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Update on Early Emerging Waterhemp (05/14/20)

Last week, Dr. Tom Peter’s wrote an article about observations of waterhemp emergence in early May in North Dakota and Minnesota.

Last week, Dr. Tom Peter’s wrote an article about observations of waterhemp emergence in early May in North Dakota and Minnesota. We have received subsequent reports and pictures confirming waterhemp emergence as far north as Pembina County. One question many have asked over the past week is: will these waterhemp survive the overnight subfreezing temperatures from May 7th through 12th. I scouted the field in Cass County where emergence was observed on May 1st and the short answer is yes, waterhemp made it through the cold spell. Some plants did not survive the weather and many plants had lost their green color, but will likely start growing again once warmer temperatures arrive. Several plants also seemed unaffected by the cold temperatures. I was not able to find plants that had produced a true leaf yet, indicating that the waterhemp had not actively grown during a 12-day window since emergence on May 1st.

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The fact that early emerging waterhemp survived our cold spell has implications on management moving forward. If fields have not been planted, these plants can be controlled through tillage or a burndown application. Herbicides will be more effective once these plants start actively growing as warmer temperatures arrive. If waterhemp is present in fields with emerged crops, we need to continue to scout these fields and make sure that postemergence applications are applied in a timely fashion. Lastly, it is important to remember that there will be many more flushes of waterhemp throughout the year and the war on waterhemp in 2020 is just getting started.

 

Joe Ikley

Extension Weed Specialist

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