You Shall Not Pass: Using Mesh to Limit SWD Damage

Written by Nick Buck:  Spotted Wing Drosophila (SWD) is a fruit fly native to S.E. Asia, capable of causing yield reductions by ovipositing in soft and stone fruit. Insect exclusion mesh is one method of control which acts as a protective barrier, inhibiting entry of SWD into the crop, reducing egg laying in the fruit once it ripens.

Several studies have focused on the use of mesh to limit soft fruit damage by SWD.

• In raspberry high tunnel systems mesh reduced the presence of SWD adults (48%), eggs (70%) and larvae (58%) in the crop, compared to unmeshed tunnels.
• On blackberries, mesh placed over the crop reduced SWD egg laying by 92% when compared with open control plots treated with an organic insecticide.

Studies on the effects mesh has on other pests and natural enemies have also been carried out.

• Mesh reduced overall pest numbers by 35.5% (mites-24%, thrips-20%, aphids-46%), but also reduced numbers of natural enemies including parasitoid wasps (26%) and spiders (32%).

It is possible that mesh also impeded other ecosystem services such a pollination. Data was collected in 2021 to measure the impact of mesh on pollinators numbers visiting raspberry flowers and resulting fruit quality.

My pilot data in 2019 showed raspberries produced under meshed tunnels had 12% higher incidences of sooty shoulder, a black residue developed on raspberries due to high humidity. Hence, as part of my PhD I also investigated whether microclimatic changes caused by mesh, coupled with an inability to fully vent tunnels reduced air flow and altered temperature and humidity. This data will be analyzed in the coming months.

Poor mesh management and late implementation on some sites in the 2021 study led to slightly higher numbers of SWD emerging from fruit in meshed tunnels than unmeshed tunnels. As a result, it is recommended that for maximum SWD control mesh should be deployed at the first sign of ripe fruiting and kept in place until the end of harvest.

Polytunnel with mesh netting on the side next to an open control tunnel.

Inside one of the meshed raspberry polytunnels.