Research has demonstrated that Palmer amaranth has a higher growth rate and is more competitive than other pigweed species.
"Growth rates approaching 3 inches per day and yield losses of 78% (soybean) and 91% (corn) attributed to Palmer amaranth interference have been reported in the scientific literature," Hager notes. "Seed production capability of female Palmer amaranth plants is similar to that of female waterhemp plants."
Hager described the cotyledon leaves of Palmer amaranth as being relatively long compared with other Amaranthus species.
"Like all weedy Amaranthus species in Illinois, the true leaves—those produced after the cotyledon leaves—of Palmer amaranth have a small notch in the tip," he adds.
Occasionally, a single hair can be found in the leaf notch. This hair may not be present in each leaf notch of a Palmer amaranth plant, and tends to be less common on leaves of waterhemp plants. The stems and leaves have no or few hairs and the stems feel smooth to the touch.
"Leaves alternate on the stem and are generally lance-shaped or egg-shaped with prominent white veins on the underside," he adds. "As plants become older, they often assume a poinsettia-like appearance and sometimes have a white or purple chevron on the leaves. Leaves are attached to the stem by petioles that are usually longer than the leaf blade."
Source: University of Illinois