Ambitious Strategies to Control Pests and Diseases in Organic Agriculture • News Service • Iowa State University


Mesotunnels, like the ones pictured here, are made of nylon mesh fabric suspended from hoops placed about 42 inches above the ground. The management technique prevents pests from attacking crops. Photo courtesy of Mark Gleason. Bigger picture.

AMES, Iowa – Fruit and vegetable growers adopting organic farming practices are forgoing some of the tools commonly used by conventional farmers to control pests and diseases, but Iowa State University researchers are experimenting with new methods that could offer new options to organic producers.

Researchers received a $2 million grant from the U.S. Department of Agriculture‘s National Institute of Food and Agriculture to test two promising biological methods to help cucurbits, a group of plants that includes the melons, squash and cucumbers, to fight insects that carry bacterial diseases. The researchers will team up with scientists from Cornell University and the University of Kentucky to examine the physical barriers that protect plants from unwanted insects and biological control measures.

“Organic growers encounter many pests and diseases that are difficult to manage with biological tools,” said Mark Gleason, professor of plant pathology and microbiology at ISU and member of the research team. “Our goal is to identify innovative ways to address these issues that also improve sustainability.”

Much of the research will focus on cucumber beetles, squash bugs and other insect pests that target cucurbits and often carry disease-causing bacteria. Gleason said cucumber beetles and squash bugs can devastate organic crops. Growers can use organic pesticides, but those that are available are not as effective as conventional pesticides.


Test a new tunnel strategy

Gleason and his research team will study the effectiveness of mesotunnels, or physical barriers consisting of nylon mesh fabric suspended from hoops placed about 42 inches above the ground, to prevent pests from attacking crops. . Each mesotunnel will span three rows, and each row of experiments will span 200 feet.

Mesotunnels are similar to a management tool known as low tunnels, which are physical barriers installed approximately 18 inches above crops. Low tunnels, however, do not allow beneficial insects to pollinate plants, a necessary step in crop production, so screens must be removed when plants begin to flower to allow pollination.

“Cucurbit crops need bees to pollinate them, so with low tunnels, you have to remove the row covers to let the bees in,” Gleason said. “You can have protection for a few weeks, but then the plants get hammered when the cover is removed.”

The new strategy – mesotunnels – can stay in place and protect crops throughout the growing season, he said. The experiments’ mesotunnels will be outfitted with bumblebee boxes to provide pollination, Gleason said. Mesotunnels have worked well in Iowa on a smaller scale, and the new grant will allow researchers to test the method at a scale approaching that of commercial growers.

The researchers will also test several weed control strategies in conjunction with the mesotunnels, Gleason said. These methods include laying down crop debris and seeding “living mulch” or plant species such as clover and rye.

The grant also calls on researchers to evaluate potential biological control methods that could help organic farmers combat disease. These biological control methods would require growers to introduce biological agents, such as bacteria and viruses, that suppress bacterial diseases in their crops. Researchers will look at bacteria and fungi that induce disease resistance in cucurbits, as well as viruses that attack disease-causing bacteria.

“It’s ambitious, but it fits well into organic farming,” Gleason said. “These biological control organisms are harmless to the environment and can combine well with other disease control tactics such as mesotunnels.”

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