The Tomato Hornworms Have Arrived

 

It is hard to tell in a photo,
but this hornworm is only about an inch long.
They can grow to be around 5 inches.

I discovered the first of this year’s tomato hornworms in my garden a couple of weeks ago. I found the first one quite by accident, which isn’t the way I normally find them. Usually I notice the missing leaves and sometimes the tell-tale caterpillar poo, which leads to a search to find the hungry invaders. This time I was eye-to-eye with the green creature. It had not yet done much in the way of damaging the plant as it was less than an inch long – small compared to what they can be. I looked around and found a second one on the same plant. I have been scouting for them ever since – on all 14 tomato plants – and so far so good.

Hornworms also can be a problem for tomato relatives like eggplant, peppers and potatoes, so it is a good idea to check them as well.

It can take a while to find them when I start looking for the nasty green worms because they blend in perfectly with the stems and foliage. Each year I have to retrain my eyes to spot them quickly. Hornworms have ravenous appetites and eat so much so quickly that they grow really fast. If I had taken a couple days longer to detect them, they could have easily been the size of a finger, and perhaps devoured much of the plant they were munching on.

How do you recognize a tomato hornworm? How do you manage them?

Here's a little information from the UC Davis website http://www.ipm.ucdavis.edu/PMG/GARDEN/VEGES/PESTS/hornworm.html

"Tomato hornworms of all sizes have a distinctive horn at the rear end. If you find them early on they are small, but mature caterpillars are very large - up to 4 inches long. Tomato hornworms are likely to be the largest caterpillars you will see in the vegetable garden. Their striping pattern makes them hard to spot despite their size. Large, black droppings on the ground beneath tomato plants or on the leaves below where they are feeding usually indicate the presence of hornworms. The adult moths that are responsible for these worms have a wingspan up to five inches.

Damage by hornworm larvae (the worm/caterpillar) is usually most common in midsummer, but there may also be a small population peak in the late summer. Infestations tend to be more severe in warm inland areas such as the High Desert. The larval form is the only stage that causes damage. The eggs are laid singly on leaves. The larvae feed and grow, and then burrow into the soil to pupate. The adult/moth develops over the winter and emerges and the cycle continues. Entire leaves and small stems may be consumed by the larvae. Large pieces from green or ripe fruit may also be chewed.

To manage hornworms, handpick or snip hornworms with shears. Hornworm eggs can be attacked by Trichogramma and the larvae of Hyposoter exigua - two types of parasitic wasps - which can be purchased through various catalogs and released into the garden. There are also several general predators such as praying mantids to help keep populations under control. Bacillus thuringiensis (Bt) or Spinosad are both effective against smaller larvae. Discing or rototilling the soil after harvest destroys the pupae and helps prevent adults from developing."

I tend to handpick the hornworms from the plants, and then feed them to my chickens. It is important to keep looking and not assume there are only one or two. It is best to look for them early in the morning, because they tend to hide out during the heat of the day. Look along the stems and under the leaves, especially near the ends of the branches and near where damage has been found. If you notice the droppings, look above that area. Tomato hornworms used to scare me so I would snip them with shears, but the disgusting green goo they leave behind is not very appealing. I eventually learned to put on a pair of gardening gloves and simply pick the worms off the plant.

Chickens enjoy feasting on tomato hornworms, so if you happen to have chickens, it's a great way to dispose of the worms once you have removed them from your plants. If you notice the eggs or pupa (cocoon), destroy them before they develop into the dreaded hornworm.