How to Manage Pests
UC Pest Management Guidelines
Scientific Names: Tobacco
hornworm: Manduca sexta
Tomato hornworm: Manduca quinquemaculata
In this Guideline:
Hornworm eggs are laid singly on leaves. While both
species of hornworms have a large horn on the posterior end of the body, the
tobacco hornworm has seven diagonal stripes on each side of the body in
contrast to the tomato hornworm, which has eight chevron-shaped stripes. Larvae
feed for 3 or 4 weeks, then burrow into the soil to pupate. The adult moth is a strong flier with a wingspan up to 5
inches (12 cm). Development takes about 2 months in summer; the winter is
passed in the pupal stage. There are two generations a year in most areas;
larvae are usually most common in midsummer, but there may be a small
population peak in late summer. Infestations tend to be more severe in warm inland
Hornworms feed primarily on leaves but will eat blossoms and stems when the
leaves are gone and even burrow into fruit. At high populations they can
extensively defoliate plants and scar the fruit. Infestations tend to be
spotty, and if left unchecked can cause considerable damage.
In commercial fields, natural enemies, crop rotation, and discing
after harvest play a key role in keeping hornworm populations below damaging
levels. Conserve natural enemies by not treating with disruptive pesticides,
especially early in the season before fruit begin to mature.
There are several important naturally occurring parasites that help control
hornworms in eggplants. Hornworm eggs are attacked by Trichogramma
parasites and the larvae by Hyposoter exiguae.
Discing after harvest destroys pupae in the soil. Rotations with crops that are
not attacked by hornworms will also help to keep population levels low in
individual fields. In small fields, handpicking hornworms off plants is
effective but as in tomatoes, it can be difficult to find the worms, which are
camouflaged by the foliage.
Organically Acceptable Methods
Biological and cultural controls as well as sprays of Bacillus thuringiensis or the Entrust formulation of spinosad are
acceptable for use on an organically certified crop.
and Treatment Decisions
It is rare for an entire field to become infested. Consider spot-treating
sections of a field where hornworm damage is found. It is not uncommon to find
various locations in a 20-acre field, each with 10-40 plants being stripped of
leaves. Look for hornworm larvae on plants that have severe foliar damage as
you sample to determine if damage is the result of hornworm or armyworm
activity. On fruit, hornworm feeding produces larger, deeper cavities than
those caused by beet armyworm.
|The following materials are listed in order of usefulness in an IPM
program, taking into account efficacy and impact on natural enemies
and honey bees. When choosing a pesticide, also consider
information relating to environmental impact. Not all registered pesticides
are listed. Always read label of product being used.
||BACILLUS THURINGIENSIS spp. KURSTAKI#
||MODE OF ACTION GROUP NUMBER1: 11
||COMMENTS: This material is highly effective against hornworms;
especially when applied early to young caterpillars. It will also control loopers and to some extent beet armyworms.
||MODE OF ACTION GROUP NUMBER1: 5
||COMMENTS: Use higher rate for larger worms and heavy
infestations. Best control is achieved when aimed at newly hatched larvae and
coverage is thorough. More broad-spectrum than Bt but has very low toxicity
to humans, vertebrates, and the adults of many natural enemies. Can remain
toxic to larval stages (especially syrphid fly) for 5-7 days after treatment. Do not exceed 29 fl oz of Success or 9 oz of Entrust/acre/crop.
UC IPM Pest Management Guidelines: Eggplant
UC ANR Publication 3475
Insects and Mites
R. H. Molinar, UC Cooperative Extension Fresno County
J. L. Aguiar, UC Cooperative Extension Riverside County
M. J. Jimenez, UC Cooperative Extension Tulare County
P. B. Goodell, UC IPM, Kearney Agricultural Center, Parlier
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