Mesotunnels are a new strategy for producing organic cucurbit crops in the Midwest. These fabric-covered tunnels protect the cucurbit crops from damage caused by pest insects and the diseases they spread.

However, there is a learning curve associated with using mesotunnels for cucurbit crops. Based on several years of our field experience in Iowa, using these tunnels for organic production of acorn squash, here are some tips for commercial cucurbit growers in the form of do’s and don’ts:

Do’s:

• Protect your seedlings before transplanting. This can be done by wrapping the flats in the nylon-mesh fabric (brand names are ProtekNet and ExcludeNet) used for the tunnels. This fabric will prevent insect-pest entry but will not overheat the seedlings.
• Install the mesotunnels on the same day as transplanting. Young transplants are highly attractive to cucumber beetles, so must be protected right away.
• Scout for insect pests and diseases inside the nets by looking through the nets regularly (once a week at a minimum). When counts of pest insects (for example, cucumber beetles or squash bugs) per plant exceed established thresholds (which are readily available from Extension resources), apply one or more OMRI-registered insecticides.

Figure 1. Left: Squash bug adult on a mesotunnel. Right: Squash bug eggs on a rolled ProtekNet.

• Mesotunnel fabric is often removed for a couple of weeks during bloom, to allow bees to pollinate the crop. If squash bugs outside the nets are very numerous before opening the mesotunnels, applying an insecticide spray before removing the nets may reduce infestation of the crop. Since organic insecticides are not very effective against squash bug adults, an additional option includes manual control. Adult squash bugs can be picked off the nets and dropped into a container filled with soapy water.
• If pesticide sprays are needed, spray them when bees are not present in the crop. If you are spraying a mesotunnel system that has purchased bumble bee hives inside, close the hive entrance the day before spraying to avoid pesticide injury to the bees, then re-open it several hours after spraying.
• The most effective time to apply the first insecticide spray for squash bugs is during the peak of nymph hatching.
• Control weeds that can cause further pest problems. For instance, waterhemp may attract aphids, which can then invade your crop. If you have aphids inside the mesotunnels, you can introduce purchased lady beetles into the tunnels as predators. Alternatively, if you are opening the mesotunnels to allow pollination to occur, natural enemies may help to control the aphids.
• If you mow living mulches in the alleys between the rows, move the runners of the squash plants beforehand in order to avoid damaging them.

Figure 2. Left: Waterhemp infested by aphids inside a mesotunnel. Right: Ladybug excluded by the mesotunnel net.

Don’ts:

• Don’t keep materials in the fields and field edges that could harbor overwintering squash bugs. Pallets, sandbags, and plant debris can shelter squash bugs and ensure their survival until the next growing season.
• Don’t make holes in the nylon-mesh fabric. If you are opening the ends of the nets to allow pollinators to enter the mesotunnels during bloom, tie the ends open using monofilament fishing line or fine-gauge wire to avoid poking holes in the fabric. If you are removing the nets at bloom, be careful the nets don’t get pulled forcibly from the sandbags or any other objects; they may rip.
• Don’t neglect to repair holes before you use the nets again. Repair the holes during winter, or before you install them in the field. Monofilament fishing line makes a suitable material for repairing holes in the fabric. Nets are not difficult to repair, but it can be time-consuming to repair large nets if holes are numerous. See this video for further information on repairing nylon-mesh nets.

Using mesotunnels for cucurbit production can help increase cucurbit crop yields, and potentially improve profitability. But like any other new technology, there is a learning curve associated with their use. You may develop your own list of do’s and don’ts list when using mesotunnels; this list may differ depending on your location, production practices, and marketing strategy.