High tunnels can boost crop yield by allowing for earlier planting and later harvesting of cold-sensitive crops, but new research shows high tunnels may also be a boon to insect pests, as well. (Photo credit: Flickr/U.S. Department of Agriculture)

High tunnels are a common sight in farm fields in temperate zones, where growers use them to lengthen the growing season of cold-sensitive crops. Also known as hoop houses, the large metal frames covered with plastic sheeting keep plants warmer as ambient temperatures begin to fall.

Conventional wisdom holds that high tunnels shield plants from insect pests, as well, but new research by entomologists at Purdue University shows otherwise. In a two-year study comparing plants in high tunnels versus plants in open field plots, they found greater presence of pests inside the high tunnels than out.

The crops and associated pests studied were tomatoes and hornworms; broccoli and cabbage loopers, imported cabbageworms, and diamondback moths; and cucumber and cucumber beetles. Senior author of the study Ricky Foster, Ph.D., professor of entomology at Purdue, says the results were especially remarkable for tomatoes.

“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 says. “There was just nothing green left on the plants. There were just stems hanging on them.”

A study of pest presence in crops protected by high tunnels compared to crops in open fields showed increased levels of pests, such as the tomato hornworm (Manduca quinquemaculata), inside the high tunnels. (Photo credit: Sarah Thompson, Purdue University)

The study did not determine how insects entered the high tunnels, but Foster says a simple explanation is likely that the enter when the sides of the tunnels are opened for ventilation on warmer days. “We have to ventilate the tunnels by rolling up the sides, and that basically opens it up for any type of insect that wants to come in,” Foster says.

Lead author Laura Ingwell, Ph.D., a postdoctoral researcher at Purdue, is conducting studies on screens of various pore size for their ability to allow ventilation but exclude pest insects. Her work is funded by a grant from the U.S. Department of Agriculture’s Agriculture and Food Research Initiative.