Monika Chandler, Minnesota Department of Agriculture
November’s Weed of the Month is Palmer amaranth (Amaranthus palmeri). This fast growing weed has developed resistance to multiple herbicide modes of action so it is difficult to control. Palmer amaranth produces a lot of seed, up to 250,000 per plant, and is highly competitive. It spreads quickly and can cause extensive crop losses including corn and soybean production.
Palmer amaranth is native to the arid southwestern United States and northwestern Mexico. It was accidentally introduced to the southeastern United States and became the most troublesome weed in cotton production. It developed resistance to many herbicides modes of action and spread to row crop fields in much of the eastern half of the country. This dreaded weed was discovered in Minnesota in 2016.
Palmer amaranth can be distinguished from closely related waterhemp and other pigweeds by a long petiole length and very tall flower and seed spikes. Unlike other pigweeds, Palmer amaranth petioles are often longer than the leaf blades. A petiole attaches a leaf to a stem. The flowering spike is much longer than that of other pigweeds. Leaves of some Palmer amaranth plants have a whitish V-shaped mark on them. Palmer amaranth is a summer annual that commonly reaches heights of 6-8 feet but can reach 10 feet.
If you find this plant, please report immediately by calling the Arrest the Pest at 888-545-6684 or emailing arrest.the.pest@state.mn.us.
Source: Minnesota Department of Agriculture