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What are growers saying about mesotunnel systems for organic cucurbits?

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Content Author:
Kaitlin Diggins Lois Morton

Row covers are widely used in organic farming to exclude insect pests and disease pathogens. Mesotunnels are a recent variation on this plant protection technology. Mesotunnels are intermediate between low and high tunnels. Their steel conduit hoops are covered with a fine nylon-mesh fabric that permits rain, air, and sunshine to reach the plants inside the tunnel. The mesh fabric and tall hoops (about 3.5 ft) give mesotunnels the potential to protect the marketable yield of cucurbit crops for the entire growing season.

mesotunnel
 A mesotunnel in a cooperator's on-farm plot in Iowa at the beginning of the 2020 growing season.

Along with Cornell University and University of Kentucky, Iowa State University (ISU) has been researching mesotunnels as part of a USDA-funded 3-year organic cucurbit project.1 In conjunction with this project, a number of commercial growers in all three states are trialing mesotunnels on their farms.

Recently, we surveyed some of these cooperators via virtual interviews to learn their experiences and perceptions of mesotunnels for cucurbit crops. They used mesotunnels at a range of heights from 30 to 48 inches in single-row and triple-row plots. After the 2020 growing season, the growers concluded the sweet spot for cucurbit mesotunnels was about 42 inches tall. Depth of the hoops in the ground varied with plot location, weather and wind, soil type, and soil saturation. One grower mentioned their struggle with dry, compacted soil:

 “It [the weather] had been dry prior to install. Even with the pinched ends of those tunnels, they were very difficult to install in the field. We had three or four people on each side trying to push those hoops in, and a lot of them were quite unstable after planting. [Then] we got an accumulation of about four inches of rain over the course of three days so that the soil was very moist, and I was able to go along and push those hoops in and secure them.”

 The growers noted that, by mid-season, the foliage appeared to fill the tunnel at this height, but the hoop ends were pushed far enough into the soil to avoid instability.

mesotunel 2
Foliage is protected by the mesotunnel, which is supported by conduit hoops, in this New York trial.

 

Some growers planted several cucurbit crops under a single mesotunnel that was several hundred feet long. The nylon netting was removed to ensure native pollination when female flowers first became visible. One grower had three varieties under one tunnel, each with a slightly different flowering time. This resulted in an extended pollination period without the nylon-mesh cover protection, and exposed the plants for a longer period to potential insect infestation, pathogens, and weather events. They remarked, “I didn’t observe any diseases, at least during the part of the season when the mesotunnel was installed; I did start to see typical diseases of bacterial wilt and cucumber mosaic virus and things like that, but that was after the mesotunnels [fabric covers] were removed.”

A different experiment used purchased hives of bumblebees placed inside the mesotunnel to avoid removing the covers for several weeks during pollination.

beehive
Purchased beehive in the mesotunnel at ISU, featuring graduate student Sharon Badilla Arias.

There were mixed feelings about introducing bees into the mesotunnels. One grower who used purchased hives stated, “It was really nice to not have to worry about insect pressure, but as a grower, and as a human being, I really did not like having the bees trapped in the mesotunnel.” Another grower who used hives commented that the bee activity was too low and they were relatively unfamiliar with introduced bees. However, at the conclusion of the 2020 field trial, the grower found that the yields were “up where they should be,” regardless of the initial perception.

Growers' impressions of mesotunnel technology are guiding our research and outreach efforts, providing us with data and feedback of their experiences working with this method of row covers. Later blogs will feature additional insights as we continue field trials this year and next year.

 

1Resilient Systems for Sustainable Management of Cucurbit Crops. Award number 2019-51300-30248. USDA Organic Agriculture Research & Extension Initiative (OREI).