MU studies pollinator mixes as one source of Palmer amaranth seeds

University of Missouri researchers, under the direction of MU Extension weed scientist Kevin Bradley, are finding that many popular pollinator mixes contain pigweed seed.

More than 60 percent of mixes screened by graduate student Eric Oseland had seeds of Palmer amaranth, the No. 1 weed to watch in the United States. Oseland and other researchers buy pollinator mixes from numerous sources and investigate the mixes for the presence of weed seeds. They plant the seeds and then identify weed seed viability. So far, they have identified viable Palmer amaranth seed as well as a number of other pigweed species.

The mixes come with good intentions to improve pollinator numbers, which have dwindled since the 1990s. The Conservation Reserve Program (CRP) Pollinator Habitat Initiative offers financial incentives to farmers who plant the mixes. One-third of the world’s food products need pollinators to grow, says the Farm Service Agency.

CRP promotes the increase of fast-blooming forage legumes and other inexpensive wildflowers. Missouri farmers must buy mixes from neighboring states to meet CRP regulations. “This is not necessarily a good thing,” Oseland says, “because Kansas and Arkansas are heavily infested with Palmer amaranth.”

Agronomists and weed scientists in Iowa and other Midwestern states also are studying the spread of Palmer amaranth through CRP pollinator mixes.

Oseland says farmers enrolled in CRP programs need to be alert to the presence of Palmer amaranth.

After planting CRP or pollinator mixes, scout fields for Palmer amaranth and pull the weeds while they are small. Remove plants from the field. Early detection is critical to control. Palmer amaranth plants can grow up to 3 inches per day, so act quickly, Oseland says. Right now, one of the only options for control of Palmer amaranth in these environments is removing them by hand. “Once it’s in a CRP or pollinator planting field, it’s hard to control. Once it puts on a seed head, your problem just grew exponentially,” he says.

Rapid infestation occurs when Palmer amaranth seeds drop to the ground. One plant can produce up to 1 million seeds. Palmer amaranth seeds are about the size of a pinhead, not unlike some other native seeds found in these mixes.

Oseland says pollinator mixes add to the growing number of ways that Palmer amaranth spreads. It enters fields through farm equipment, waterfowl, animal feed and animal bedding. Seeds can live in the soil for up to five years and remain viable.

“In short, any seed, feed or equipment coming onto your farm should be thoroughly examined for the presence or even the possibility of Palmer amaranth seed,” Bradley says.

Growers often confuse Palmer amaranth with waterhemp. About five pigweed species are common in Missouri. Palmer amaranth bears long petioles on leaves and large, sharp bracts at the leaf axils. The leaves are also arranged like a poinsettia’s. It is much easier to tell the difference between mature Palmer amaranth and waterhemp; Palmer amaranth’s spiny bracts and longer seed heads make it stand out. It also grows to 7 feet.

Oseland recommends MU Extension’s ID Weeds app to identify the weed (weedID.missouri.edu). Samples also may be sent to MU’s Plant Diagnostic Clinic (plantclinic.missouri.edu).

Source: Kevin Bradley, 573-882-4039