Images: Distinguishing spines on the nodes of a spiny amaranth plant; University of Florida (left), and a spiny amaranth seedling; VA Tech (right).
Spiny amaranth is a pigweed present in many US states in the midwest, east, south, and California, with glyphosate-resistant populations confirmed in Mississippi. Spiny amaranth can become a problem weed in pastures that are over-grazed and are in need of increased management. It is a competitive weed, and has been associated with nitrate accumulation in livestock. It is identified from other pigweeds by pairs of spines at each node on the stem. While mowing can slow growth, the plants grow back and produce seed. So, integrating multiple control measures is necessary and depends on the severity of the infestation.
- A few individual plants or stands can be removed by hand, and should be removed to prevent a larger infestation from developing
- Larger infestations may be mowed repeatedly or burned
- Smaller plants can be controlled with effective herbicide modes of action, so herbicide application should be performed when plants are young
- Strong, vigorous pastures will largely out-compete spiny amaranth. So, correct soil pH, soil nutrient applications, and avoiding over-grazing are all important for suppressing this weed.
Herbicide resistant populations:
- Group 9
Locations of resistant populations: