If you’ve been reading the last few blog posts, you will see that Cornell, Iowa State, and the University of Kentucky have been collaborating on a project to optimize the efficiency of using a new barrier strategy called “mesotunnels” to help organic growers protect cucurbit crops from pests and diseases. Cucurbit crops can suffer from the severe feeding damage from cucumber beetles, squash bugs, and squash vine borer, as well as the diseases that those insects transmit: bacterial wilt and cucurbit yellow vine disease (CYVD). Mesotunnels are covered with a nylon mesh fabric and supported with 3 ½ ft. tall bent EMT conduit hoops. The nylon mesh fabric is breathable and light-permeable, but its small mesh size keeps out insect pests throughout the summer growing season.

Despite offering protection from insect pests, there are still challenges to using the mesotunnel system. These challenges include how to manage pollination (cucurbits are very dependent on pollinators), how to manage weeds, and how to manage other diseases that are not insect-vectored, such as powdery mildew and downy mildew.

In 2020, UK had three different experiments that addressed these challenges. For the pollination experiment, we used acorn squash ‘Table Ace’ and muskmelon ‘Athena.’ For the weed and disease experiments, we used acorn squash ‘Table Ace’ only. Experiments were conducted at the UK Horticulture Research Farm in Lexington, KY on USDA certified organic land.

1. Pollination Experiment

We had two different crop experiments for the pollination trials. The acorn squash pollination experiment was conducted on 120-ft-long plots, three beds wide on 7’ centers (21’ by 120’). The muskmelon pollination experiment was conducted on 30-ft-long plots, three beds wide on 7’ centers (21’ by 30’). For both crops, we had four treatments that were replicated four times and in a randomized experimental design. Our treatments included:

• On-off (a traditional grower method where the netting was put on at transplant and removed at flowering for the remainder of the season)
• On-off-on (the netting was put on at transplant, removed at flowering for pollination purposes and then replaced after pollination was complete)
• Full season (the netting was put on at transplant and remained on the crop for the entirety of the season, but purchased bumblebees were placed under the netting to provide pollination)
• Open ends (the netting was put on at transplant and remained on the crop for the entirety of the season; however, at flowering, the ends were opened to allow pollinator access and then closed after pollination was complete.)

2020 Pollination Experiment Results

We found in the acorn squash pollination experiment strong evidence that just opening the ends to allow for pollination gave the best yields. There was a significant increase in marketable acorn squash yield in the open-ends treatment compared to all other treatments.

We also found that the number of bees under the 120 ft long plots of acorn squash was greater in the open-ends and on-off treatments compared to the full season treatment.

In the muskmelon pollination plots, we found that the full season (stocked bumblebees) and open ends treatment had comparable marketable yield compared to the on-off and on-off-on treatments.

 2021 Plans for Pollination Experiments

Based on the results from our 2020 experiments, we are replicating the acorn squash experiment in 2021. We will have the same four treatments of on-off, on-off-on, full season and open ends to determine if the open-ends treatment consistently produces a higher marketable yield.

2. Weed Management Experiment

Acorn squash was used for the weed management experiment. Plots were 30 ft long, 3 beds wide on 7’ centers (21’ by 30’). We had four treatments, replicated four times and in a randomized experimental design. Our treatments included:

• Low seeding rate of teff (an Ethiopian grain): 12 lbs/A (coated seed)
• Medium seeding rate of teff: 24 lbs/A (coated seed)
• High seeding rate of teff: 36 lbs/A (coated seed)
• Buckwheat: 90 lbs/A seeding rate

2020 Weed Management Experiment Results

We found that the high teff treatment had significantly lower weed biomass compared to the low teff treatment. However the difference wasn’t statistically significant from the buckwheat vs. medium teff treatments.

We also found no significant difference in marketable yield among the four treatments, although the buckwheat treatment did tend to have lower yield.

2021 Plans for Weed Management Experiments

Based on the results of our 2020 weed management trials, we are modifying 2021 treatments. Because Iowa State found higher yield with a landscape fabric treatment, we are including landscape fabric this year. We are also experimenting with mowing the cover crop to determine if that helps prevent the cover crop from interfering with the acorn squash and potentially competing for nutrients and water. Therefore, our treatments for 2021 are:

• High teff- mowed (36 lbs./A coated seed)
• High teff- unmowed (36 lbs./A coated seed)
• Buckwheat- mowed (90 lbs./A)
• Landscape fabric

3. Disease Management Experiment

Acorn squash plots were 30 ft long, 3 beds wide on 7’ centers (21’ by 30’). We had four treatments, replicated four times and in a randomized experimental design. Our treatments included:

• Control: no row cover, no spray (insecticide or fungicide)
• Spray only (insecticides: Bt, kaolin clay, Azadirachtin/pyrethrins; fungicide: cuprous oxide): no row cover
• Row cover and spray: received both the netting and a spray (insecticides and/or fungicides)
• Row cover only: no spray (insecticides or fungicides)

We surveyed for insect pests such as cucumber beetles and squash bugs and for non-insect vectored diseases such as powdery mildew and downy mildew.

2020 Disease Management Experiment Results

We found that the row-cover-only treatment reduced the incidence of powdery mildew by about 20% compared to the control that was not covered or sprayed. The spray only treatment also has a great effect at reducing powdery mildew incidence; however, when you take the row cover and the spray treatment together as an additive effect, the effect is not as great. We speculate that perhaps the row cover could be preventing the spray from effectively getting to the plants. We also found that the row cover treatments had a higher yield regardless of whether it was sprayed or not.

 

2021 Plans for Disease Management Experiment

For 2021, we are replicating the same experiment as in 2020. We will still have the four treatments: control, row cover only, spray only and row cover and spray. We will also do a side experiment to calibrate our boom sprayer to see the actual difference between spraying the netting and spraying without netting. There may be a speed or rate that provides better penetration through the netting, or we may find that the spray penetration is comparable between covered and uncovered at the same speed/rate.

We will continue to update you all as the season progresses. Be on the lookout for videos of how we scout under the netting, how we mow the living mulch cover crop and how we make our new “gravel snake” weights!

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