How to Manage Pests
UC Pest Management Guidelines
Alfalfa
Variegated
and Other Cutworms
Scientific Names:
Granulate cutworm: Agrotis subterranea
Variegated cutworm: Peridroma saucia
(Reviewed 11/06,
updated 11/06)
In this Guideline:
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Cutworms are only occasional pests of high desert and Central Valley
alfalfa but are frequent pests in the low desert where alfalfa is planted on
beds. The granulate and the variegated cutworms are the two species that most
commonly attack low desert alfalfa.
Female moths lay white or greenish eggs in irregular masses on
leaves or stems of plants, often near the base of the plant. Eggs darken as
they approach hatching. Full grown
caterpillars are
about 1.5 to 2 inches long and appear as smooth-skinned caterpillars of various
colors and patterns. Larvae frequently roll into a C-shape when disturbed.
Cutworms feed at night and hide during the day in soil cracks and under debris
and loose soil.
In the Central Valley, variegated cutworm populations may develop in
weedy areas and migrate into seedling stands or occasionally mature stands.
Injurious populations usually occur from April to late June. Seedling alfalfa
stands can be severely damaged by cutworms cutting the seedlings off at or just
below the soil surface.
Established fields are damaged when cutworms cut off new growth or feed
on the alfalfa foliage.
Granulate cutworm is a devastating pest of bed-planted alfalfa
and can also be a pest of alfalfa planted between borders. Low desert alfalfa
fields are attacked from May through October, but the pest occurs year round in
fields. Established alfalfa fields can be severely injured when cutworms cut
off new shoots at or below ground level following harvest. The pest often goes
undetected after cutting and hay removal but the problem becomes apparent when
the field is irrigated and there is little or no regrowth.
Tillage, flood irrigation, and weed control are important in cutworm
management. When damage is severe in seedling fields, apply an insecticide
bait.
Cultural Control
Tillage helps to limit cutworm populations; seedlings in well-tilled
fields—especially when there is an interval between crops—are less likely to
have cutworm problems. Keep the field and field edges weed-free. Flood
irrigation can drown many cutworm larvae. Flood irrigation during the day will
attract many birds that prey on the cutworms as the advancing water forces
larvae from hiding.
Organically Acceptable Methods
Cultural controls are acceptable for use on an organically certified
crop.
Monitoring and Treatment Decisions
Cutworm infestations are sporadic, and treatment guidelines have not
been established in California. Check for cutworms by looking under duff and
carefully digging to a depth of 1 inch in loose soil near alfalfa crowns. When
cutworm numbers exceed one or two per foot of row or severe damage is apparent,
it may be necessary to treat. If treating with baits, apply baits in late
evening or at night when cutworms are on plants.
| 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, taking into account efficacy and impact on natural enemies and
honey bees. When choosing a
pesticide, also consider environmental impact.
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| A. |
PERMETHRIN* |
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(Pounce) 25WP, 3.2EC, WSB |
Label rates |
12 |
14 |
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(Ambush) 25WP |
8.2–12.8 oz |
12 |
14 |
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MODE
OF ACTION: A pyrethroid (Group 3)1 insecticide.
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| B. |
CYFLUTHRIN* |
| |
(Baythroid) 2E |
0.8–1.6 fl oz |
12 |
7 |
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(Renounce) 20WP |
1–2 oz |
12 |
7 |
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MODE OF ACTION: A pyrethroid (Group 3)1
insecticide.
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| C. |
LAMBDA-CYHALOTHRIN* |
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(Warrior) |
1.92–3.2 fl oz |
24 |
7 – hay; 1 – forage |
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MODE OF ACTION: A pyrethroid (Group 3)1
insecticide.
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COMMENTS: Do not apply when bees are actively foraging. Do not apply more than 0.24 pt/acre/cutting or 0.96 pt/acre/season. |
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| D. |
INDOXACARB |
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(Steward) 1.25 SC |
6.7–11.3 fl oz |
12 |
7 |
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MODE OF ACTION: An oxadiazine (Group 22)1
insecticide.
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COMMENTS: Make no more than one application per cutting. Not
for use in alfalfa grown for seed or for sprouts for human consumption. Do not apply more than 45 fl oz/acre/crop season. |
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UC IPM Pest Management Guidelines: Alfalfa
UC ANR Publication 3430
Insects and Mites
C. G. Summers, Entomology, Kearney Agricultural Center, Parlier
L. D. Godfrey, Entomology, UC Davis
M. Rethwisch, UC Cooperative Extension, Riverside County (Blythe)
D. R. Haviland, UC Cooperative Extension, Kern County
P. B. Goodell, Entomology, Kearney Agricultural Center, Parlier
R. F. Long, UC Cooperative Extension, Yolo County
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