Those big green worms you’ll find dining on your tomato plants in the summer? Those are tomato hornworms and while they do turn into the beautiful sphinx moth, they can be rather destructive to your plants if they become infested.
How to Identify Tomato Hornworms
These worms are big, fat, and green. They can reach lengths of up to 5 inches, which is pretty large in comparison to say, a cabbage worm. They feed on nightshades including tomato, potato, tobacco, and eggplant.
They blend in with tomato plants pretty well, like many garden pests and can be hard to spot if you just do a quick once over and there aren’t very many.
Tomato hornworms (Manduca quinquemaculata) do blend well, but once you spot them, they’re difficult to miss since they’re so large. They’re a light green color with white v-shaped markings and black spots. They also have a black spike on their rear (they can’t sting you or anything, it just looks sinister).
Tobacco hornworms (Manduca sexta) are prevalent on tomato plants as well (we actually see way more of these than we do tomato hornworms) and look very similar. The distinguishing difference between the two is a tobacco hornworm has white stripes along it with tiny, dotted black lines. Its “horn” on the rear of it is also red, instead of black.
Finding Out if You Have a Hornworm Problem
Both tomato and tobacco hornworms feed on the entire tomato plant from leaves and flowers to the fruit itself.
Aside from spotting the well-camouflaged creatures that tend to begin feeding on the plant toward the top. So, it is easiest to start looking there and work your way down.
If you see tell-tale holes in the leaves, there are worms somewhere on your plant more than likely. Many times the leaves will become wilted and start hanging down. The fruit can have chunks eaten out of it or even be scalded by the hot sun due to reduced foliage.
If you see any signs of hornworm damage, look underneath the leaves and you will probably find a hornworm hiding out.
You can also look for their droppings, which you’ll see on the top of the leaves. They are greenish or black droppings. You may also see their eggs, which are tiny, greenish or yellowish and oval in shape.
How to Keep Tomato Hornworms Away
Remove Them By Hand
Yep, these large worms are easy to pick off. They can’t hurt you at all, just your plant. Simply pick them off and put them into a bucket of soapy water, or feed them to your flock of backyard chickens. Yes, the chickens can eat the worms, just don’t feed them the leaves the worms are munching on.
It is best to look for hornworms near dusk when they’re more likely to be out on the prowl. Invite the kids out for a worm hunt and gather them all up.
Invite the Ducks In
Ducks, guineas, and even chickens will eat your tomato hornworms… as long as they can reach them. Ducks are typically the least destructive to your garden and won’t peck everything away in the hunt for the delicious worms.
If the worms are too high for the fowl to reach, though, you’ll have to pick them off, as mentioned above, and give them their treat.
Try Companion Planting
Every gardener should utilize the benefits of companion planting. And tomatoes are no exception to that.
Interplanting your tomatoes with things like marigolds, dill, basil and borage can help ward off the bad guys as well as invite the good guys, which brings me to my next point….
Invite Beneficial Insects
Not all insects are bad! In fact, there are many enemies to the hornworm, depending on how large they are. Ladybugs and even lacewings will feed on these big, creepy crawlies at the right stage.
But, the biggest enemy of all are parasitic wasps. You will often see hornworms (and other caterpillars) with little white eggs bunched together on their backs. These are the eggs of the parasitic wasps.
If you see a hornworm with eggs on it, it’s best to leave it alone as it won’t be feeding much longer. This will allow the parasitic wasps (that are tiny and not harmful to humans, by the way) to carry out their lifecycle and continue to keep pests in your garden at bay.
If you really feel inclined to remove the hornworms with eggs on them, don’t kill them. Instead, simply remove them from the garden to a different area so the wasps can continue their lifecycle and help your garden.
Till In The Spring
To till, or not to till, that is the question many of us gardeners have when it comes to the right or wrong way to grow our crops. And well, there are benefits to tilling, and of course, benefits to not.
But, if you decide to till your garden, doing it first thing in the spring can effectively kill up to 90% of the pupae hiding in the upper layers of the soil. It will not, however, kill the hornworms in the larvae stage.
Some is better than none, though, right?
Try Diatomaceous Earth
Diatomaceous earth, or DE for short, can be a great addition to the garden. But, it does have its downfalls.
DE scours an insects outer layer off as it crawls across the substance. If you have a particularly wet season, it won’t work well unless you apply it regularly after every rain.
It is inexpensive and will not hurt your plants. It can be used in large quantities without hurting your plants or the health of your soil. However, it is not a selective insecticide.
So, if you use it, beware that you are also likely killing off beneficials in the garden. If you see hornworms and just don’t want to pick them off, you can sprinkle it on them and on the area of the plant their on and it will dry them out.
Just… be careful, use this sparingly and not as a first line of defense.
I’ll be the first to admit chemicals of any kind are not my favorite way to control pests in the garden. But, desperate times call for desperate measures.
Bacillus thuringiensis (or Bt for short) is a microbe that naturally occurs in the soil. It is an organic compound and can be sprayed as late as harvest day with no ill effects.
This spray is effective at killing worms and caterpillars, so if you raise butterflies (like monarchs) you may want to avoid it as it is not selective.
Completely Remove Plants at Harvest
When you’re done harvesting your tomatoes, remove the entire plant from your garden and dispose of it (not in your compost) if it had hornworms on it.
Many people will throw their plants in the compost or till them into the garden, which is great in theory. But, if you had hornworms on the plant, you’re just perpetuating the cycle. It’s better to destroy the plant so that you aren’t unknowingly allowing the lifecycle of the hornworm to continue once spring weather thaws out that soil.
Hornworms, like all garden pests, can be a total nuisance and pain. But, there are ways to naturally keep them at bay in your garden.
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