Here we go again!
It seems to be that time of the year when the tomato hornworms make their
annual appearance and start busily munching away on my tomato plants. So far,
in the past couple of weeks, I have found four of them. They can also be a
problem for other related plants like eggplant, peppers and potatoes – so far
so good on those.
It doesn’t take
too long to notice the tell-tale signs of these hungry invaders. The foliage at
the ends of the branches on the affected plants will eaten, and not far below
the missing leaves is where you’ll find the droppings (caterpillar poo). If
left very long, entire branches, and even entire plants, can be devoured.
With a lifetime
of gardening experience, I know to start looking for the nasty green worms
around mid to late June and throughout the growing season. At first they are
tough to spot because they blend in perfectly with the stems and foliage. It’s
best to catch them early on when there is only minimal damage to the plants –
only a couple of bare stems. So far this year, as I said above, I have found a
total of four hornworms, a couple of smallish ones and two rather large ones. The
small worms were only about an inch long, which means the eggs they came from
had just recently hatched. They have ravenous appetites and eat so much very
quickly that they grow 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 on.
How do you recognize a tomato
hornworm? How do you manage them? Here’s a little information from UC Davis’s
Web site (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
To manage hornworms, handpick,
or snip hornworms with shears. Hornworm eggs can be attacked by Trichogramma
and the larvae by 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 effective against smaller larvae. Discing or rototilling after harvest
destroys the pupae in soil and helps prevent adults from developing.
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.
