Plague thrips are a native insect that is primarily a concern when present in large numbers from pink bud to early fruit set. They can damage both pome and stone fruits.
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 (Figure 1).
They are usually brown, narrow-bodied and about 1.0–1.3 mm long.
Damage
Plague thrips can damage temperate fruit crops in two 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 (Figure 2).
Monitoring
Monitor for plague thrips using yellow sticky traps (Figure 3) placed throughout the orchard from budburst to shuckfall.
The traps will give you an indication of thrips activity 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. numbers/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 in a very short time. Regular checking 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 enemies of plague thrips including predatory mites, bugs, lacewings, predatory thrips, lady beetles and parasitic wasps.
However, these are unlikely to provide full 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 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.
Download the Orchard plant protection guide
See this article in Tree Fruit Sept 2021
