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Identification of Palmer amaranth and waterhemp <br />Proper identification is an important component of managing Palmer amaranth <br />and waterhemp. Two common weeds that are mistaken for Palmer amaranth and <br />waterhemp are redroot pigweed and Powell amaranth. Here are some tips to identify <br />these four weeds from the seedling stage through plant maturity. <br /> <br />Palmer amaranth <br />(Amaranthus <br />palmeri) <br />Waterhemp <br />(Amaranthus <br />tuberculatus) <br />Redroot pigweed <br />(Amaranthus <br />retroflexus) <br />Powell amaranth <br />(Amaranthus <br />powellii) <br />Stems Smooth, no hair Smooth, no hair Short, dense <br />hairs <br />Short, dense to <br />sparse hairs <br />Petiole length Long, as long or <br />longer than leaf <br />blade <br />Short Typically short, <br />can be long on <br />mature plants <br />Typically short, <br />can be long on <br />mature plants <br />Inflorescence (Seed head) <br />Open, <br />unbranched, <br />very long <br />Male are <br />smooth, female <br />are prickly <br />Open, <br />unbranched <br />Male and female <br />are smooth <br />Compact, <br />branched, 1-2" <br />Smooth to <br />rough, but not <br />prickly <br />Compact, <br />branched, 4-8" <br />Smooth to <br />rough, but not <br />prickly <br />Bracts Spiny bracts on <br />female plants <br />No spiny bracts No spiny bracts No spiny bracts <br />Reproductive Dioecious <br />(separate male <br />and female <br />plants) <br />Dioecious <br />(separate male <br />and female <br />plants) <br />Monoecious <br />(male and <br />female flowers <br />on same plant) <br />Monoecious <br />(male and <br />female flowers <br />on same plant) <br />W1916 <br />Identification, Biology and Control of <br />Palmer Amaranth and Waterhemp <br />in North Dakota <br />North Dakota State University <br />Fargo, North Dakota <br />May 2019 <br />Joe Ikley, NDSU Extension Weed Specialist <br />Brian Jenks, Weed Scientist, North Central Research Extension Center <br />Waterhemp and Palmer <br />amaranth are two pigweed <br />species that now are found in North <br />Dakota and pose a serious threat <br />to crop production. Both of these <br />weeds have populations in other <br />parts of the U.S. that have become <br />resistant to nearly every herbicide <br />mode of action used in crop <br />production. <br />This publication will explain how <br />the biology of waterhemp and <br />Palmer amaranth, in addition to <br />herbicide resistance, make them <br />more difficult to control than redroot <br />pigweed or Powell amaranth. <br />North Dakota farmers have dealt <br />with pigweed (Amaranthus) for <br />most of our farming history. Recent <br />research has found that some <br />populations of redroot pigweed <br />are resistant to acetolactate <br />synthase (ALS)-inhibiting (Group 2) <br />herbicides in the state. <br />In the 1990s, waterhemp <br />(Amaranthus tuberculatus) was <br />identified in fields in the Red River <br />Valley, and it has been rapidly <br />spreading in the eastern half of <br />North Dakota over the last decade. <br />Palmer amaranth (Amaranthus <br />palmeri) was first identified in <br />North Dakota in 2018. This weed <br />has been one of the most difficult <br />to control weeds in the southern <br />United States for more than two <br />decades. Populations found in <br />North Dakota suggest that this plant <br />can adapt and become competitive <br />in the northern Great Plains as well.