Pigweed identification

Developed by Lynn M. Sosnoskie, Assistant Professor, Specialty Crop Weed Science Lab, Cornell AgriTech
Horticulture Section, School of Integrative Plant Science, College of Agriculture and Life Sciences, Cornell Univ.
Email: lms438 [at] cornell.edu (lms438[at]cornell[dot]edu) | Twitter: @vegfruitweedsci | Instagram: @specialtycropweedscience

Funding generously provided by the New York Corn & Soybean Growers Association (NYCSGA - 2021 Corn Research and Education Grant)

How to identify pigweeds
Palmer Amaranth (Amaranthus palmeri)
Waterhemp (Amaranthus tuberculatus)
Powell Amaranth (Amaranthus powellii)
Redroot Pigweed (Amaranthus retroflexus)
Smooth Pigweed (Amaranthus hybridus)
Purple Pigweed (Amaranthus blitum)
Comparison images - More side-by-side images to help you distinguish species.
Herbicide resistance

Printer-friendly .pdf versions of pigweed ID content:

Pigweed Identification: A Quick Guide for Five Common Species in NY - Letter-sized booklet
Pigweed Identification: A Quick Guide for Five Common Species in NY - 16:9 Powerpoint slides
How to Identify Palmer Amaranth and How to Identify Waterhemp - Two one-pager, letter-sized factsheets.
Amaranthus blitum or Purple Pigweed: A New(er) Pigweed in Town - Two one-pager, letter-sized factsheet

Email: lms438 [at] cornell.edu (lms438[at]cornell[dot]edu) to inquire about additional PowerPoint slides.

Why ID pigweeds?

Competition and yield loss

Pigweeds are some of the most commonly occurring and troublesome weeds that US growers encounter. Several pigweed species can grow very quickly, often overtaking the crops that they emerge with (like Palmer amaranth on left).

Why pigweeds?

Seed production and seedbank growth

Pigweeds can produce a lot of seed. Under optimal growing conditions, these species can produce tens to hundreds of thousands of seeds; female Palmer amaranth plants have been reported as producing up to a million seed. This leads to the development of large seedbanks.

Why pigweeds?

Herbicide resistance

As of December 2021, there are 162 confirmed cases of resistance across all pigweed species, herbicides, and states in the US. 40 of these reports detail resistances to multiple herbicide groups within a single plant population (weedscience.org).