Empowering growers to manage thrips in strawberries

EMPOWERING GROWERS TO

MANAGE THRIPS IN STRAWBERRIES

Words by Emma Smith : Plant & Food Research Ltd

A tiny insect that feeds on strawberry leaves, pollen and fruit is causing a huge amount of damage.

Thrips, a pest causing reduced fruit production, removal of plants and rejection of fruit, costs New Zealand strawberry growers $37,500 per hectare. Current practices to manage thrips in New Zealand are heavily reliant on insecticides. A Sustainable Future Farming project ‘Future-proofing thrips management in strawberries’ is working to address this problem by developing an Integrated Pest Management (IPM) programme for the strawberry industry. This is a collaborative project with Berryworld Ltd, Strawberry Growers New Zealand and the biological and agrichemical industries. “IPM programmes require knowledge of the whole ecosystem,” says Plant & Food Research (PFR) science team leader, Jessica Vereijssen. “You have to understand the pest organism, where they live, and their seasonality. There will not be one single management solution, but a combination of tools that together have an effect on reducing the pest population.” The three-year project will empower strawberry growers to adopt IPM strategies for more sustainable and profitable growing. “We want to take a proactive approach and start working on sustainable solutions for thrips management now, before we need to,” says PFR scientist and project lead, Mette Nielsen.

The aim of the first year of the project was to find what species, of the 6,000 thrip species worldwide, are present in New Zealand strawberry crops, so they can be targeted effectively

“We have learnt from growers in parts of Australia who reached a point where the sprays weren’t working at all, and they were forced to change to an IPM programme almost overnight, scrambling to reform.” The aim of the first year of the project was to find what species, of the 6,000 thrip species worldwide, are present in New Zealand strawberry crops, so they can be targeted effectively.

FOUR SPECIES OF THRIPS WERE FOUND IN AUCKLAND, HAWKE’S BAY AND LINCOLN

1 intonsa flower thrips (Frankliniella intonsa) 2 New Zealand flower thrips (Thrips obscuratus) 3 Western Flower Thrips (F. occidentalis)

4 Onion thrips (Thrips tabaci)

Researchers at PFR collected flowers and leaves from strawberry blocks across Auckland, Hawke’s Bay and Lincoln and found four species of thrips present. The species varied by region, by growing system and over the season. In Auckland, the most dominant species present were intonsa flower thrips (Frankliniella intonsa) along with New Zealand flower thrips (Thrips obscuratus), whereas western flower thrips (F. occidentalis) dominated Hawke’s Bay. In Canterbury, strawberries grown in greenhouses were predominantly infested with onion thrips (Thrips tabaci). Before management solutions to target thrips could be developed, a trial was conducted in the lab to assess the potential damage the different thrips species could cause. “The intonsa flower thrips were found to create the most damage, causing the scarring that downgrades the fruit,” says Mette. “Western flower thrips were also found to cause damage, while the effects of onion thrips were not conclusive.”

The second year of the project comprised a demonstration trial at an Auckland strawberry grower to showcase implementation of a full IPM programme. Beneficial insects were released to manage the thrips and sticky traps were used for mass trapping and to monitor the thrips’ abundance and the species present. “Even though there was still some damage to the fruit, the grower was very happy with the results,” says Mette. “We only put on a single IPM-friendly insecticide spray.” This year, the final year of the project, a similar trial is being run with three Auckland growers, who each use a different growing system, to see if similar results can be achieved. Monitoring of pests and beneficial insects will again be a very important part of the trial, on which to base management decisions. Another trial is being conducted to test how efficient different types of predators are at attacking and killing the thrips pests that we know are causing this economic damage to New Zealand strawberries. The trial will further researchers’ understanding of how well the predators are performing before their release into the strawberry crops. Collaborating with growers is a significant part of the solution to managing thrips. Workshops were planned for growers in Auckland, Waikato and Lincoln to provide knowledge of why and how to build an IPM programme, as well as how to find and identify thrips and beneficial species in their crops. Due to Covid-19 restrictions, workshops have been placed on hold, with videos and online tutorials planned instead. “The strawberry growers have been wonderful to work with and provided great feedback,” Mette says. “They have jumped to be part of the trials and have a great attitude toward doing things better. It has made a huge difference to the success of the project.” Ultimately, the researchers would like to see as many tools available as possible so growers can build their own tailored IPM programmes. Each strawberry block is different and will need a different combination of tools for IPM to be successful.

“We want to enable growers to make their own decisions,” says Mette. “IPM is more dynamic than a spray programme, so you need excellent monitoring systems put in place to have an understanding of what is going on in your crop and the ability to respond to changes as soon as possible.”