Identifying and Managing Pesky
Caterpillars in the Garden
By Mary Bernard, Master
Gardener
Your vegetable patch is probably in full swing
right now, yielding an abundance of delicious vegetables for your household. In addition, you may e feeding a hungry horde
of caterpillars, the larvae of moths or butterflies. Some of the suspects that typically plague
vegetable plants during summer include cabbage loopers, tomato hornworms, corn
earworms, and cutworms.
Cabbage loopers are pale green caterpillars that have light stripes running
down their backs. They get their name
from the looped-looking way their bodies appear while moving. They are the larvae brown and gray moths with
silver spots on their upper wings and wingspans of 1 1/2 inches. Cabbage loopers feed on collards, kale,
lettuce, peas, potatoes, radishes, tomatoes and turnips. They can be found most any time during the
growing season.
Tomato hornworms have a distinctive horn or thorn at the rear end. Mature caterpillars can get very large - up
to 4 inches. Their striping pattern
makes them hard to spot despite their size.
They consume entire leaves and small stems, and may chew large pieces
from green fruit. Hornworm damage is
obvious when an infestation is moderate to heavy because of the large amount of
defoliation. Large, black droppings on
the ground beneath tomato plants usually indicate the presence of hornworms.
Corn earworms are also called the tomato fruitworm. Larvae vary in color from shades of green, or
red to brown. They have light and dark
stripes running the length of their bodies.
Most abundant in August and September, corn earworms feed on corn as
well as beans, lettuce, potatoes, tomatoes and certain flowers. On corn, the larvae first feed on the silks
and leaves, and then eventually make their way into the kernels at the tip of
the cob. While they feed they produce
copious amounts of frass (insect poop), a sign of infestation. Once mature, the larvae drop from the plant
and pupate in the soil. Adults are green
to brown moths, and are mostly active at night.
Cutworms attack most garden crops by clipping off seedling stems near or just
below soil level. They are inactive
during the day, hiding under clods of soil until nightfall when they emerge to
feed. The larvae are dull-brownish
caterpillars and may be up to two inches long.
They tend to curl up into a C-shape when disturbed.
Here are some non-chemical strategies to help keep your garden crops from
becoming caterpillar food:
·
Keep your garden plants as vigorous as possible. Healthy, rapidly growing plants often
'outgrow' caterpillar damage. Use plant
varieties recommended for your region, maintain fertile soil and provide enough
moisture to give your crops a way to outgrow pest damage.
·
Time your plantings - corn earworm are less numerous early in the
season. An early planting of vegetables
will often 'escape' with little to no damage.
·
Monitor your garden regularly for signs of caterpillar damage. Remove and dispose of caterpillars that you
find on plants. Hunt cutworms at night
using a flashlight to help detect them.
·
Cover plants with barriers, such as spun fiber row covers to
protect crops from caterpillars but allow light and water to enter. Paper collars placed around the stem collar
of young transplants will help stave off hungry cutworms.
·
Manage your garden for natural predators of caterpillars. For example, lady beetles and spiders feed on
insect eggs, larvae and adults. Parasitic
wasps control caterpillars. The best way
to encourage natural predators of caterpillars is to maintain a diverse and
healthy garden. Avoid broad-spectrum
pesticide applications, as they eliminate both 'bad' pests and 'good' natural
predators.
If a combination of these methods isn't making a
dent in your caterpillar population, try using a microbial pesticide called
Bacillus thuringiensis (BT). This
product is available at most garden stores and is one of the least toxic
materials for caterpillar control. BT is
very effective at killing caterpillars and poses little impact on non-target organisms,
the environment, or human health. Use
according to package instructions and re-apply at intervals as it breaks down
quickly.