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Waterhemp (Amaranthus rudis)

Crop Impacts: Soybeans, corn and peanuts

Waterhemp 1

About Waterhemp:

Waterhemp is a summer annual weed that appears in the later parts of the growing season. It is fast growing with a high seed production and a long germination period. Waterhemp is a dioecious weed, which means individual plants are either producing male flowers called staminate flower, or female flowers called pistillate flower. This weed is poisonous for cattle, horses, sheep and goats when ingested.

Family: Pigweed family (Amaranthaceae)

Waterhemp 2

Waterhemp Scouting and Prevention:

Waterhemp is a weed that varies drastically in height between 2 to 8 feet tall with a ridged or rounded stem that appears green to pinkish red. It has many branches, which are larger at the bottom and smaller at the top. This plant has alternating green leaves that can reach about 6 inches long and 1.5 inches across. Waterhemp also produces narrow spiked flowers that can grow up to 1 foot tall. This weed produces male plants, or staminate flowers that have 5 sepals and 5 stamens. Along with a female Waterhemp, or pistillate flowers that typically have 1 sepal and an ovary.

Common locations

  • - Is where there is partial or full sun
  • - Wet, moist conditions
  • - Fertile soil that has clay or loam in it
  • - Soybean fields
  • - Corn fields
  • - Peanut fields
  • - Wet pastures and fields

Waterhemp Control:

The best way to deal with Waterhemp in fields, specifically corn and soybean fields, is to combine cultural control practices such as tillage and cultivation along with chemical control methods. This would be the application of soils-applied herbicides and then finishing with post-emergent herbicides

Chemical Control

Soil-applied herbicide is the first chemical control step in protecting soybeans and corn from Waterhemp. Time of application is very important. If applied too early, the control of Waterhemp declines. Waterhemp is a late emerging weed, meaning that soil-applied herbicides should be applied 1 to 2 weeks before planting. The only time you may want to consider applying immediately before planting, is when there is a significant Waterhemp problem.

Post-emergent herbicide more often than not is applied as late as possible in the growing season to make sure there are as many weeds actively growing as there can be. By the time post-emergent herbicide is applied, there are many sizes of Waterhemp due to the fact that they have a long germination process. The problem with applying the herbicide late is that the smaller Waterhemp weeds are protected by the canopy of the larger plants. To make sure every plant has a uniformed coverage, have an application pressure of 40 to 50 pounds per square inch with 20 gallons per acre of spray volume.

Suggested herbicide brands that can deal with Waterhemp in agricultural fields: Cobra herbicide, Fierce herbicide, Gangster herbicide and Phoenix herbicide. If Waterhemp starts to show in your gardens and/or turf, BroadStar herbicide, Playload herbicide and SureGuard herbicide work effectively.

Latin / Alternative Waterhemp names:

  • - Amaranthus rudis

Additional Waterhemp Resources

http://www.valent.com/pests/waterhemp.cfm

http://www.omafra.gov.on.ca/english/livestock/dairy/facts/poisonousweeds.htm

http://www.illinoiswildflowers.info/weeds/plants/water_hemp.htm

http://bulletin.ipm.illinois.edu/pastpest/articles/200105l.html