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Q. Do tomato hornworms turn into a pretty butterfly? I won't feel so
bad squishing them if they don't. Also, I had some moonflower plants (the
poisonous kind that are related to the wild variety, which grow in pig/cow
pastures). Anyway, I had some kind of green hornworm eat every leaf off
every plant. How can a hornworm eat a poisonous plant and not die? --
Linda W., Plymouth , Ind.
A. Tomato and tobacco hornworms are large caterpillars, up to four inches
in length. The prominent "horn" on the rear of both gives them
their name. They can quickly defoliate tomatoes, potatoes, eggplants and
peppers. Occasionally, they may also feed on green fruit. You're likely
to notice the damage before you see the culprit. Hornworms are often difficult
to see because of their protective coloring and their tendency to feed
on the interior of the plant where they are protected from the sun and
predators.
The tobacco hornworm larva is generally green with seven diagonal white
lines on the sides and a curved red horn. The tomato hornworms have eight
V-shaped marks on each side, and their horn is straighter and blue-black
in color. The adult of the tobacco hornworm is the sphinx moth. The five-spotted
hawk moth is the adult of the tomato hornworm. Both moths are stout-bodied,
grayish-colored insects with a wing spread of 4 to 5 inches. They're not
exactly pretty butterflies but are large and striking. A quick search
on the Web proved there are many excited butterfly/moth fanciers that
think the hawk moths are fascinating!
If you're interested in tomatoes and not in moths, you can control them
with the following methods:
Handpicking: The large size of hornworms makes it easy to get hold of
them. Once removed from the plant, they can be destroyed by squishing
them, snipping them in half with shears or dropping them into a bucket
of water.
Tilling: Turning up the soil after harvest will destroy any pupae that
may be there.
Biological controls: Bacillus thuringiensis, or BT (e.g., Dipel, Thuricide),
is also considered effective, especially on smaller larvae. Follow label
directions. Natural enemies, such as the parasitic wasp that lays its
eggs on the hornworm's back, are common. If you come across a hornworm
with something that looks like fuzzy pieces of rice on it, leave them
in the garden so the emerging wasps can parasitize other hornworms. The
larvae feed on the hornworm.
The answer to your question about why hornworms can eat poisonous plants
is just that those plants aren't toxic to them. Some birds, animals and
insects can eat many plants that would be toxic to humans.
Q. I was wondering if you could tell me what is making my apples -- red
and golden delicious -- have places on them that look like bite marks.
And where they have these marks, the apples do not grow right. If they
have very many, the apples don't get much bigger than a walnut. They don't
seem to be worms. On one tree, most all of the apples didn't mature at
all. I spray them in the bud stage, and, after petal fall, I try to spray
them about every two weeks. The apples were a bit wrinkled up. What kind
of spray do I use to stop this? -- Kenneth Rippy, Warren , Ind.
A. Your description sounds like plum curculio. See the answer below for
a description. Adult control is accomplished by insecticide applications.
The typical multi-purpose fruit sprays do not provide very good control
of plum curculio. Next year, apply an insecticide containing the active
ingredient "esfenvalerate" at petal fall. This insecticide is
available at most garden centers under various trade names, but be sure
the active ingredient is correct and apple is on the label. Starting next
year, pick up and destroy the apples that drop in June because some of
these will contain plum curculio larvae. This is an opportunity to break
the insect's life cycle and will reduce damage in future years.
Q. Would you please give me answers to the following questions: are tomato
plants self pollinating; and how does a worm get into a peach? -- Lovell
Caudill, Linton , Ind.
A. You can grow one tomato plant and have fruit. Tomatoes do not require
another plant for cross pollination. They do, however, have heavier fruit
set with help from external forces.
Tomatoes need help from bees, especially sonicating bees (vibrating wing
muscles that cause the entire flower to shake), or from wind or other
mechanical shaking to produce a truly heavy crop. For many years, greenhouse
growers employed humans with electric vibrators (one brand name Electric
Bee) to accomplish pollination. Today, these have been mostly replaced
with cultured bumblebees, which do it more efficiently and cheaply.
Several larvae feed on Indiana peaches. Let's consider two of the most
common. There are several generations of the Oriental fruit moth during
a growing season. The first tunnels into the end of peach twigs, causing
them to wilt and die. Later generations feed on fruit and twigs. Larvae
commonly bore right to the center of the fruit and feed around the pit.
This can cause the fruit to drop. The wounds often exude a gummy substance,
and the area around the wound rots. Damaged fruits that remain on the
tree are distorted. Occasionally, the larva may tunnel into the fruit
through the stem. In such instances, there may not be any apparent evidence
of how the larvae entered the fruit after it is harvested.
Pheromone traps are available for this insect to monitor moth activity
and effectively time sprays. Traps are placed in the inside of the tree
at eye level or higher, just before bloom. For backyard trees, a single
trap can be used, and an insecticide treatment is made at petal fall if
the insect is detected. Commercially, sprays for the first generation
should be applied six days after peak flight, which coincides with peak
egg laying . This often coincides with the time for plum curculio control.
Sprays for the second and third generations need to be applied three days
after peak flight. Depending on the anticipated harvest date for the fruit,
sprays for the third generation may need to be adjusted or omitted in
order to meet the necessary preharvest interval requirements for certain
insecticides.
The female plum curculio, the most common larvae found in Indiana peaches,
cuts a hole in the fruit with her mouthparts and hollows out a small cavity,
then turns and deposits an egg in the cavity. She then cuts a crescent
-shaped silt, which extends beneath the egg so as to leave the egg in
a flap of flesh. Injury will appear as a one-eighth-inch crescent-shaped
cut on the fruit.
This prevents the egg from being crushed by the rapidly developing fruit.
After about five days, the larvae will hatch and burrow into the fruit.
The larva is a legless, grayish-white grub with a brown head. Its length
will be about one-third inch when full grown.
When the larvae are fully developed, they will leave the fruit through
clean exit holes. No frass or webbing will be evident. See the answer
above for control measures.
12-1-05
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