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1999 Integrated Pest Management Annual Report

Waterhemp Management Program

During the past five years, common and tall waterhemp have become a significant problem for Illinois corn and soybean producers.

Common and tall waterhemp (Amaranthus rudis and A. tuberculatus, respectively) are members of the Amaranth or pigweed family. Factors contributing to the increased severity of waterhemp infestations include selection for herbicide-resistant biotypes, changes in tillage and residue-management programs, and misidentification (and hence, improper or no control attempts). Accurate identification and herbicide selection are essential for management of these species.

Waterhemp plant
Accurate identification of waterhemp during early vegetative growth stages can be difficult.

Improper herbicide selection or misidentification of waterhemp may necessitate additional herbicide input costs for rescue treatments, in addition to the initial herbicide costs. The economic and environmental costs associated with improper herbicide selection and inaccurate identification are significant.

In Warren, Henderson, and Mercer counties in northwestern Illinois, 240,000 acres of soybeans are produced annually, with an average yield of 43 bushels per acre. Loss from waterhemp can range from 1 to 50 percent. Current estimates indicate that 30 to 50 percent of the soybean acres in these three counties are infested with waterhemp, with about 3,000 acres considered heavily infested. Soybean yield losses in the most heavily infested fields are estimated at 64,500 bushels. At a market price of $7 per bushel, the economic loss from waterhemp in these counties is estimated at $451,000.

With waterhemp infesting increasingly more acres, producers and others involved in agricultural pest management needed information about the biology of waterhemp species, as well as recommendations for management. To help meet this need, a research and demonstration program was conducted in 1997 at the Northwestern Illinois Research and Demonstration Center for 125 producers and agricultural suppliers. That same year, an IPM publication describing the identification, biology, ecology, and management of waterhemp in agronomic crops was published. This publication, Waterhemp Management in Agronomic Crops, was a collaboration of U of I Extension – IPM faculty and staff of the Department of Crop Sciences, the Department of Natural Resources and Environmental Sciences, and the USDA.

The genetic diversity of the waterhemp population contributes to a wide range of morphological characteristics.


Aaron Hager,,
Crop Sciences

Christy Sprague,,
Crop Sciences

Lloyd Wax,,
Crop Sciences

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