Vegetable Pest Populations Can Soar in High Tunnels, Study Shows

Vegetable Pest Populations Can Soar in High Tunnels, Study Shows

Researchers saw significant increases in the number of tomato hornworms (pictured here) in high tunnels. The pests caused severe damage to tomato plants. Photo by MTSO fan

Although high tunnels are widely used by vegetable growers, surprisingly little research has been conducted to test their performance. Purdue University researcher Ricky Foster and his team set out to change that with a study focusing on pest levels.

“Many growers using high tunnels, or hoop houses, can extend their growing season significantly,” says Brian Wallheimer, who wrote the article profiling the study for Purdue. “But an assumption about how the enclosures guard against insect protection isn’t backed up by this study. Rather than keeping insects out, the high tunnels seem to keep pests in, sometimes with significant damage associated.”

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Here are Some Details of the Study

  • Crops Tested: Three different crops and the pests that are most often associated with them: Tomatoes and hornworms; broccoli and the cabbage looper, imported cabbageworm and diamondback moth; and cucumber and the cucumber beetle.
  • Length of Study: Two years
  • Results in Brief: Pest populations on the whole were higher than populations in adjacent fields:
    • Tomato Hornworm was a particular problem. “In field situations, hornworms are kind of an anomaly. They’re there, but not in great numbers. We found that in high tunnels, they just exploded,” Foster, who is a Purdue professor of entomology told Wallheimer. “There was just nothing green left on the plants. There were just stems hanging on them.”
    • The Likely Culprit of High Pest Levels? Ventilation. Researchers raised the side coverings on warm days to prevent temperatures reaching more than 120 degrees. That allowed pests to enter, and then they were often trapped when the sides were lowered or when pests wanted to fly up and were stopped by the top of the high tunnel structure.

 

Possible Counter Measures

Laura L. Ingwell, a postdoctoral researcher at Purdue, is conducting related research that is evaluating ways to counter the pest pressure.

She is testing ways to screen crops without sacrificing ventilation, evaluating three different screens of varying pore size.

She is also seeing if growing floral crops — zinnia and gomphrena — among vegetables has an impact on pest populations. Wallheimer reports she’s seeing good results on this front.

“We saw a higher diversity and abundance of predators and less pest outbreaks on the focal produce crops,” Ingwell says. “The flowers offer alternative food for a lot of the beneficial insects. They’ll feed on the pest insects, but they also need pollen and nectar for their diets.”

The study results can be seen in the trade journal, Pest Management Science.



 

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Gregory Lang says:

Ron Goldy at Michigan State found similar results with hornworms in high tunnels about 10 years ago and eventually concluded that hornworm moths were active at night and therefore were not influenced by changes in light spectra under plastic covers, but flight of the parasitic wasp for hornworm occurred during the day and the change in light spectra tended to inhibit wasp flight into tunnels (possibly similarly to how honeybee navigation is disrupted under many plastics that alter light spectra).