Screening can be an effective measure to exclude unwanted pests from colonizing your crops. In high tunnels, one of the biggest challenges to successfully implementing exclusion screening is managing the unintended side effect: reduced airflow. In spring we are clamoring to get inside the warmth that high tunnels provide, but by mid-summer they can become one of the most dreaded environments to work in. The temperatures inside high tunnels beyond mid-June can quickly exceed those suitable to plant growth. The key to maintaining crop production during this time is proper ventilation. Therefore, selecting an insect screen that will effectively exclude pests while minimizing reductions in airflow is crucial. We have been investigating the ability of such screens to keep biological control agents in and cucumber beetles out while maintaining a suitable growing environment for cucumbers, tomatoes and melons.
We have looked at three different insect screen sizes over the past few years: small (0.40 x 0.45 mm), medium (0.26 x 0.82 mm), and large (1.00 x 4.00 mm) pore sizes. It was immediately obvious that one of them was not suitable. The small screen size increased temperatures inside the high tunnels 6˚F on average, even more on the hottest days, and led to temperatures exceeding plant growth and development limits the majority of the season (Figure 1). It also made it unbearable to work in these tunnels. We saw no changes in temperature or relative humidity in tunnels covered with the medium or large screen sizes (Figure 2).
Figure 1. Temperature profiles across 2 years (2014-2015) as a result of the small insect screening installed to cover all ventilation openings compared to open tunnels.
Figure 2. Temperature profiles from 2016 comparing open tunnels, medium screens and large screens covering all ventilation openings.
When growing melons in the screened tunnels, we used commercially available bumble hives to achieve pollination. Harvest was highest in tunnels with the medium sized insect screen (Figure 3), which may be attributed to the exclusion of cucumber beetles and bacterial wilt. Therefore, we would recommend the medium sized screen (0.26 x 0.82 mm) to exclude cucumber beetles or similar-sized insect pests. We did not identify a screen size that would eliminate aphids and the diseases they transmit.
Figure 3. Yield comparison among open tunnels, medium and large screens in 2016.
When considering installing insect exclusion screening on your high tunnels, first identify the pests that you are hoping to exclude. Consider the cost of the materials in addition to the potential for incorporating pollinators depending on the crop, savings in alternative pest management and the longevity of the material. We used the screens for two years during our testing and left it on the tunnels throughout the winter. There was minimal deterioration observed and we predict that they could be used for at least 3 years, if not more.
Ian Kaplan contributed to this article.