Redroot pigweed is a summer annual that is native and present in all states of the continental US. Herbicide resistant populations are present in 20 states stretching as far north as Maine. Because of widespread resistance to Group 2 herbicides (ALS inhibitors) and Group 5 (triazines), producers dealing with redroot pigweed should diversify the herbicide sites of action in tank mixes and between seasons. Avoiding use of the same herbicide site of action two years in a row will help decrease the chance of populations developing in the field that are resistant to that SOA.
Redroot pigweed can be challenging to distinguish from other pigweeds, but identification is important for proper management. Redroot pigweed should be carefully distinguished from Palmer Amaranth and waterhemp, which are multiple-resistant pigweeds of high concern and are spreading in many US states. If unsure whether a pigweed is redroot or another pigweed, please contact us or your local extension weed specialist.
Herbicide resistant populations:
- Group 2
- Group 5
- Group 2 + 5
- Group 5 + 7
Locations of resistant populations:
Arkansas, Colorado, Connecticut, Delaware, Idaho, Indiana, Kansas, Maine, Maryland, Michigan, Minnesota, Nebraska, New Hampshire, North Dakota, Oregon, Pennsylvania, Vermont, Virginia, Washington, West Virginia
PM1786 (1) – Pigweed Identification Manual – Iowa State University