The dreaded hornworm. Both tomato hornworms and tobacco hornworms can attack tomato plants in the garden. A single hornworm can wipe out a plant in a matter of hours, and several of them can decimate an entire row of tomato plants in no time!
If you suddenly find your lush tomato plants have become nothing more than stems, most likely a hornworm is the culprit. In fact, it’s a good idea to examine your plants a couple of times during the day, if at all possible, to head off the devastation. They often start near the top of a plant, so the tell-tale bare stems are fairly easy to spot.
The common advice seems to be that gardeners should rotate their tomato crops in order to prevent infestation, since garden soil can harbor the eggs from one season to the next. To be honest, I haven’t found that to be much help. Hornworms showed up the first year in soil that had never grown tomatoes before, and they continue to find my tomatoes even if I move them.
The best way I’ve found to deal with them is to watch carefully for damage. If any damage is seen, start searching for the hornworms. They can be very hard to find, since they are fat and green and blend in perfectly among the tomato stems. During the heat of the day, they are usually hidden on the undersides of stems. Look just below the damaged area and you will mostly likely find them there. I always handpick the caterpillars and destroy them, and follow it up by spraying the plants with BT (Bacillus thuringiensis).
BT is a naturally occurring bacteria that is found in soil and caterpillar guts (so I’m told). When sprayed on tomato leaves, the hornworm caterpillars eat the leaves but can no longer digest, and they die within a day. Damage to the plants is very limited after spraying as well. I don’t use pesticides or other artificial chemicals on the homestead, but BT is not a man-made pesticide. It’s an organic type of control that won’t harm beneficial insects, birds, or other animals and doesn’t leave any residual effect on the tomatoes. It is approved for use in certified organic produce gardens.
In fact, it can also be used proactively. If I’m not going to be able to check on my garden, or if I’ve already started seeing hornworms, I’ll go ahead and spray BT. Check the label since it is mixed differently depending on what kind of pests you are treating. I spray the leaves either in the early morning or late evening (I don’t like to have moisture on the leaves during the hottest part of the day) and from that point on, practice watering only from below. If it rains, it will be necessary to spray more BT.
I bought a bottle two years ago and paid about $10 for it, and it’s still more than half full. A little goes a long way, and it does a great job of protecting against hornworms. Guineas and ducks have taken care of most garden pests for me, but they usually won’t touch the hornworms. I’m told the long horn on the end is a stinger and they can inject a toxin. For whatever reason, the poultry usually won’t try to pick them or eat them, even if I cut one in half and toss it to them. Fortunately my outbreaks are usually limited to no more than a handful of worms at a time, and the BT does a great job of killing any I might miss when picking them off.
(Edited to add — hornworms will attack pepper plants and happily munch them down to nubs too. Since my peppers are usually planted near my tomatoes I keep an eye out for hornworm damage across both areas.)