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 leaves webbed together for about two 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 leaffolder 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 before bloom or have been a problem in the past and no parasitism was observed in the previous season, 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 (example 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 leaffolder damage to assess your management program and prepare for next year.
|Common name||Amount per acre**||REI‡||PHI‡|
|(Example trade name)||(hours)||(days)|
|Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least harmful to natural enemies, honey bees, and the environment are at the top of the table. When choosing a pesticide, consider information relating to air and water quality, resistance management, and the pesticide's properties and application timing. Always read the label of the product being used.|
|(Prokil Cryolite 96)||6–8 lb||12||30|
|MODE-OF-ACTION GROUP NUMBER1: 8C|
|COMMENTS: Wine, table, and raisin: two applications maximum. Ground application only. If used on wine grapes or grapes that may be sold to a winery for export, observe their application restrictions. Cryolite is a stomach poison that must be ingested by the leaffolder to be effective so good coverage is essential. The best application timing is before leaf rolling begins. Do not apply more than 20 lb/acre per year.|
|(Intrepid 2F)||10–16 fl oz||4||30|
|MODE-OF-ACTION GROUP NUMBER1: 18|
|COMMENTS: An insect growth regulator that affects lepidopterous larvae only. Must be ingested; most effective when applied to young caterpillars.|
|MODE-OF-ACTION GROUP NUMBER1: 28|
|(Success)||4–8 fl oz||4||7|
|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 honey bees, apply only during late evening, night, or early morning when bees are not present. Do not spray directly nor allow drift onto blooming crops or weeds where bees are foraging.|
|(Delegate WG)||3–5 fl oz||4||7|
|MODE-OF-ACTION GROUP NUMBER1: 5|
|COMMENTS: A stomach poison; most effective when ingested. To protect honey bees, apply only during late evening, night, or early morning when bees are not present. Do not spray directly nor allow drift onto blooming crops or weeds where bees are foraging.|
|F.||BACILLUS THURINGIENSIS ssp. KURSTAKI#|
|(various products)||Label rates||4||0|
|MODE-OF-ACTION GROUP NUMBER1: 11A|
|COMMENTS: Only effective against young larvae. A stomach poison that must be ingested by the leaffolder to be effective. Good coverage is essential. Has a short residual so is most effective when applied 3 or 4 days before leaf rolling by the main brood.|
|**||Apply with enough water to provide complete coverage.|
|‡||Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI The longer of two intervals is the minimum time that must elapse before harvest.|
|*||Permit required from county agricultural commissioner for purchase or use.|
|#||Acceptable for use on organically grown produce.|
|1||Rotate chemicals with a different mode-of-action Group number, and do not use products with the same mode-of-action Group number more than twice per season to help prevent the development of resistance. For example, the organo-phosphates have a Group number of 1B; chemicals with a 1B Group number should be alternated with chemicals that have a Group number other than 1B. Mode-of-action group numbers ("un"=unknown or uncertain mode of action) are assigned by IRAC (Insecticide Resistance Action Committee).|