Most areas of the Corn Belt assume that every population of waterhemp is already resistant to ALS herbicides, which developed in the 1990s. Waterhemp can adapt quickly to repeated control measures and, in some states, it has been found resistant to multiple modes of action.
Scientific name: Amaranthus tuberculatus
Germination period: April – September
Height: Up to 12 feet
Most famous for: Adapting to soybean herbicides used throughout the 1990s, evolving herbicides resistance and cross-breeding with other Amaranthus species
Seed production: Up to .5 million per plant
Common habitats: Ditches, fencerows, corn and soybean fields, wastelands
Potential yield loss: Corn – 30 plants/ft2 can reduce yield 15% by the time waterhemp was 6 inches tall*
Soybeans – 20 plants/ft2 can reduce yield 44% in 30-inch rows*
Modes of action with confirmend resistance: ALS inhibitors, glyphosate, photosystem II (PSI) inhibitors, PPO inhibitors
*2004 university research, published by Purdue University.
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