Description of the Pest
Presently, the olive psyllid is widely distributed in San Diego County from the coast to as far inland as Valley Center and Fallbrook. It is mainly limited to the coastal areas of Orange County. Populations in Riverside County have only been found from Temecula to Wildomar. One infested site in Carmel Valley (Monterey County) has been recorded. Olive psyllid feeds on olive, Russian olive (Elaeagnus angustifolia) and mock privet (Phillyrea latifolia).
Light tan adults are 2.5 mm long and strong jumpers. Forewings are marked with a few small dark spots. Nymphs are flat, green to tan, and secrete a white waxy coating that covers the entire colony. There are five nymphal stages (0.4 mm to 1.5 mm long). The eggs are elliptical, 0.3 mm long, pale yellow, and attach to the substrate by a pedicel.
Depending on temperatures, with 68° to 77°F being optimal, a psyllid can grow from egg to adult in 3 months. There are three generations per year. In warm temperatures (above 81°F), psyllids are less active. Mortality increases at temperatures above 90°F.
Females lay eggs on the new shoots and buds, with a single female able to lay 1000 eggs or more. The second generation develops on buds and flowers in May and June. The third generation is often unnoticed, appearing in September and October. Adults overwinter in sheltered areas of the olive trunk. In southern California, psyllid numbers decline after June, most likely because it is hot. Numbers remain low until the following spring when buds appear on the trees.
Trees that are heavily infested can have yield losses of 30 to 60%. The olive psyllid damages trees through direct feeding on buds, flowers, tender shoots, and small fruit and also through the production of honeydew, which increases sooty mold development. During olive flowering and fruiting, psyllid waxy secretion cause flower and small fruit drop and yield reductions. Large populations may retard the growth of young trees.
Even though the second generation causes the most damage, reducing the population size of first generation will help to keep the second generation small. Control measures should be taken before psyllids start secreting their heavy waxy coating, which protects them from pesticides.
Due to its recent introduction, natural enemies feeding on olive psyllid have not been studied, but efforts are underway to identify potential natural enemies in California. Researchers are seeking exotic natural enemies from locations in Europe where the psyllid may be found.
In areas with hot temperatures, psyllid numbers may be reduced by pruning out center limbs to enhance air circulation.
Monitoring and Treatment Decisions
While it is still not known what impact psyllids have on olive trees, it appears that they can tolerate low numbers of psyllids without economic damage. Monitoring between March and May is most useful. General monitoring guidelines for psyllids are:
- Less than 6 per flower cluster: no loss occurs
- More than 6 to 8 per flower cluster in years with low set: some loss may occur
- Less than 10 per flower cluster in heavy set years: no to little loss occurs
- More than 10 per flower cluster: loss may occur