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How to Manage Pests
UC Pest Management Guidelines
Cotton
Tobacco Budworm
Scientific Name: Heliothis virescens
(Reviewed 1/08,
updated 8/09)
In this Guideline:
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The budworm is an important pest of cotton only in the desert
valleys. Budworm moths are about 0.75 inch (19 mm) long, with a wing span of 1 to 1.5 inches
(25–37 mm). Eggs are spherical, flattened, with 10 to 15 perpendicular rows of toothed ribs.
Newly hatched larvae have several rows of dark tubercles along the back, each bearing one or two bristles. Larvae range from olive green
to dark reddish brown in color and can be best distinguished from most other
caterpillars by the tiny spines, visible under a hand lens, that cover most of
the body surface. To distinguish the budworm from
bollworm larvae, they must be at least in the third instar. The budworm has a
toothlike structure on the inner surface of the mandibles that is lacking in
the bollworm, and it has the tiny spines of the skin extending onto the
tubercles on top of the eighth abdominal segment; in the bollworm, these tubercles
lack spines.
Heliothis larvae damage bolls
and squares. Larvae chew holes into the base of bolls and may hollow out locks.
Moist frass usually accumulates around the base of the boll. Larvae may also
chew shallow gouges in the boll surface, which can become infected with rot
organisms. Bracts of young squares flare outward and the squares become yellow
and abort from the plant. Older squares may remain but usually have a round
hole and frass near the base. Fifth-instar larvae are the most destructive;
they not only damage more fruit than do earlier instars, but they damage larger
fruit that are harder for the plant to replace.
The impact of a budworm infestation depends on the number of larvae
present, the age of the larvae, and the timing of damage relative to the crop's
fruiting cycle. Although large larvae do most of the damage, it is not possible
to kill a significant proportion of them once they are older than the third
instar. Monitoring and control must therefore be aimed at the eggs and small
larvae.
Natural enemies are very important in managing populations of
budworms. Damaging populations usually do not appear until late in the season,
after treatments for other pests have disrupted natural controls. Insecticides
are needed only if the population exceeds the treatment threshold while the
crop has a significant number of squares or green bolls that will have time to
develop into mature bolls by season's end. There is no need to treat once bolls
begin cracking, because most bolls are too mature by that time to be
susceptible and squares still present will not have time to mature. In the low
desert valleys, there are two periods when injury can occur—one in each
fruiting cycle.
Biological Control
Many predators and parasites combine to substantially maintain Heliothis populations at low levels. Insecticide sprays for
other pests will disrupt this natural control.
Cultural Control
Heliothis are attracted to
succulent, rank-growing cotton plants; keep water, fertilizer, and plant density
at recommended levels to avoid rank growth. Because populations seldom reach
damaging levels before late summer, manage the crop for early maturing and plan
to defoliate by late September.
The use of Bt cotton will help prevent damage by this pest. A
recently developed transgenic cotton, Bollguard II, offers suppression of
cotton bollworm, along with beet armyworms, pink bollworm, and tobacco budworm.
Organically Acceptable Methods
Biological controls, cultural practices that promote early harvest, and
sprays of Bacillus thuringiensis are acceptable
for use on organically grown cotton.
Monitoring and Treatment Decisions
In desert valleys, start sampling in mid-July, about 1 to 2 weeks
after peak squaring. Continue sampling until most bolls have matured. In crops
with a second fruiting cycle, continue until top crop bolls have matured. For
standard sampling, check for larvae on the terminal growth of at least 100
plants chosen at random. Divide fields of up to 80 acres into quarters and
check 25 plants in each quarter. Divide larger fields into more areas and check
25 plants in each area. The treatment threshold is 10 to 12 small budworm or
bollworm larvae per 100 plants. In fields that have been treated previously,
treat when you find 8 small bollworms per 100 plants. Later instar larvae are
the most destructive but are very resistant to insecticides; therefore, aim
treatments at first or second instars.
See UC/ANR Publication 3305, Integrated
Pest Management for Cotton, 2nd edition, for
detailed sampling information, including a sequential sampling program.
| 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, selectivity, persistence,
and impact on 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 ssp. KURSTAKI# |
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(various products) |
Label rates |
4 |
0 |
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SELECTIVITY: High |
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PERSISTENCE: Pest–Short; Natural Enemies–Short |
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MODE OF ACTION GROUP NUMBER1: 11.B2 |
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COMMENTS: Not harmful to beneficials. |
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| B. |
FLUBENDIAMIDE |
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(Belt) SC |
2–3 oz |
12 |
28 |
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SELECTIVITY: High |
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PERSISTENCE: unknown |
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MODE OF ACTION GROUP NUMBER1: 28 |
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COMMENTS: A newer material; impact on beneficials not yet determined. Highly toxic to honey bees. |
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| C. |
ESFENVALERATE* |
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(Asana XL) 0.66EC |
5.8–9.6 fl oz |
12 |
21 |
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SELECTIVITY: Low |
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PERSISTENCE: Pest–Long; Natural Enemies–Moderate |
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MODE OF ACTION GROUP NUMBER1: 3 |
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COMMENTS: Do not graze or feed trash to livestock. Very
destructive to natural enemies; can result in buildup of spider mites and is not recommended in San Joaquin Valley. Do not exceed 0.5 lb a.i./acre/season. |
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| D. |
PROPHENOFOS* |
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(Curacron) 8E |
0.5–1 pt |
72 |
14 |
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SELECTIVITY: Moderate |
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PERSISTENCE: Pest–Moderate; Natural Enemies–Short |
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MODE OF ACTION GROUP NUMBER1: 1B |
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COMMENTS: Use low rate for light to moderate infestations, and high rate for heavy infestations. |
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UC IPM Pest Management Guidelines: Cotton
UC ANR Publication 3444
Insects and Mites
L. D. Godfrey, Entomology, UC Davis
P. B. Goodell, UC IPM Program/ Kearney Agricultural Center, Parlier
E. T. Natwick, UC Cooperative Extension, Imperial County
D. R. Haviland, UC IPM Program, Kern County
Acknowledgment for contributions to Insects and Mites:
E. E. Grafton-Cardwell, Kearney Agricultural Center, Parlier
N. C. Toscano, Entomology, UC Riverside
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