How to Manage Pests

UC Pest Management Guidelines

DESCRIPTION OF THE PEST

The adult omnivorous leafroller is bell-shaped with blackish gray snouthlike mouthparts that protrude forward from the head. Forewings are dark rusty brown with the tip being tan in color. Size varies from 0.38 to 0.5 inch long. Omnivorous leafroller overwinters in the larval stage in grape mummies, vineyard weeds, and other trash in the vineyard. In spring, larvae complete their development and moths emerge and lay shinglelike egg masses on grape leaves. After about 5 days these eggs hatch, and larvae web two young leaves together to form a nest in which they feed. It does not roll leaves as does the grape leaffolder; instead, it ties leaves together and feeds inside. Later, nests can be found in flower clusters (May) and bunches (June-Sept.), as well as on leaves and in shoot tips.

Omnivorous leafroller larvae are often confused with grape leaffolders. Omnivorous leafrollers can have either a black or brown head capsule, depending on the instar. Mature larvae range in color from cream to brownish green with whitish slightly convex tubercles on the top of the abdomen. The grape leaffolder does not have whitish tubercles. In addition omnivorous leafroller larvae usually drop to the ground on a thread when disturbed, rather than dropping directly, as is the case with the grape leaffolder.

Generally, there are four flight periods each year with a partial fifth in warmer years. Adult flights generally occur in spring (Feb-April), late May, mid-July, and late August or early September. The first of five larval instars appears a short time after a flight starts.

DAMAGE

The omnivorous leafroller can cause serious damage in California's Central Valley and inner coastal vineyards. Although it does feed on leaves, flowers, and developing berries, the most significant damage occurs after veraision when feeding allows rot organisms to enter fruit at the damage sites.

MANAGEMENT

Populations are usually small in spring and early summer but may increase greatly later in summer and cause severe berry rot problems. The increase may be a result of migration triggered by the drying out of weed plant hosts. Consequently, cultural control is an important component in managing this pest. Spring treatments are recommended if the vineyard has a history of problems with this pest. Otherwise chemical treatments are necessary only when monitoring indicates a need.

Biological Control
More than 10 species of parasites have been recorded from omnivorous leafroller. However, seldom does mortality from these parasites exceed 10%. Predators such as lacewings, minute pirate bugs and spiders have also been found to feed on omnivorous leafroller larvae.

Cultural Control
During the dormant season remove mummy clusters and control vineyard weeds. French plow and disc clusters and weeds to bury overwintering larvae living on weeds in ground duff and dried berries. During dormancy, prune out old fruit mummies and destroy by flailing or shredding. Early harvest can also prevent infestation by fourth generation larvae. Removing basal leaves will also improve coverage and efficacy of cryolite, Bacillus thuringiensis, and other pesticides. In warmer growing areas, be careful not to remove excessive numbers of leaves, which can lead to sunburned fruit.

Organically Acceptable Methods
Cultural and biological controls and sprays of Bacillus thuringiensis and the Entrust formulation of spinosad are acceptable on organically certified grapes.

Monitoring and Treatment Decisions   Degree-day calculator    Degree-day table
Treat for omnivorous leafroller at bloom if the vineyard has a history of this pest or if a serious infestation occurred in the previous season.Otherwise, monitor to determine the need for treatment. Monitor along with other caterpillars as outlined in MONITORING CATERPILLARS; record results on a monitoring form (100KB, PDF).

Acceptable damage levels at harvest are about 1-2% for raisin grapes and less for wine and table grape varieties. Trying to reduce damage any further than this threshold would probably not be cost effective.

Thorough coverage with spray applications is extremely important to protect the berries. Such coverage is difficult in tight bunches so make a major effort to control this pest before bunch closing. Improved coverage and efficacy of pesticides can be obtained by removing basal leaves (see CULTURAL CONTROL). In Central Valley and other warm inland valley vineyards, use pheromone traps, degree-days, and monitoring to assess omnivorous leafroller populations.

Pheromone traps. Place pheromone traps in the vineyard just before budbreak, and check traps twice a week. Information obtained from trap catches is used to establish a biofix, which is an identifiable point in the life cycle of this pest. For omnivorous leafroller, the biofix is the first night moths are consistently caught in traps. Continue to monitor with pheromone traps through fruit set, until berries are pea-sized, to track adult flights of subsequent generations. For information on placing and monitoring traps in a vineyard, see PHEROMONE TRAPS.

Degree-days. Once biofix is reached, begin accumulating degree-days from the biofix using a lower threshold of 48°F and an upper threshold of 87°F. (For assistance in calculating degree-days, see "Degree-days"). When 500 degree-days have accumulated, egg hatch starts, and it is time to sample clusters.

Monitoring. At bloom, monitor 200 flower clusters (10 clusters in the middle of 20 vines) to determine if omnivorous leafroller is present. If you find any omnivorous leafrollers or damage, treat.

Following bloom, if there is a cover-crop or abundant weeds, use a sweep-net to sample for larvae or thoroughly inspect the weeds. If larvae are found in the weeds but not in the grape clusters, start sampling clusters intensively for second generation larvae at 300 degree-days after the 2nd flight biofix (minimum of once a week and 200 clusters). Treatments are warranted if more than 1% of the clusters have omnivorous leafroller larvae or nests. Because of the additional foliage at this time (late June-early July), apply second generation treatments at a slow speed (max. 3 mph) to achieve adequate coverage of the clusters.

If surrounding crops are producing omnivorous leafroller moths, a 3rd generation treatment might be necessary.

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PUBLICATION

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 the insects and mites section:
J. Granett, Entomology, UC Davis

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