Container Gardening Complete

Job:06-700309 Title: CPS - Container Gardening Complete

700309 - ContainerGardens_001-272_FINAL.indd 192 5/24/17 12:19 PM
Job:06-700309 Title: CPS - Container Gardening Complete
Job:06-700309 Title: CPS - Container Gardening Complete

700309 - ContainerGardens_001-272_FINAL.indd 193 5/24/17 12:19 PM

192 chapter 4

Tomato and Tobacco Hornworms

(Manduca quinquemaculata and

Manduca sexta)

North American geographical range: All

Identification: Hornworms are the large, green

larvae of nocturnal moths commonly called

sphinx or hawk moths. Mature caterpillars can

grow up to 5 in. long. They pupate underground.

Plants affected: Members of the nightshade

family, including tomato, tobacco, potatoes,

peppers, and eggplants.

Feeding habits and damage: Gardeners often

find the dark pellets of excrement left behind

by hornworms before they spot the caterpillars

themselves. Damage in the form of missing leaves

is first noted on the tops of plants where the

caterpillars feed at night. They shelter under or on

interior leaves during the day, often making them

difficult to find.

Physical controls: Hornworms frequently fall prey

to non-stinging parasitic wasps that use them as

hosts for their developing young. The tiny cotesia

wasp inserts eggs under the caterpillar’s skin that

eventually hatch into larval wasps. The larval

wasps consume the inside of the hornworm’s

body and soon emerge through the hornworm’s

skin to spin external cocoons. If you spot a

hornworm with white, rice-like sacks hanging

from its back, don’t disturb it: it’s already stopped

feeding and will soon die. Hornworms are also

easily handpicked from plants.

Product controls: Bacillus thuringiensis (B.t.)

and spinosad work but are seldom necessary.

Handpicking is far more effective when you’re

growing just a few plants.

Tobacco and tomato hornworms measure up to 5

in. long before dropping o their host plant and

burrowing into the ground to pupate.

This tobacco hornworm has been parasitized by the

cotesia wasp. The white, rice-like cocoons hanging o

its back contain the wasp pupae.

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Troubleshooting 193

Whiteflies (Trialeurodes

vaporariorum and several

other species)

North American geographical range: All.

Greenhouse and indoor pests year-round in the

north. Outdoor pests during the summer in

the north. Active year-round in southern regions.

Identification: Adult whiteflies are tiny, white,

moth-like flies that measure only^1 ⁄ 20 to^1 ⁄ 10 in.

Infested plants emit a cloud of flying insects when

disturbed. They exude a sweet excrement called

honeydew that leaves a sticky, shiny film on leaves

and other nearby surfaces. Whitefly larvae are

extremely tiny and do not have wings.

Plants affected: Almost any plant can host

whiteflies, but common hosts include tomatoes,

geraniums, sweet potatoes, citrus trees, bedding

plants, poinsettias, and flowering tobacco.

Feeding habits and damage: Adult and immature

whiteflies both feed by sucking plant juices

from leaf undersides. Outdoor populations

seldom do significant damage, except in the

south. In greenhouses, where populations can

grow to significant levels, whiteflies can be very

problematic. Whitefly feeding weakens plants,

yellows leaves, and causes wilt and leaf drop.

Physical controls: Whiteflies are easily trapped on

yellow sticky cards placed just above plant tops.

Product controls: Insecticidal soap, horticultural

oil, neem, citrus oil, hot pepper wax.

Whiteflies are tiny and very annoying. Severely infested plants emit a cloud of white, flying insects when disturbed.

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