Plague thrips
Plague thrips (Thrips imaginis) are a native insect that are primarily a concern when present in large numbers from pink bud to early fruit set. They can damage both pome and stone fruit.
Pest identification
Adult plague thrips are visible to the naked eye and can be seen during flowering, crawling on petals and around the reproductive parts of the flowers. They are usually brown, narrow-bodied and about 1.0–1.3 mm long.
Damage
Plague thrips can damage temperate fruit crops in 2 main ways. Firstly, when they are present in very large numbers, their feeding on flowers results in damage to the stamens and stigmas, thereby affecting pollination and fruit set. Secondly, feeding on the developing fruitlet surface causes a russet to develop that becomes unsightly as the fruit grows, making it unmarketable.
Monitoring
Monitor for plague thrips using yellow sticky traps placed throughout the orchard from bud burst to shuck fall. The traps can indicate thrips activity levels and can also be used to obtain a formal identification of the pest species.
Monitor plague thrips activity by tapping flower clusters over a white ice cream container (or similar). Inspecting individual flowers can also help determine a measurable population size (i.e. thrips/flower) and damage, which will appear as brown spots on the stamens and stigmas.
Plague thrips are known to migrate in large numbers on the wind and can invade an orchard very quickly. Regular monitoring will help to identify any sudden increases in thrips numbers.
Management
Cultural and physical: avoid mowing orchard inter-rows and adjacent pastures at or just before bloom as this might drive thrips into the crop.
Biological: there are several natural plague thrips predators including predatory mites, bugs, lacewings, predatory thrips, lady beetles and parasitic wasps. However, these are unlikely to provide complete control of plague thrips, particularly during periods of rapid pest influx.
Chemical: an effective control program for plague thrips will be based on strategic spraying that is informed by monitoring and observation. When spraying at or around bloom, be particularly aware of any label warnings and recommendations for protecting bees and other off-target species. Refer to the Orchard plant protection guide for chemical suggestions.
