|Palmer amaranth, better known as pigweed|
Mizzou weed expert Kevin Bradley says that the spread of the plant is usually blamed on contaminated livestock feed, bedding, or seeds clinging to machinery. His findings about the birdseed vector were presented at the university's recent Integrated Pest Management field day.
It's research worth noting, since some kinds of Palmer amaranth can resist several kinds of herbicides. The tiny seeds were present in almost all of the birdseed the researchers screened, but seed mixes that contain millet tended to have the most. One sample "contained nearly 8,000 pigweed seeds in a single pound bag. That's a lot of pigweed since birdseed often sells in 50 lb. bags," Smith reports. Seeds for other weeds were also common in the birdseed samples, including ragweed, velvetleaf, and morning glory.