Integrated Cropping Systems Team Addresses Management of Pesticide Resistance

AMES, Iowa -- There is much to consider when making management decisions in production agriculture – including the pesticide resistance of target pests (weed, insects, plant pathogens and nematodes). The complexity of crop production decision-making is escalated by frogeye leaf spot, the arrival of Palmer amaranth, and corn rootworm resistance – a few of the issues that have Iowa farmers concerned about pesticide resistance.

Members of the Iowa State University research and extension crops team will be at the Farm Progress Show talking to visitors about current and potential resistance issues and related management practices. The team includes agronomists, entomologists, plant pathologists and microbiologists, weed scientists and a climatologist.


Erin Hodgson, extension entomologist and associate professor of entomology, is a crops team leader and describes resistance as “the decreased susceptibility of a pest to a management strategy.” Often, resistance is associated with pesticides but it could include cultural control (e.g., crop rotation) and host plant resistance (e.g., Bt for insects).

“When it comes to insects, they are always trying to evolve to be more competitive,” said Hodgson. “Eventually, insects will overcome our standard management tactics. Some, like western corn rootworm, just do it faster than most.”


Weeds with resistance to herbicides were first found in the 1950s. Now that Palmer amaranth has arrived in five Iowa counties – along with its history of resistance in other states – herbicide resistant weeds are getting more attention. Bob Hartzler, agronomy professor and extension weed scientist with Iowa State University, says the solution to managing the situation is simple – farmers must stop doing what they are doing (referring to spraying glyphosate on fields planted with seeds genetically engineered to tolerate the chemical) and take different actions.

“Start deploying more diverse weed management strategies that incorporate some combination of crop rotation, cover crops, manual tillage, and a broader range of herbicides less dependent on glyphosate,” said Hartzler.

Diseases and Integrated Pest Management

Daren Mueller, extension soybean pathologist and coordinator of the Integrated Pest Management program at Iowa State, says pesticide resistance results from using the same pesticide repeatedly. When resistant weeds, insects and fungi are present, Mueller says a biotype of an organism has survived exposure to a pesticide that would normally kill an individual of that species. Resistance can be managed several ways so that pesticides remain a useful way of controlling pest organisms now and in the future.

“Only apply pesticides when needed – scout fields to determine pest populations and only use pesticides when thresholds are met. Then follow label directions,” Mueller said. “Rotate types of pesticides during the year and from year to year. And use alternative management options such as production practices, natural enemies, crop resistance and crop rotation.”

The Iowa State crops team and IPM program provide up-to-date resources and information through trainings, field days, demonstration sites, online newsletter and publications. The team publishes articles in the Integrated Crop Management newsletter at containing the latest information available. Scouting and pest identification guides created by team members are available from the Extension Online Store at

Visit the Iowa State University tent at the Farm Progress Show Aug. 26-28 to meet Iowa State researchers and specialists working in the area of pest resistance.