Thursday, 22 April 2021
Western flower thrips is a significant pest of strawberry crops. While other thrips species are also suspected of damaging the crop, Scott Raffle explains why an effective IPM strategy for western flower thrips is still your best line of defence.
Western flower thrips (WFT) causes bronzing damage in strawberry crops. We have recently identified other thrips species living in strawberry crops which may also cause similar bronzing. These include rose thrips, rubus thrips, onion thrips and flower thrips.
We suspect these thrips species arrive as adults. This means the predatory mite Neoseiulus cucumeris, which is used to control WFT, won’t work on these other thrips species as it predates on larvae and not adults.
Effective IPM strategies need to be developed for these other species, but in the meantime, here are five recommendations to help you control WFT based on our research:
1. Release the predatory mite Neoseiulus cucumeris
Neoseiulus cucumeris should be released throughout the season from the first flowers.
The minimum release rate should be 25 per plant every week or fortnight, increasing to 50 per plant if the numbers of thrips start to increase.
This predator feeds only on young thrips larvae, so it may not control rose thrips, which might not breed in strawberry flowers.
2. Apply the ground-dwelling predatory mites Statiolaelaps scimitus
Formerly known as Hypoaspis miles, these should be applied once at about 10 per plant.
It is not yet known how effective these are against larvae of thrips species other than WFT that might drop to the ground to pupate, but as they are effective against WFT, it is a sensible option.
3. Release Orius laevigatus in addition to cucumeris once temperatures are suitable
This predator needs a minimum of 15°C for egg laying and over 20°C for good establishment.
Commonly used release rates are a minimum of 0.25 to one Orius per plant, repeated after two weeks.
Orius laevigatus is very sensitive to plant protection products, so avoid using any that are harmful (consult your supplier or adviser).
4. If you see bronzing, consider using an IPM-compatible plant protection product
Options include spinosad (Tracer), but growers may wish to reserve this for control of spotted wing drosophila.
Do not use Tracer if only WFT are present as they are likely to be resistant to this product.
5. Accurately identify your thrips species
Thrips species identification can only be confirmed using a high-power microscope and specialist expertise. Consult your adviser on getting the thrips species identified and choosing the appropriate plant protection product, if required.
Is western flower thrips or another thrips species damaging my strawberry crop?
We set out to research alternative thrips species in strawberry crops as we were finding that, even where IPM programmes have successfully controlled WFT, bronzing damage associated with the pest was still common.
Researchers suspected adults of other species could be flying into strawberry crops and causing damage as the predatory mite Neoseiulus cucumeris, which is relied on to control WFT larvae, does not control adult thrips.
As a result, we wanted to understand which thrips species were present in strawberry crops, whether they were responsible for causing damage and how best to manage and control them.
In addition to WFT, the following thrips species appeared in strawberry crops:
- Rose thrips (Thrips fuscipennis)
- Rubus thrips (Thrips major)
- Onion thrips (Thrips tabaci)
- Flower thrips (Frankliniella intonsa)
Although rose thrips had been suspected of causing the damage, confirmation was difficult as different species predominated at different times of the year.
No larvae of rose thrips were found in strawberry flowers, only adults, so it is possible that this species doesn’t breed in strawberry. This would explain why the predatory mite N. cucumeris is not gaining control.
Orius controls both adults and larvae of thrips but only when temperatures are regularly above 20oC for good establishment, so is unreliable every season. It is also very sensitive to a number of commonly used plant protection products. The predatory banded wing thrips (Aelothrips sp.) was found during this study and is known to feed on other thrips larvae, but it is not known if it feeds on adults.
Scott has worked for AHDB for 11 years, having spent three years at HDC and 30 years in the fruit industry in total. Prior to his time at AHDB, Scott was a fruit advisor/agronomist for 16 years with ADAS, specialising in soft fruit and apple and pear storage.