Managing Leafhoppers in Wine Grapes
Identification and management of western and variegated grape leafhoppers, including species differences, monitoring methods, economic thresholds, biological controls, and treatment options.
Leafhopper Species in Wine Grapes
Two leafhopper species are economically significant in western U.S. wine grape production: the western grape leafhopper (Erythroneura elegantula) and the variegated grape leafhopper (Erythroneura variabilis). Both species feed on the undersides of grape leaves by piercing cells and extracting sap, leaving characteristic white stippling marks that reduce photosynthetic capacity when populations are high enough. Both species also produce copious frass deposits that can contaminate fruit.
Distinguishing the two species matters for management because they have slightly different phenology and their biological control situations differ. Western grape leafhopper has one reliable biocontrol agent; variegated grape leafhopper is harder to control biologically and more likely to require intervention in high-pressure years.
Species Identification
Western grape leafhopper adults are yellow-white with red and brown markings on the wings, approximately 3mm long. The pattern consists of diagonal bands on the forewing. Nymphs are nearly white to pale yellow.
Variegated grape leafhopper adults are similar in size but have more complex patterning, with a mosaic of brown, cream, and reddish markings that give them a variegated appearance compared to the cleaner banding of western grape leafhopper. Nymphs are similar in appearance to western grape leafhopper nymphs; species determination in the nymph stage often requires examination of the abdominal chaetotaxy pattern under magnification.
In practice, mixed populations occur throughout California's wine grape regions, and management thresholds and decisions are often made based on combined populations rather than species-specific counts.
Monitoring Methods
Leafhopper populations are monitored by leaf sampling. The standard method is to randomly select 30 to 50 leaves per block, drawn from the middle of the cluster zone from vines distributed throughout the block. Count nymphs on the underside of each leaf. Record the average number of nymphs per leaf and any observations about the distribution of damage across the block.
Sampling should begin in late May or early June when first generation nymphs are active and continue through August for second generation monitoring. Yellow sticky traps can detect adult flight timing but are not effective for population density assessment.
Economic Thresholds
The economic threshold for leafhoppers in wine grapes varies by region and crop value. UC IPM guidelines suggest considering treatment when populations reach 15 to 20 nymphs per leaf for premium wine grapes at risk of frass contamination. Other sources use 3 to 5 nymphs per leaf as a more conservative threshold for blocks where fruit quality or certification standards are priority concerns.
The more practically useful threshold concept in wine grape production is the combination of nymph counts with an assessment of biological control pressure. If Anagrus wasps are active and parasitism rates are high, treatment may be avoidable even at moderate population levels. If biocontrol is absent or low, lower thresholds warrant action.
Biological Control: Anagrus Wasps
Anagrus epos and related parasitic wasps are the primary natural enemies of grape leafhoppers in California. These tiny wasps (under 1mm) parasitize leafhopper eggs, reducing the next generation's population. Anagrus populations are supported by non-crop habitat that provides overwintering sites and alternative hosts, particularly Italian prune trees and blackberries near vineyard edges.
Vineyard practices that support Anagrus include maintaining hedgerows or prune tree borders adjacent to vineyards, avoiding broad-spectrum insecticide applications that kill the wasps alongside their targets, and maintaining cover crops in the midrow that provide habitat and alternative prey.
Tracking Anagrus activity alongside leafhopper monitoring adds meaningful context to population data. When 50% or more of leafhopper eggs are parasitized, populations typically decline without intervention. Below 20% parasitism, biological control is insufficient to prevent buildup.
Treatment Options
When treatment thresholds are reached and biological control is insufficient, options range from selective materials that spare beneficials to conventional insecticides. Kaolin clay (Surround WP) creates a physical barrier that disrupts leafhopper feeding and reduces second generation egg deposition when applied consistently. Insecticidal soaps and pyrethrin products provide knockdown with short residual, minimizing impact on Anagrus.
Conventional options include spirotetramat (Movento, IRAC Group 23), which has systemic activity and relatively lower impact on beneficials than older organophosphate options. Acetamiprid and imidacloprid (neonicotinoids) are effective but carry pollinator risk concerns and are restricted or prohibited in some organic and sustainable certification programs.
Record every treatment by block in VitisScribe with the IRAC group for resistance management tracking, alongside your monitoring data that justified the decision. This documentation is essential for organic certification audits and for building a multi-year picture of leafhopper pressure in each block.