Brazos County Herbarium

Brazos County Horticulture Extension

Knotweed

Polygonum spp.

Polygonaceae

Description

There are 18 species and several varieties of knotweeds in Texas. These plants are herbs or herbaceous-textured vines without tendrils. They have alternate, usually lance-shaped leaves. The branching stems are erect or ascending; the enlarged nodes often take root where they contact bare ground. The very small, white to pinkish-red flowers usually form loose spikes.

Habitat

Knotweeds are found in all vegetational areas of Texas. They are usually found in wet areas and around ponds and streams, and are therefore more abundant in the eastern part of the state.

Toxic Agent

The toxic agent is not known. Consumption of these plants has been associated with primary photosensitization, and until research is completed to show otherwise, all species should be considered as potentially toxic. Vegetation from species associated with field cases contains photodynamic compounds not yet identified. Feeding trials with knotweed seed in grain screenings did not cause problems or disease.

Signs of Livestock Ingestion

The clinical signs are those of sunburn and include: Photophobia (animals try to stay in the shade); Reddening of light colored skin; Crusting and cracking of nonpigmented skin; Sloughing of affected skin.

Young calves on cows with severe udder lesions may not be allowed to nurse and can suffer significant weight loss.

Management Strategies

These plants are widespread, but are seldom consumed to any extent except in severe drought or overgrazed pastures. Feeding hay can prevent consumption and toxicity. Remove affected animals from the pasture and give them shade, feed and water.

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