Several species of mealybugs are pests of vineyards in many parts of the world. In Australia, the longtailed mealybug (Pseudococcus longispinus) is prevalent in many Australian grape-growing regions. They are considered a minor pest of vineyards, usually being kept below economic thresholds by various beneficial insect species.

Photo: Shane Coster, Research and Development Solutions

They prefer mild warm conditions with temperatures around 25°C and high humidity. While hot dry conditions can reduce mealybug infestation pressure into the latter part of the season, populations can rebuild rapidly if conditions become favourable as conditions cool into autumn. Female mealybugs can lay large numbers of eggs, which quickly hatch into crawlers, and up to four generations may occur each year. Mealybugs overwinter as nymphs in the bark of the vine or even in trellis posts, before emerging in spring to feed.

Mealybugs are soft-bodied sap-sucking insects. Feeding by mealybugs does not usually result in economic damage. However, as they feed, they produce a sugary excretion or honeydew, which encourages the growth of sooty moulds. Sooty mould on vine leaves can reduce photosynthesis and mould on grapes can make the fruit unsaleable or lead to rotting. Heavy infestations of mealybugs can result in premature leaf fall, which may affect the ability of a canopy to mature a crop or store carbohydrates prior to dormancy. Mealybugs have also been identified as vectors for the transmission of grapevine leafroll-associated viruses.

Photo: Shane Coster, Research and Development Solutions
Berries removed to reveal mealybugs feeding in the centre of the bunch, making them difficult to identify.

Detailed field monitoring is integral to the effective management of mealybugs in grapevines. Other strategies for managing mealybug populations include controlling ants around grapevines, (as some ant species will actively protect mealybugs from predators), vineyard floor management (providing cover crops as alternative food sources for parasites and predators), and vine management practices that improve airflow and reduce contact in the vine canopy. Sprays are rarely required, but significant outbreaks in recent seasons have required targeted application of insecticides.