The Pigweed Species Identification Guide, February 2021 version, is now available thanks to the tireless work of Dave Bilyea, University of Guelph weed technician and Kristen Obeid, OMAFRA weed specialist – horticulture. Many excellent pictures were supplied by Christy Shropshire and Pete Smith, also technicians at the University of Guelph.

Ontario growers will appreciate the array of photos that show the distinguishing features between palmer amaranth, waterhemp, green and redroot pigweed. Identify these species at the cotyledon to two-leaf stage as well as their stems. 

A map of herbicide resistance for waterhemp in Ontario is provided.

If you are unsure what pigweed species you have or if you suspect herbicide resistance, contact Kristen Obeid for sampling protocols, collection kits and the procedure for sample submissions to Harvest Genomics. Genetic testing is available to determine what pigweed species you have and for resistance. Redroot and green pigweed can be tested for resistance to herbicide groups 2, 5 and 7. Waterhemp can be tested for resistance to herbicide groups 2, 5, 9 and 14.

Contact: Kristen.Obeid@ontario.ca

Source: Kristen Obeid, OMAFRA weed specialist- horticulture, February 9, 2021