Before we launch into the second field season in our 3-year project¹, let’s look back to the 2020 season and reflect on what we learned. This blog post focuses on the 2020 trials in Iowa; later posts will summarize the 2020 field trials in Kentucky and New York.

The aim of our field trials is to find out how a new barrier strategy called “mesotunnels” can help growers of organic cucurbit crops. Mesotunnels can keep damaging pest insects – cucumber beetles, squash bugs, and squash vine borer – away from plants by shielding the plant rows with a nylon mesh fabric (ProtekNet® or ExcludeNet®) supported on hoops. This barrier can also stop damaging bacterial diseases, including bacterial wilt and CYVD, that are spread by cucumber beetles and squash bugs, respectively. Because the nylon mesh is breathable and the hoops are fairly tall (3.5 ft), mesotunnels have potential to provide protection through most or all of the growing season.

In Iowa in 2020, our trials were on muskmelon (cv. Athena) and acorn squash (cv. Table Ace). For each crop, we conducted two trials: one focused on ensuring pollination, and the other on managing weeds in the alleys between black-plastic-mulched crop rows. The trials were done on certified organic ground at the Iowa State University Horticulture Research Station (ISUHRS) near Gilbert, IA. All farming practices followed OMRI-approved methods.

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Pollination trials. These took place on triple-row, 150-foot-long mesotunnels with 6-ft spacing between rows (figure 1A). We used this fairly large scale to approximate commercial-scale farming situations. For each crop, we had three treatments, each of which was replicated four times in a randomized complete block experimental design. The treatments were:

• Mesotunnels closed all season, with a purchased hive of bumble bees (from Koppert, Inc.) placed underneath to provide pollination ("full season")
• Mesotunnels opened completely for 2 weeks during flowering of the crop, then re-closed ("on-off-on")
• Mesotunnel ends opened for 2 weeks during flowering ("open ends")

The on-off-on and open-ends treatments depended on natural pollinators (honey bees and many species of native bees) rather than purchased bees. Based on the results of scouting, organic insecticides were sprayed on uncovered plots when thresholds were reached.

Here’s what we found in the pollination trials:

• For muskmelon, marketable yield was highest for the full-season treatment, intermediate for the open-ends treatment, and lowest for the on-off-on treatment.
• For acorn squash, in contrast, marketable yield was highest yield in the on-off-on treatment, lowest in the full-season treatment, and intermediate in the open-ends treatment.

Why were the outcomes different for the two cucurbit crops? Here are some possible reasons:

1. Acorn squash fills the space inside the mesotunnels by the time female flowers start to appear. In contrast, muskmelon has a smaller, lower canopy. The result for the full-season treatment is that bees could find flowers much more easily in the muskmelon tunnels than in acorn squash – which translated to higher yield in the muskmelon than the squash
2. Compared to squash, muskmelon is more vulnerable to bacterial wilt in the Upper Midwest. Sure enough, we saw considerably more bacterial wilt symptoms on the treatments that uncovered muskmelon (entirely or just on the ends) during the 2-week pollination period than on squash. So the full-season treatment came out on top for muskmelon partly because it benefitted more from complete cucumber beetle and disease protection.

Weed management trials. These trials were done on both crops in triple row, 30-ft-long subplots, in full-season mesotunnels with purchased bees used for pollination (figure 1). The four treatments (replicated four times in a randomized complete block experimental design) were:

• Polyethylene landscape fabric
• Teff (a cereal crop used as a mulch) seeded at 4 lb/acre
• Teff at 8 lb/acre
• Bare ground (control).

 

Here’s what we found in the weed management trials:

• In muskmelon plots, marketable yield for the landscape fabric treatment was about twice as high as for the other three treatments. Teff suppressed weeds almost as well as landscape fabric - but teff also suppressed crop yield at both seeding rates.
• In acorn squash plots, marketable yield was highest for landscape fabric, but the difference with teff was less than for muskmelon. Teff treatments out-yielded the bare-ground control.

How did we interpret these results?

1. The yield penalty from teff in both crops could be caused by root competition with the crop for nutrients, water, and sunlight. By digging around, we noticed very extensive root growth by teff from the soil strips into the plastic-mulched crop strips.

Take-home lessons for 2021 Iowa field trials. Based on our 2020 experiences, we’ll modify the 2021 weed management treatments as follows:

• Landscape fabric
• Teff seeded at 4/lb acre – not mowed
• Teff seeded at 4 lb/acre – mowed at mid-season when covers are removed
• Bare ground control – not mowed
• Bare ground control – mowed wat mid-season when covers are removed.

By mowing teff about 3-4 weeks into the growing season, we hope to get the benefit of teff’s early-season weed control while minimizing yield drag due to its competition with the crop. Another change is that acorn squash weed trials will switch to an on-off-on strategy (2 weeks with covers off during bloom) to allow for better pollination via natural pollinators rather than purchased bees. In contrast, the muskmelon weed management trial will stay with full-season mesotunnels and purchased bees because this strategy had the highest yields in 2020.

We’ll have in-season blog reports from the upcoming season as well as summaries at the end of the season. Stay tuned!

 

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