more information on developing toad habitat see my article: “Hedging for Amphibians.”

Crop rotation can help control tomato hornworms. Plant your tomatoes as far as you can from the spot where the tomato hornworms bothered them last. The hornworm pupa over winter in the soil. When spring arrives the moths emerge and lay their eggs on your young plants to start the cycle all over again. If you have enough room to let some of the garden be fallow for a few months, do a little research on soil solarization: If you set up your solarization in the fall, or before it gets warm in the late winter or early spring, it should rid your ground of the horn worms you have now. However, the adults can still fly in and lay eggs. Some people find that planting garlic and basil can help detour the moths. But this only works if the local population is not too high. The moths’ biological imperative is to find an appropriate home for the next generation. If there is lots of competition for those homes they will hunt for good spots all the harder.

Last but not least you can try growing some super tomato plants that can produce enough food for you and the hornworms. Start with the compost hole method mentioned above: Tomatoes thrive on soil prepared in this way. Choose indeterminate heirlooms (see: for more information on what this means) and don’t pinch them back or prune them unless it is really necessary (your hornworms will take care of the pruning for you). These tomatoes can out grow a moderate horn worm infestation. You may still need to do some hand picking—and encourage predators is always a good idea, but there should be enough for everyone. (This is exactly what I did last year. Even with a moderate hornworm infestation, by the end of the summer I was pruning armloads of new growth off the tomato plants every week. There was more than enough for everyone!)

If you have any questions, tips, or comments--please feel free to share them here, on my face book photo albums, or on any of my face book threads. You will need to send me a face book friend request, before you can comment there, but I do generally add everyone who asks.

Happy gardening!

Copyright 2011, Harvest McCampbell


Anonymous said...

Thank you. These tips are a big help, and just what I was looking for. - dominic

Harvest said...

You are so welcome, thanks for your good words . . .

Anonymous said...

Such great advice.