How to Manage Pests
UC Pest Management Guidelines
Variegated cutworm: Peridroma saucia
Spotted cutworm: Xestia (Amathes) c-nigrum
Brassy cutworm: Orthodes rufula and other species
In this Guideline:
Cutworms are inconspicously marked, dull-colored caterpillars
ranging from 0.6 to 2.0 inch (1.5–5 cm) in length. Positive
identification is important as behavioral differences affect control actions.
cutworm larvae are 1.5 to 2.0 inch
(3.8–5 cm) long with smooth skin. Body color varies from pale gray to
dark mottled brown intermixed with red and yellow dots along the dorsum.
Mature spotted cutworms are about 1.3 inch (3.5 cm) long and are a dull
gray brown. A row of dark or black triangular markings are found on each side
of the dorsal body surface.
Mature brassy cutworms are 1.0 to 1.2 inch (2.5–3 cm) long and are
reddish or brassy in appearance. Of the cutworm species that attack grapes,
brassy cutworm is the only one with hairs protruding from the compound eye
area. A hand lens is needed to detect these hairs.
Variegated cutworm is the predominant species in the San Joaquin
Valley and North Coast, while spotted cutworm is predominant in the Central
Coast counties. In the North Coast, the variegated cutworm normally returns to
the ground during the day but may also remain under the bark of the vine. In
the San Joaquin Valley variegated cutworm larvae do not return to the soil but
rather move under the bark.
Spotted cutworms routinely remain under grapevine bark in all production areas.
Feeding on grapevines occurs from bud swell to when shoots are
several inches long. Injured buds may fail to develop. Grapevines can compensate for early season damage to buds
or shoots to some extent by the growth of secondary buds. The fruitfulness of
secondary buds, however, varies according to variety, and some varieties such
as Thompson Seedless and Chardonnay have unfruitful or significantly less
fruitful secondary buds respectively. In these varieties, destruction of
primary buds can be expected to reduce the number of clusters in proportion to
the number of buds destroyed.
Historical records of cutworm infestations or damage are useful in
developing monitoring strategies for individual vineyards because cutworm
problems are normally spotty or localized. Many varieties of grapes can
tolerate a significant amount of damage without any economic loss. No chemicals
are highly effective in controlling cutworms, so frequently treatments may not
be economically justified.
enemies of cutworms include predaceous or parasitic insects, mammals, parasitic
nematodes, pathogens, birds, and reptiles. The hymenopteran (wasp) parasites,
including ichneumonids, chalcids, braconids, and sphecids, are the most
important group of cutworm natural enemies. Predaceous beetles (often found
under bark) and tachinid flies are also factors in biological control.
practices have not been demonstrated to successfully control cutworms; however,
some practices do affect their population abundance. Weed removal in late
summer or fall may be beneficial in disrupting cutworm life cycles. Plowing or
discing of weeds is not recommended before or soon after bud swell in spring
where cutworms are a problem because it can cause movement of cutworms to the
grapevines. Furrow and flood irrigation can be manipulated to bring cutworm
larvae to the soil surface, exposing them to adverse weather and predators.
Organically Acceptable Methods
cultural controls and the Entrust formulation of spinosad are organically
Monitoring and Treatment
monitor bud feeding by cutworms during bud swell in early spring. Cutworms can
be monitored along with other pests following the procedures discussed in
DELAYED-DORMANT AND BUDBREAK MONITORING (wine/raisin grapes or table grapes). Because cutworm
infestations are clumped, many vines must be examined to detect an infestation.
In spring cutworms leave the soil and climb up the vines. During the day they
hid under loose bark towards the base of the vine and come out to feed at
night. Randomly select five locations in the vineyard to observe, concentrating
on areas known to be chronically infested. Check 4 vines within each location
for damaged buds (total 20 vines). On each vine examine 5 buds for damage
(total 25 buds per location).
In cool growing regions with a long period
between bud swell and shoot growth, monitoring may be needed over a 2- to
3-week period. Record results on a monitoring form (example
The number of damaged buds that can be tolerated depends on
variety. If secondary buds are highly fruitful, little yield loss will result
even when a large proportion of buds are damaged. If less than 4% of the buds
are damaged, treatment may be unnecessary. Treating an entire vineyard is
seldom necessary because infestations are usually localized; consider spot
treatments. Cutworm feeding after shoots are about 6 inches long does not
result in significant injury.
To make sure cutworms are causing the damage, return to damaged
vines at night to look for cutworm larvae. Other species of insects (grape bud beetle, click
beetles, branch and twig borers, orange tortix larvae) also cause similar
|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.
||MODE OF ACTION GROUP NUMBER1: 1A
||COMMENTS: Disruptive to predators of mites
and parasites of leafhoppers; do not use where mites are a chronic problem. Extremely toxic to honey bees.
||MODE OF ACTION GROUP NUMBER1: 1A
||COMMENTS: Do not feed treated grapes to
livestock. Disruptive to predators of mites and parasites of leafhopper. Very toxic to honey bees.
||MODE OF ACTION GROUP NUMBER1: 5
||COMMENTS: Apply when eggs first hatch to
target the young larvae. A stomach poison; most effective when ingested.
Heavy infestations require a second application in 4 or 5 days. To protect
honeybees, apply only during late evening, night, and early morning when bees are not present in the vineyard.
||MODE OF ACTION GROUP NUMBER1: 1B
||COMMENTS: Apply in May in a minimum of 100
gal water and a maximum of 200 gal water/acre. Very toxic to honey bees. Avoid drift and tailwater runoff into surface waters.
UC IPM Pest Management Guidelines: Grape
UC ANR Publication 3448
Insects and Mites
W. J. Bentley, UC IPM Program, Kearney Agricultural Research Center, Parlier
L. G. Varela, UC IPM Program, Sonoma County
F. G. Zalom, Entomology, UC Davis
R. J. Smith, UC Cooperative Extension, Sonoma County
A. H. Purcell, Environmental Science, Policy and Management, UC Berkeley
P. A. Phillips, UC IPM Program, Ventura County
D. R. Haviland, UC IPM Program, Kern County
K. M. Daane, Kearney Agricultural Research Center, Parlier
M. C. Battany, UC Cooperative Extension, San Luis Obispo County
Acknowledgment for contributions to Insects and Mites:
J. Granett, Entomology, UC Davis
Top of page