This review covers the problem of western flower thrips feeding, breeding and damaging the flowers and fruits on strawberry crops, particularly ever-bearers.
Which species are involved?
Strawberry growers now successfully implement IPM techniques to control western flower thrips (WFT) but in recent years, fruit bronzing similar to that caused by WFT has occurred where WFT has been satisfactorily controlled. Other thrips species found in the flowers of such crops include the rose thrips (Thrips fuscipennis), rubus thrips (Thrips major), onion thrips (Thrips tabaci) and flower thrips (Frankliniella intonsa).
What do we know about their activity in strawberry?
Where non-WFT thrips species occur, few larvae are found in flowers and it is thought that adults flying in are causing the fruit damage before they start breeding in the crop.
How might we control these alternative thrips species?
- It is believed that sprays of spinosad (Tracer) are currently effective at controlling these alternative species, but like WFT, they could develop resistance, so alternative control measures are required.
- The predatory mite Neoseiulus cucumeris which contributes to the control of WFT, only feeds on young thrips larvae, so may not prevent damage from other thrips species if their adults are causing the damage.
- The predatory bug Orius laevigatus which also contributes to WFT control, predates both thrips adults and larvae, but temperatures are not always high enough for its successful establishment. It is also expensive to release, slow to establish and is susceptible to some plant protection products including spinosad (Tracer).
- Using the long-flowering annual plant alyssm as a ‘banker’ plant in everbearer strawberries can help to establish Orius laevigatus, hasten its dispersal in the crop and speed up control, although some thrips species, including WFT, can also breed in alyssum.
- Some growers of glasshouse crops in mainland Europe use a commercially available pollen (NutrimiteTM) to boost numbers of predatory mites and this might also help Orius establishment but work is needed to test this.
- T. tabaci, T. major and T. fuscipennis larvae are all reported to drop to the ground to pupate, so if larvae do develop on the plants, the ground-dwelling predatory mite Stratiolaelaps may contribute to the control of their pupae
- Entomopathogenic fungi (EPF), such as Beauveria bassiana (Naturalis-L and Botanigard WP) and Lecanicillium muscarium (Mycotal), are recommended for controlling whitefly, but also offer some control of thrips. Their efficacy is thought to be better against adult thrips than larvae and they work best in high relative humidities (60–80% depending on product).
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