Crop Protection

Novel refuge boosts earwig numbers in orchards to aid pest control

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16 April 2022, UK: Encouraging beneficials into orchards using artificial refuges is assisting the control of damaging pests while helping to reduce applications.

Orchard managers currently have access to a range of pesticides that offer good control of damaging insect species. But for how much longer?

Agrochemical products are under mounting pressure from revocations and restrictions, pest and disease resistance and reduction of residue levels.

Alex Radu, Agrovista’s fruit technical manager, says: “The fruit sector is examining alternatives to conventional plant protection products, especially insecticides. The role of integrated pest management is growing and its principles now form the backbone of our agronomy advice.

“We are likely to lose approval of some important insecticides over the next few years, and with others we might have to cut the number of applications and/or reduce rates. We need to assess other forms of pest control, such as using biopesticides and putting beneficial predators to good use.”

Agrovista has worked with NIAB EMR, Russell IPM, University of Greenwich, Worldwide Fruit and Fruition on an Innovate UK project to develop a method to help encourage beneficial predators into orchards. “As a company we work hard behind the scenes looking for improvements, and this is a great example of IPM development in action,” says Alex.

“The project came about following discussions among growers, agronomists and entomologists who thought it would be very helpful to develop shelters for beneficials, especially earwigs, in orchards.”

Voracious predators

Earwigs are voracious predators and when present in good numbers reduce the levels of some very important orchard pests, such as woolly aphids, rosy apple aphid, codling moth and pear sucker.

They are a valuable ally in orchard management, but their numbers, as well as those of other beneficial predators, can be affected by lack of shelter, food, as well as some PPP applications.

The aim of the Innovate UK project was to try to find a solution for these problems. Trials on different sites came up with the finalised product, the Wignest refuge, which is now available to UK growers.

The Wignest offers shelter to earwigs, ladybirds, spiders, Anthocorid bugs and lacewings and also contains a supply of earwig food attractant.

The refuge is attached directly to trees or on post-and-wire systems, and lasts for a number of seasons.

Boosting earwig numbers

“Introducing Wignests is an easy solution to help protect earwigs and boost their numbers,” says Tom Johnson, Agrovista fruit agronomist and precision lead. “It makes perfect sense for today’s orchards. “The most obvious benefit is the protection they provide, not just in terms of a home but also from certain applications throughout the season. In older orchards there are plenty of cracks in the bark for shelter, but in intensive, young orchards there are not enough to provide effective refuges.”

This was the main reason for developing the Wignest. However, it also offers a source of food to help overcome shortages, particularly early in the season when orchard pest control removes the majority of the diet of these beneficial predators.

“This can be particularly damaging as young earwigs rely on a plentiful food supply in early spring,” says Mr Radu. “Adult females overwinter in the soil and after egg hatch takes place, they care for their offspring in the nest.

“The mothers start foraging for insects to feed their young, but if early chemical pest control has taken place, food may be very scarce. This may prevent a big enough earwig population being established, compromising their positive effect on pest numbers through the remainder of the season.”

The food source within the Wignest is sufficient for about three years. The shelter itself is a robust wooden structure with a protective a plastic top so will last a lot longer, by which time predator levels should be sufficient to reduce reliance on insecticides.

Effective control

The recommendation is to place one of these refuges per tree to get the most benefit, but expert entomologists think that attaching them to every third tree can still provide effective control.

“The system is quite simple,” says Mr Radu. “You attach each Wignest to a branch or the support system. Beneficials will find them and naturally take refuge during the day.”

Wignests can also be used to speed up the establishment of beneficials in young orchards by first placing them in older orchards, where predators are already plentiful, in the preceding season.

They can then be removed in October/early November and introduced to the young orchard, where the females present in the refuges will nest, providing an instant boost in earwig numbers in the spring.

“Trials show two to three earwigs per tree are enough to keep woolly aphids under control,” says Mr Radu. “Where artificial refugees were introduced, earwig numbers increased and woolly aphid colonies were reduced. “If predator levels are high enough, some insecticide applications may not be necessary. Where numbers are lower, necessary insecticide applications, which would be applied during the day when earwigs are in the Wignests, leave these and other sheltered beneficials unharmed and ready to mop up remaining pests.”

Crops should be monitored to assess the need for additional control. “You need to evaluate the correlation between beneficials and pest numbers and apply control when thresholds are reached. “Without beneficials, you will be 100% reliant on insecticides, and two applications to control pests in a young orchard would be common practice, and more might be needed.”

Each Wignest costs less than £1. Even when spread over three trees, that and the cost of placing them represents a significant outlay. “Adopting this system will very much depend on the ethos of the grower as for the time being we still have insecticides that enable us to obtain good pest control.

“With Wignest you don’t see an instant result like with a conventional insecticide, but we are losing chemistry and PPP active loading per hectare is reducing in some cases, so the pressure to find alternatives is increasing.” Mr Radu suggests growers could try a small area in the first instance.

For example, the system could be installed in a young orchard where predators have difficulty establishing, and numbers and effectiveness of pest control could be monitored over the following couple of seasons. “This will provide a good indication of how the refuges are working for you, and you can then decide about expanding the area with Wignests to elevate predator numbers more quickly to provide long-lasting protection.”

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