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Thumbs Down On Rotten Tomatoes: Getting Rid of the Hornworm

The following is a regular column that addresses basic issues facing the ever-inquisitive back- and front-yard toiler, proffered by someone who knows best; one of the fertile master gardeners from the Berkshire Botanical Garden in Stockbridge. This week, Brian Cruey offers tips on how to keep your tomato plants strong by warding off a large and pesky invader.

hornwormFirst things first: the tomato worm, also known as the tomato hornworm, also know as Manduca quinquemaculata, isn’t a worm at all. It’s a caterpillar and a really BIG caterpillar at that. Think Alice in Wonderland caterpillar big, and you’ve got the idea. It’s no wonder, given its size (up to 4 inches long), that one or two of these “worms” on a tomato plant can wreak a lot of havoc really fast — defoliating leaves, eating new growth, and even eating young fruit, completely destroying a plant sometimes in the matter of a couple of days or even a night. For that reason, I advise to catch them early. Here’s what you should look for:

If you have them, you might start noticing leaf wilt or damage at the top of your tomato plant before you actually notice the tomato worm itself. They attach themselves to the undersides of leaves and tend to feed more at night to avoid the heat, which makes them difficult to spot. Plus they are green and will blend right in with the plant’s foliage, so that doesn’t do you any favors either. You also might start to notice dark green or black gross stuff on the lower leaves of the plant.  You guessed it — that’s their poop.

The nice thing about these “worms” is that they are big and you can catch them easily. If you have read past articles we’ve written here before, you can probably guess that I’m going to tell you to simply pick the caterpillar off of the plant and throw it into that ever reliable bucket of soapy water. In this case, vigilance is really your best weapon. Sometimes going out at night with a flashlight will make spotting them easier.

wormNow, this is where things really get interesting. If you see a tomato worm on your plant that has what appear to be little grains of white rice stuck to its back — leave it. It is doomed and it isn’t going to do any further damage to your plant. Those little white things are actually the cocoons of a type of parasitic wasp that are using the worm for food and eventually will kill it. You actually want all of those little cocoons to hatch and grow into wasps so that they will lay eggs on more tomato worms and help you with your problem. It’s even a good idea to plant companion plants such as Queen Anne’s lace, fennel, and dill around your vegetable garden to attract this type of wasp.

mothIf your caterpillar doesn’t meet its doom via death by soapy water or wasp eggs and makes it to the pupae stage and forms a cocoon, don’t fret. This stage is spent in the top two inches of the soil. If you till your garden after your harvest, you should be able to kill almost all of them that made it into the ground. If they are fortunate enough to make it to adulthood, however, they will emerge in the late spring as a hummingbird moth (also known as the sphinx moth, also known as the hawk moth). To give them their due credit — these moths are great pollinators of night blooming plants.

Oh and that “horn” on it’s posterior is a total fake — perfectly harmless. It’s meant to fool predators but don’t fall for it.

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Posted by Scott Baldinger on 07/31/13 at 09:05 AM • Permalink