Amaranthus palmeri

Scientific Name Amaranthus palmeri - S.Watson.
Common Names English : Palmer's Amaranth, Palmer Pigweed, Carelessweed; German: Fuchsschwanz-Amarant, Palmer Amarant; Spanish: Quelite de aguas, quelite; French: Amarante de Palmer
Description An erect summer annual that may reach 2 m (6.56 ft) in height. Taproot often reddish in color.

Descriptions

Characteristic Features

Dense, compact terminal panicles and relatively tall plants with alternately arranged leaves with petioles that are longer than the leaves.

Young Plant

Stems below the cotyledons (hypocotyls) are without hairs (glabrous) but sometimes slightly hairy, and often red in color. First true leaves are alternate, ovate in shape, and slightly notched at the tip of the leaf blade (apex).

Cotyledons

Narrow (10 to 12 mm; 0.39 - 0.47 inch) long and green to reddish on the upper surface. Lower surfaces of cotyledons have a reddish tint.

Stems

One central stem occurs from which several lateral branches arise.

Leaves

Alternate, without hairs (glabrous), and lance-shaped or egg-shaped in outline. Leaves are 5 to 20 cm (1.97 - 7.87 inch) long and 2-6 cm (0.78 - 2.36 inch) wide with prominent white veins on the undersurface. Leaves occur on relatively long petioles.

Propagatio Organs

Flowers

The plant is diecious. Pollen travels from male to female plants by wind. Small, green, inconspicuous flowers are produced in dense, compact, terminal panicles that are from 15 - 45 cm (5.9 - 17.7 inch) in length. Smaller lateral inflorescences also occur between the stem and the leaf petioles (leaf axils). Male and female flowers occur on separate plants. Each terminal panicle contains many densely packed branched spikes that have bracts that are 3 to 6 mm (0.12 - 0.24 inch) long.

Flowering Period

June - November.

Fruit

A single seeded utricle, 2 mm (0.078 inch) in length and wrinkled when dry. Each utricle splits open in the middle to expose the seed.

Seeds

Single glossy black to dark brown, 1 to 1.2 mm (0.039 - 0.047 inch) long. Main germination period is in spring.

Viability Of Seeds

Tens of thousands to hundreds of thousands persistent seeds per plant.

Propagation

By seeds.

Occurrence

Habitat

Open areas with full sun and disturbed areas, agricultural fields.

Soil

Disturbed soils.

Additional Crop Information

Corn, peanuts.

Agricultural Importance

Palmer amaranth is among the five most troublesome weeds in cotton, peanut, and soybean throughout the Southeast US and may be considered the most aggressive of the pigweed species. The acquisition of resistance of many biotypes to various herbicides with different modes of action , such as glyphosate, dinitroanilines, ALS- inhibitors and others limits the options for selective chemical control. The separation of male and female organs on separate plants in the diecious manner resulted in the rapid spreading of herbicide resistance over extend geographical areas within a short period of time.

Besides yield reduction of all infested crops A. palmeri shows competitive interference on cotton development, and fiber properties.

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