How to Manage Pests
UC Pest Management Guidelines
Scientific name: Desmia funeralis
(Reviewed 6/06, updated 4/14)
In this Guideline:
Description of the Pest
Moths of the grape leaffolder are almost black, with two white spots on the forewings and two white stripes across the abdomen. Larvae are translucent but appear greenish because ingested leaf tissue shows through the body wall. Small black spots, located above the second pair of legs, are present on later instar larvae. This helps distinguish them from omnivorous leafroller.
Grape leaffolders have three generations a year (about April-May, June 15-July 15, and August). After overwintering as pupae, moths emerge in April or May and lay flat, elliptical eggs singly on either the upper or lower surface of the leaf. Many are deposited against the leaf veins on the underside of the leaf. After hatching, larvae feed between two webbed leaves for about 2 weeks. Then each pale green, translucent larva rolls a leaf edge and feeds from the inside on the leaf edge. Larvae turn darker green as a result of this leaf feeding. If disturbed, larvae wriggle vigorously and drop to the ground without a silken thread. Mature larvae construct a separate leaf envelope on the edge of a leaf in which they pupate.
Grape leafroller can reduce leaf surface by constructing leaf rolls and by leaf feeding. Twenty percent leaf reduction can be tolerated 1 month after fruit set in the San Joaquin Valley. Even more leaf damage can be tolerated later. However, third generation damage can be severe enough to cause complete defoliation, which leads to sunburned berries, soft fruit, and direct berry feeding by leaffolder larvae.
Parasites play an important role in keeping grape leaffolder below a level that will cause damage. There seems to be no correlation between the past season's population and the current season's first generation nor with the population density that may develop later. Treatment of the first generation is rarely needed. However, inspect and judge each brood as to its potential to cause economic damage.
Several parasites attack grape leaffolder. Among the most common is the larval parasite Bracon cushmani. After stinging and paralyzing leaffolder larvae, female B. cushmani lay from one to several eggs on the body of leaffolder larvae. Bracon cushmani larvae feed externally and, after completing their development, pupate next to the consumed host. Parasitism by this parasite frequently reduces second and third generation populations to below economic levels. In addition to B. cushmani, several other hymenopteran parasites and at least two species of flies parasitize leaffolder. Generalist predators such as lacewings and spiders also attack grape leaffolder larvae.
Organically Acceptable Methods
Biological control and sprays of Bacillus thuringiensis and the Entrust formulation of spinosad are organically acceptable methods.
Monitoring and Treatment Decisions
Grape leaffolder can be monitored along with other pests following the procedures in MONITORING CATERPILLARS. If grape leaffolders are present in the vineyard or have been a problem in the past, plan to treat at bloom. Otherwise, monitor for the characteristic group feeding of young larvae between leaves. As larvae begin making rolls, examine the vineyard every 2 to 3 days to detect a greater than expected increase. Record results on a monitoring form .
Unroll leaves to check for parasitism. Populations tend to be spotty, and defoliation of a few vines used for raisin or wine grapes can probably be tolerated; however, table grapes should probably be treated. If treatment is warranted, treat as soon as a few rolls are noticed from the generation being treated because small larvae are more easily killed than older instars. Usually treatments applied for grapeleaf skeletonizer and omnivorous leafroller will also control grape leaffolder.
At harvest, check table grapes for grape leafroller damage to assess your management program and prepare for next year.
UC IPM Pest Management Guidelines: Grape
Insects and Mites
W. J. Bentley, UC IPM Program, Kearney Agricultural Research Center, Parlier
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