Palmer amaranth
Amaranthus palmeri S. Wats.

Overview

Appearance

Amaranthus palmeri is native to to the desert regions of the southwest United States and northern Mexico. It has become one of the most widespread, troublesome, and economically damaging agronomic weeds in the southeastern U.S. A. palmeri is an erect, branching, summer annual that usually grows from 6-8 ft (1.8-2.4 m) tall.

Foliage

The petiole is longer than the leaf. Petiole length is a key identifying characteristic. The alternate leaves are ovate to diamond shaped and some leaves will have a white watermark shaped like a chevron or V.

Flowers

Male and female flowers are borne on separate plants, and the small inconspicuous flowers are clustered tightly in linear or sparingly branched terminal spikes up to 18 in (45.7 cm) long.

Fruit

The seeds are shiny and dark reddish brown to brown. They are about 0.04-0.05 in (1-1.2 mm) in diameter.

Ecological Threat

A. palmeri thrives in hot weather, is tolerate of drought, and responds quickly to high levels of available nutrients. It competes aggressively against warm season crops, and is a prolific seed producer. A. palmeri populations have developed resistance to multiple herbicide modes of action, including ALS inhibitors, triazines, HPPD inhibitors, dinitroanilines, and glyphosate. This plant can have a greatly extended emergence period. Due to this extended emergence period producers must spend additional time and money to manage it.

Selected Images

Maps

Invasive Listing Sources

• Delaware Noxious Weeds
• Delaware Regulations for Noxious Weed Control
• Minnesota Noxious Weeds
• North Dakota Noxious Weeds
• Ohio Noxious Weeds
• Pennsylvania Department of Conservation and Natural Resources Invasive Plants
• Pennsylvania Noxious Weeds
• Pennsylvania Regulations for Controlled Plants and Noxious Weeds

References