Boise, Idaho
June 16, 2005

We know that it happens with pharmaceuticals: one chemical will interact with another, interfering with its therapeutic effects or even putting our health at risk. Scientists also know that it happens with agricultural chemicals used in such crops as corn and soybeans: interactions can make these crops more prone to herbicide injury or insect damage.
 

This year, scientists at the University of Idaho College of Agricultural and Life Sciences are launching a two-year study to find out whether-and how-insecticides, fungicides and herbicides interact in Idaho potato fields. "With all of the new pesticides that are systemic and actually move into the plant, we need to find out whether one pesticide interferes with or interacts with another," says project leader Mike Thornton, plant physiologist and superintendent of the Southwest Idaho Research and Extension Center at Parma. "That may explain some of the problems that growers are seeing in the field."
 

At Aberdeen, weed scientist Pamela Hutchinson says one possible interaction is that an herbicide applied after planting may interfere with the crop's uptake of a long-acting pre-plant insecticide. "Then, for example, the crop wouldn't be protected against an insect like Colorado potato beetle." Or, an herbicide that potato plants typically disarm metabolically may damage the crop as well as the intended weed, because an insecticide interferes with the crop's ability to break down the herbicide.
 

Not only will Hutchinson and Thornton examine every possible combination of four insecticides and two herbicides in the field, but Hutchinson will also grow potatoes and the related weed hairy nightshade in the greenhouse. After exposing them to various crop-protection products, she'll use radiolabeling to trace how much of each compound is taken up by the crop and the weed and ultimately determine whether the herbicides and insecticides interfere with one another's uptake. 
 

In addition, the UI scientific team-which also includes potato pathologist Jeff Miller of Aberdeen and nematologist Saad Hafez of Parma-will measure the incidence and severity of Rhizoctonia stem and stolon canker to see if any combinations of chemicals lead to more disease. Research in soybeans suggests that plant injury caused by pesticide interactions could be making that crop more prone to some diseases. The team will also determine whether combinations of pesticides and fungicides reduce the ability of beneficial nematodes to control plant-damaging nematodes. In addition, the agricultural scientists will also evaluate the effects of these compounds-both separately and in combination-on soil microbial activity and other measures of soil health.
 

A preliminary study that Thornton conducted in potatoes last year showed increased seed decay when a nematicide was applied at planting-and even more seed decay when an in-furrow fungicide was applied at the same time. "It may be that we are knocking down the populations of beneficial microorganisms in the soil that normally help keep seed decay in check," he says.
 

"It's really an interesting study," says Thornton. "I'm excited about it."
 

"What it may teach us is that even more of our research needs to be done in an interdisciplinary manner," says Hutchinson. "Crop-protection products are usually studied and developed separately, but growers use them together in the field."
 

The research is being funded by the USDA Agricultural Research Service's Potato Research Program and the Idaho Potato Commission. Hutchinson and the other researchers hope it will lead to new strategies for understanding these and many other interactions that affect pest management in potato-production systems.