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Pigweed Identification using Flowering Structure (08/16/18)

Pigweed (Amaranthus species) are in full flower. I thought it might be a good idea to refresh weed identification skills based on characteristics of the flowering structure.

Pigweed Identification using Flowering Structure

Pigweed (Amaranthus species) are in full flower. I thought it might be a good idea to refresh weed identification skills based on characteristics of the flowering structure.

Redroot pigweed. Flowering structure is highly branched with male and female flowers on the same plant. Branches of flowering structure usual are very compact, usually less than 2-inches long and thicker than a pencil. Redroot pigweed is very common across Minnesota and North Dakota.

 

Powell amaranth.

Flowering structure is branched, but less than redroot pigweed. Branches of the flowering structure are usually 4 to 8 inches long and thicker than a pencil. Male and female flowers are on the same plant. At first glance, Powell amaranth will remind you of those pictures of Palmer amaranth from other states. Powell amaranth is common in North Dakota and northwest and north central Minnesota but less common in southern and west central Minnesota.

Waterhemp.

Flowering structure are open and located near the top of the plant and at the tips of branches. There are male and female waterhemp plants. Males shed pollen while females produce seed. Male plants tend to have a flowering structure with a dominant central branch while female plants are highly branched with branches of proportional size. Waterhemp is abundant in North Dakota, especially east of US281.

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Palmer amaranth.

Like waterhemp, each plant is either male or female. The male flowering structure feels soft and sheds pollen, while female flowering structure feels prickly and contains seed. The branches of Palmer amaranth are very long, often up to 24 inches in length. We currently have not identified Palmer amaranth in North Dakota

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Tom Peters

 Extension Sugarbeet Agronomist

NDSU & U of MN

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