How to Manage Pests
UC Pest Management Guidelines
European Fruit Lecanium Scale
Scientific name: Parthenolecanium corni
In this Guideline:
Description of the Pest
European fruit lecanium is a scale insect that is also known as the brown apricot scale. The adult female's domed shell is shiny brown and about 0.4 inch in diameter. Adult females are mostly found on 1- to 3-year-old wood on the underside of woody canes, cordons, and spurs where they remain for the rest of their lives. Females reproduce parthenogenetically (without mating), and eggs are laid in spring (beginning in April) beneath the female's body. Crawlers hatch from May through most of June. They move to the shoots and leaves of the current season's growth and molt to second instars from June to July.
In the North Coast a portion of the second–instar population continues development and becomes adults that produce a second generation. The crawlers of the second generation may be found on leaf petioles and shoots in August. Beginning in September, second-instar nymphs from both the first and second generation migrate back to 1- to 3-year-old wood. They overwinter under the bark in the second-instar stage. Early in spring, the second instars molt to the third-instar stage and then quickly develop into mature females that begin laying eggs in April and May. There is usually only one generation each year, but a portion of the population in the North Coast will have two generations. The second generation has not been observed in other grape-growing regions.
European fruit lecanium scale produces honeydew as it feeds. Sooty mold may grow on the honeydew, causing blackened areas on leaves and fruit. When European fruit lecanium occurs in abundance, it may stunt vine growth.
Parasites and predators often keep populations below damaging levels. Only when populations increase to great numbers should insecticide applications be considered.
Honeydew-seeking ants must be controlled to allow natural enemies of scale to aid in its control. This is best accomplished either with tillage or by treating the ants with an insecticide. See the section on ANTS for additional information on their control.
European fruit lecanium is attacked by several species of parasites, including Aphytis spp., Coccophagus spp., Encarsia spp., and Metaphycus luteolus. Important parasites in the North Coast region are Metaphycus insidiosus, Coccophagus lycimnia, and Blastothrix longipennis. Frequently, second-instar scales may be heavily parasitized early in spring before budbreak. In addition, many common predators help control this scale. These include lady beetles (Chilocorus orbus, Hyperaspis spp., Rhyzobius lophanthae), lacewings, the predaceous sap beetle (Cybocephalus californicus) and predatory seed bugs (Phytocoris spp.).
Organically Acceptable Methods
Organically acceptable methods of controlling European fruit lecanium include biological control and oil sprays.
Monitoring and Treatment Decisions
Monitor closely throughout the year and make a map of infested areas in the vineyard. Monitor 1- to 3-year-old wood in early March for the presence of parasitism of second-instar scale nymphs. Place the scales in gelatin capsules (available from pharmacies) and hold the capsules at room temperature for 2-4 weeks to detect parasite emergence, or look for round exit holes on the scale bodies. You can also monitor female development on old wood. Monitor for crawler emergence in May by placing double-sided sticky tape around 1-year-old wood near the females, or by turning over the females and looking for crawlers.
The crawler stage is the stage most susceptible to chemical treatment, especially when using summer oil sprays. Crawlers emerge for a period of about 6 weeks, starting in mid-May. Treatment levels for scale have not been established. Determine the need for treatment of European fruit lecanium by evaluating records of honeydew from the previous season. Time treatment by monitoring for egg hatch in May; turn 10 females upside down and note if crawlers are present among the eggs. Look for mature females under cordons.
When using summer oil sprays, make two applications; apply the first treatment when 50% of the females show egg hatch (i.e., there are some crawlers below them), repeat monitoring again in 2 weeks and apply the second treatment when 90% of the females show crawlers. Alternatively, treat with imidacloprid when 90% of the females show crawlers. High temperatures in the summer months may reduce scale numbers. If numbers are high in September and grapes have been harvested, apply a treatment of oil before mid-October. In late season varieties or cool regions where harvest is late, an oil treatment may not be effective if the second instars have already moved under the bark for the winter.
When monitoring late in the dormant season, watch for ants. If ants are present, look closely for mealybugs and lecanium scale as outlined in DELAYED-DORMANT AND BUDBREAK MONITORING (wine/raisin grapes or table grapes) and record your results on a monitoring form (example form— ).
UC IPM Pest Management Guidelines: Grape
Insects and Mites
L. G. Varela, UC IPM Program and UC Cooperative Extension, Sonoma County
Acknowledgment for contributions to Insects and Mites:M. C. Battany, UC Cooperative Extension, San Luis Obispo County
J. Granett, Entomology, UC Davis
P. A. Phillips, UC IPM Program, Ventura County
A. H. Purcell, Environmental Science, Policy and Management, UC Berkeley
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