How to Manage Pests
UC Pest Management Guidelines
Tomato
Hornworms
Scientific names: Tobacco hornworm: Manduca sexta
Tomato hornworm: Manduca quinquemaculata
(Reviewed 1/08,
updated 1/08)
In this Guideline:
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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 areas.
Hornworms feed on blossoms, leaves, and fruit. At high
populations they can extensively defoliate plants and scar the fruit. They are
rarely a problem in the warmer interior valleys unless natural enemies are
disrupted, in which case, they can do serious damage. They are mostly problems in garden situations.
In commercial tomato
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.
Biological Control
There are several important naturally occurring parasites that help control
hornworms in tomatoes. Hornworm eggs are attacked by Trichogramma parasites and the
larvae by Hyposoter exiguae.
Trichogramma released for control of tomato
fruitworm will also attack hornworm eggs.
Cultural Control
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.
Organically Acceptable
Methods
Biological and cultural controls as well as Bacillus thuringiensis sprays are acceptable for use on an organically certified crop.
Monitoring
and Treatment Decisions
Treat hornworms only if they are causing extensive foliage damage, or if they
are feeding on fruit. Hornworm
damage can be assessed as part of the sampling guidelines and thresholds listed
under beet armyworm. 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. In addition, hornworm feeding produces larger,
deeper cavities than those caused by beet armyworm. Consider spot-treating
sections of a field where hornworm damage is found because it is rare for an
entire field to become infested.
| Common name |
Amount/Acre** |
R.E.I.+ |
P.H.I.+ |
| (trade name) |
|
(hours) |
(days) |
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| 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.
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| A. |
BACILLUS THURINGIENSIS spp. KURSTAKI# |
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(various products) |
Label rates |
4 |
0 |
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MODE
OF ACTION GROUP NUMBER1: 11.B2
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COMMENTS:
This material is highly effective against hornworms and does not destroy the
natural enemies of tomato pests. It will also control loopers and to some extent beet armyworms and tomato fruitworms. |
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| B. |
ESFENVALERATE*^ |
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(Asana XL) 0.66 EC |
2.9–5.8 fl oz |
12 |
1 |
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MODE
OF ACTION GROUP NUMBER1: 3
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COMMENTS:
Do not exceed 0.5 lb a.i./acre/season. Do not use this product if leafminers are present because it is destructive of their parasites. |
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| C. |
CARBARYL*^ |
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(Sevin) 80S |
1.5–2.5 lb |
12 |
3 |
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(XLR Plus) |
1–2 qt |
12 |
3 |
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MODE
OF ACTION GROUP NUMBER1: 1A
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COMMENTS:
Do not use if psyllids are in the field as carbamates tend to promote development of their populations. |
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UC IPM Pest Management Guidelines: Tomato
UC ANR Publication 3470
Insects and Mites
F. G. Zalom, Entomology, UC Davis
J. T. Trumble, Entomology, UC Riverside
C. F. Fouche, UC Cooperative Extension, San Joaquin Co.
C. G. Summers, Entomology, UC Davis/Kearney Agricultural Center, Parlier
Acknowledgments for contributions to the insects and mites section:
N. C. Toscano, Entomology, UC Riverside
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