Investigating biological controls for western flower thrips

A Welsh soft fruit grower who once lost his strawberry harvest to an insect pest is working with ADAS to establish colonies of a predatory bug in the crop before and during the flowering stage to find an effective biological control alternative to insecticides.

Western flower thrips (WFT) and several other thrips species, are the nemesis of strawberry growers. No more so than at Bellis Brothers near Wrexham, where thrips wiped out a crop worth £25,000 three years ago.

Even when using chemical controls, the business will lose an average of 5-10% of its outdoor-grown strawberry fruit to thrips in any given year.

Alternative and more environmentally friendly thrips controls are urgently needed particularly as WFT is widely resistant to insecticides. There are also concerns that other thrips species that damage strawberries could also build up resistance in the future.

With thanks to funding from the Farming Connect ‘Try Out Fund’, Adrian is working with ADAS horticultural entomologists to investigate if a predatory bug, Orius laevigatus, could be a reliable weapon against future thrip invasions.

Challenges hen introducing predatory species

Establishing Orius early

An obstacle to introducing Orius predators into the 60-day strawberry crops at Bellis Brothers is the plant’s short flowering period. This can prevent Orius colonies establishing and building up enough numbers before adult thrips fly in and attack during flowering.

To help overcome this, Alyssum, a potential trap plant for thrips and a ‘banker plant’ for Orius, was planted as a companion crop in the strawberry crop. ADAS released Orius several weeks before the strawberries flowered to provide it with an early source of pollen. This would allow it to establish in sufficient numbers to control thrips as they fly in.

“Orius was provided free of charge by Biobest UK Limited’’ ADAS Senior Research Entomologist Jude Bennison explained.

As the strawberries come into flower the hope is that the predators will move onto these and prevent fruit damage.

“Another biological control agent, a predatory mite, can be effective on strawberries but they only consume thrips larvae,’’ said Jude.

“The mite is effective against WFT which produces large numbers of larvae in strawberry flowers. Other species of thrips that fly in as adults do not seem to produce many larvae on strawberry. Orius is a better option as it will prey on the adults as well as larvae.’’

“If the principle behind the trial can be proven, it could be linked to a bigger project and rolled out on a bigger scale”, added Dr Andrew Gladman, ADAS Research Entomologist.

Proving effectiveness with outdoor grown strawberries

Bellis Brothers uses tabletops to grow four acres of strawberries. A sequential planting system extends the fruiting period for up to eight weeks.

Because the fruit is grown outdoors for pick-your-own, it is more of a challenge to use Orius than in polytunnel or glasshouse crops as it needs warm temperatures to lay eggs and develop.

The cool, wet weather during May and early June this year wasn’t ideal for Orius.

Mr Marks, who runs the business with his wife, Lizzie, and her parents, Roger and Joan Bellis, says his goal is to manage pests and diseases without relying on chemicals and the negative implications of these for the environment and beneficial organisms.

“We hope that these entomologists can work their magic so that we have proven biological controls that can be effective on outdoor-grown strawberries, he said. “It is why we applied to take part in this trial.’’

Other Integrated Pest Management methods

ADAS Senior Horticutural Consultant Chris Creed also recommends encouraging wild predators. These can be more tolerant to pesticides within integrated pest management (IPM) programmes than commercially available predators.

This could mean introducing or allowing the growth of other companion plants such as nettles which provide habitat and food for predators.

Growers should carry out regular crop inspections throughout the growing season, he advised.

“Either monitor the crops yourself or use an agronomist. There should be a lot of crop walking and checking and making key decisions,’’ said Mr Creed.

Many horticulture businesses are moving towards IPM, only using chemical controls when absolutely necessary.

Farming Connect horticulture sector officer Hannah Norman said the results of the trial at Bellis Brothers will be shared with other growers once the project concludes.

The Try Out Fund allows growers and farmers opportunities to be innovative and to trial different ways of doing things, she added.

To read about our research and consultancy services in relation to this work, please visit our Integrated Pest Management for Horticulture service webpage.

For further information on this project or our services, please contact ADAS Senior Research Entomologist Jude Bennison.