Palmer amaranth vs. common waterhemp
Author: Dr. Nathan Mueller – University of Nebraska Extension Agronomist
This is Dr. Nathan Mueller, your local agronomist with Nebraska Extension for Dodge and Washington counties. Over the past two weeks, farmers and agronomists have been contacting me for help in verifying if they have Palmer amaranth, a weed in their fields. So let’s cover key identifying plant parts of Palmer amaranth that are different from waterhemp, where we are finding Palmer amaranth in the area, and what we can do about weed infestations yet this year.
How can I tell if I have Palmer amaranth? Pictures help explain how to identify Palmer amaranth better than words do. So please visit our website at croptechcafe.org to view the pictures associated with this radio message. One of the key identifiers for Palmer amaranth is a long petiole. The petiole is the stem-like part that attaches to the leaf blade. First, detach the petiole and leaf blade from the main stem. Then fold the petiole back over the leaf blade. The petiole will be as long as or longer than the leaf blade. The petiole on waterhemp is shorter and is only about half the length of the lead blade (Figure 2). The leaf blade of Palmer amaranth itself is no as narrow as waterhemp. Another identifier is that the upper canopy or top leaves of Palmer amaranth is much denser and almost looks like a poinsettia whereas the canopy of waterhemp is much more open (Figure 3 and 4).
Where are we finding Palmer amaranth in this area? Reports this year of Palmer amaranth are coming from the Platte River Valley in Dodge County and localized areas within Cuming County. Palmer amaranth was also reported in Washington County last year. Therefore, we are dealing with a more widespread issue than we have in the past 4 to 5 years. Farmers have reported problems controlling Palmer amaranth with various herbicides, including glyphosate and PPO inhibitors.
What can we do yet this year (Recommendations from Purdue University) Hand weed severe infestations if possible yet this year before seed is produced. Also monitor and control Palmer amaranth along ditches and field edges to slow the spread of the local populations. Lastly, harvest heavily infested fields lasts so your combine doesn’t spread seed to your other fields I am planning on holding a meeting this next March for growers about how to best manage Palmer amaranth for the 2017 growing season.
To view pictures that help identify Palmer Amaranth (Figures 1 to 6), visit our local website at croptechcafe.org. Know your crop, know your tech, know your bottom line. This is Dr. Nathan Mueller, your local agronomist for Nebraska Extension on KTIC radio.