Netting Proves Effective in Putting Cherry Pests in Their Place

Spotted wing drosophila (SWD) and bird damage pose significant challenges to Michigan sweet cherry growers. The risk of SWD and bird damage vary with weather conditions. Netting might prevent damage from both these pests in all weather conditions and is feasible in short, high-density plantings of sweet cherries. We tested the effectiveness of netting designed to keep out insects like SWD and, consequently, birds of any size. We also assessed netting effects on fruit quality metrics and environmental conditions.

Installing Nets 

In 2023 and 2024, we conducted an experiment at the Clarksville Research Center and the Northwest Michigan Horticultural Research Center. We encased sections of high-density sweet cherry rows in netting after pollination but two to three weeks before harvest. Each net was paired with an adjacent, unnetted row of the same variety, to serve as the control.

With the help of a platform, we draped netting over the top supporting wire between posts. Since SWD are so small, the net must have no gaps to ensure insects cannot get inside the net. To seal our nets, we wrapped the bottom of the net on the ground around PVC tubing and staked it in place. The edges of the nets at the ends of rows were then rolled together and clipped with large binder clips.

Nets were kept close to the trees to allow tractor access. Insecticides and fungicides were applied on both the netted and control areas at the same time during both growing seasons.

Pest Damage and Abundance 

Bird damage: At harvest, nets were removed and cherries with bird damage were counted. When compared to unnetted controls, nets significantly reduced bird damage in 2023 and 2024.

SWD flies and larvae: Every net and control site had an SWD lure and trap that we checked once a week to track adult SWD abundance as the cherries ripened. For larval counts, cherries were collected at harvest and larvae were extracted from cherries using a brown sugar method. There were few SWD in 2023, likely due to the dryness of that growing season. In 2024, however, SWD pressure was much higher, and the netted sites had significantly reduced adult and larval SWD compared to unnetted control sites.

Environment and Fruit Quality 

We wanted to test whether the fine mesh of netting affected temperature and humidity. Does the net decrease the temperature for the cherries? Is humidity increased under the net? To try to address these questions, we tracked humidity and temperature with small environment monitoring devices. We found no significant differences in temperature or humidity between netted and control sites.

In addition to tracking environmental data, the following fruit quality measures were taken:

Results showed several positive effects of netting with only one potential negative effect where the percent soluble solids metric was lower under the nets when compared to the unnetted control in one year.

For more considerations about protective netting on cherries, continue reading at canr.msu.edu.