This was the last year of our three-year OREI-NIFA project: Resilient Systems for Sustainable Management of Cucurbit Crops. In 2022, our team repeated two mesotunnel row cover trials conducted the previous year focusing on pollination and integrated pest management.

Questions we were exploring: How well can pollinators do their job within this system? What effects does the type of pollinator (naturally occurring versus purchased bumblebees) have on yield and marketability of muskmelons? How do different weed suppression methods affect insect populations and disease? How well does full season netting compare to insect pests? Can it keep them out?  Lastly, is fruit yield acceptable and fruit quality up to par with consumer demand?

As we have discussed in previous blogs, cucurbit growers, especially organic growers, can find it difficult to control pest populations. Pest control is important to reduce the risk to insect-transmitted pathogens that cause important cucurbit diseases. The main insect pests being evaluated in our trials were: (i) Cucumber beetles that transmit the bacterium, Erwinia tracheiphila, that causes Bacterial Wilt (BW); and (ii) Squash bugs that transmit the bacterium, Serratia marcescens that causes Cucurbit Yellow Vine Disease (CYVD). We also evaluated the impact of the mesotunnel treatments on powdery and downy mildew, and Alternaria leaf spot (ALS).

How did it stack up in 2022?

2022 Pollination Trial with Muskmelon cv. Athena

Objective: To quantify the effect of selected pollination strategies for muskmelon production in a mesotunnel, including effects on plant health, and fruit yield and quality.

Experimental Design: Each plot was 150 ft long, three rows wide with 7 ft centers, making the dimensions of a plot:  21 ft by 160 ft.  In this trial, three different treatments were compared (see below) and each treatment was replicated four times.

The three treatments for this trial were (Fig. 1):

• Full season: The exclusion netting (ExcludeNet®) was placed over the crop at transplanting and remained in place until harvest. A purchased bumblebee hive from Koppert Inc. was then inserted into the tunnel for pollination.
• Open ends: The exclusion netting was placed over the crop at transplanting, but during flowering, the short edges were opened so naturally occurring pollinators (honeybees, squash bees, etc.) could enter the tunnel.
• On/off/on: The exclusion netting was placed over the crop at transplanting but removed completely during flowering to provide naturally occurring pollinators access to the flowers, and then replaced.

The pollination period was three weeks within each treatment, after which the bees were taken out or the netting was reinstalled until harvest.

Results:

• BW incidence and progress was higher in the open ends treatment.
  • However, cucumber beetle populations were higher in the on/off/on treatment compared to the open ends and full season tunnels.
• A higher number of pollinators were observed in the on/off/on treatments.
• The number of marketable fruit and marketable fruit weight was higher in the on/off/on treatments compared to both open ends and full season treatments.
• The on/off/on treatment produced 77.9% and 74.5% more fruit than those with open ends or a bumblebee hive, respectively.

 

Take home message for pollination of muskmelon in mesotunnel production?

Our research over the past two years has indicated that using naturally occurring pollinators may be more effective and cost efficient than purchasing a bumblebee hive for pollination. However, depending on cucumber beetle populations, utilizing open ends or on/off/on approaches may be equally efficient. Higher marketable muskmelon yields were achieved by using the on/off/on strategy than the open ends or full season tunnel. However, in 2021, there was a higher incidence of both cucumber beetles and BW in the on/off/on treatment.

 

2022 IPM Trial with Acorn Squash cv. Table Ace and Muskmelon cv. Athena

Objective: To quantify the effect of mesotunnels and selected cover crops for weed management on major insect pests and diseases, and yield and quality of acorn squash and muskmelon.

Experimental Design: Each plot was 30 ft long with 3 beds and 7 ft centers, so an entire mesotunnel plot was 21 ft by 40 ft. This trial evaluated acorn squash and muskmelon grown with three types of weed suppression, in a full season mesotunnel or uncovered.

Each crop had four treatments (Fig. 2):

• Full season mesotunnel with landscape fabric between rows.
• Full season mesotunnel with annual ryegrass between rows.
• Full season mesotunnel with annual ryegrass/white clover mix between rows.
• Uncovered with landscape fabric between rows.

Each treatment with the full season mesotunnel had one commercial bumblebee hive placed in the center for pollination. Uncovered plots were subject to the activities of naturally occurring pollinators.

Results:

• CYVD incidence was 1,400% higher in the uncovered plots than the covered plots with landscape fabric.
• No CYVD was found in the covered rye/clover or rye only cover crop treatments.
• Insect pest populations (cucumber beetle, squash bug; eggs and adults, and aphid) were higher in the uncovered treatment.

Muskmelon

• ALS incidence was higher in muskmelon than acorn squash but was not affected by the treatment.
• Both cover crops treatments (rye only and rye/clover) were as effective for weed suppression as plots with landscape fabric.
• The percent of marketable fruit was 28.3% higher in covered plots with landscape fabric compared to uncovered plots.
• The number of marketable fruit was higher in covered plots with landscape fabric compared to those established with cover crops, which was not different than the uncovered.
• There was a higher incidence of soft fruit in the covered plots with landscape fabric suggesting this treatment may have enhanced the rate of ripening.
  • Whereas conversely, the incidence of unripe fruit was significantly higher in uncovered plots. 
• Average maximum temperatures in June, July and August were several degrees higher in the tunnel + fabric muskmelon plots compared to other treatments.

Acorn Squash

• Powdery mildew incidence was higher in acorn squash than muskmelon but was not affected by the treatment.

• CYVD incidence and squash bug populations were significantly higher in the uncovered squash treatments than all covered treatments.
  • Covered treatments had very low or no incidence of CYVD or squash bugs.
• Treatment did not have a significant effect on any yield components (number and/or weight of marketable and unmarketable fruit).
• The uncovered treatment had a higher incidence of fruit with holes or fruit that was sunburnt.
• Average temperature in June was four degrees higher in the tunnel + fabric than the tunnel + cover crop treatments, and nearly two degrees higher in the uncovered plots.
  • In June, average maximum temperatures were higher in the tunnel + fabric plots than the uncovered plots; but in August this trend was reversed. 

What does all this mean for integrated pest management in mesotunnel cucurbit production?!

The mesotunnel does provide an effective barrier between the insect pests and the crop.

For muskmelons, the cover crops were equally effective as the landscape fabric for weed suppression. However, for acorn squash, landscape fabric was beneficial for weed suppression, compared to the cover crops of ryegrass and ryegrass/white clover.

Next steps: We are working with our agricultural economists to compare the costs and benefits of these different cucurbit production systems. Stay tuned for more exciting updates!!