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Best of NAMA 2020

By Margy Eckelkamp, The Scoop

What weeds are causing the most angst for weed scientists? A 2020 survey from the Weed Science Society of America (WSSA) had 315 responses from U.S. and Canadian weed scientists citing what weeds were the most prevalent and most troublesome.

By crop, here are the weeds the scientists put in the bull's-eye for seven grass crops: corn; rice; sorghum; turf; spring cereal grains; winter cereal grains; and pastureland, rangeland and other hay.

Most Troublesome, Hard to Control Weeds
Corn: Palmer amaranth and waterhemp
Pasture, rangeland and other hay: Canada thistle
Rice: Sedge spp. (yellow nutsedge and rice flatsedge) and Echinochloa (barnyardgrass and coast cockspur)
Spring cereal grains: Foxtail spp. (green and yellow foxtail)
Sorghum: Palmer amaranth and johnsongrass
Turf: Bluegrass spp. (annual and roughstalk bluegrass)
Winter cereal grains: Italian ryegrass and Bromus (downy and Japanese brome, cheat, rescuegrass)

Most Commonly Found Weeds
Corn: Common lambsquarters and foxtail spp. (green, yellow and giant foxtail)
Pasture, rangeland and other hay: Bromus (downy, red and smooth brome, cheat) and Canada thistle
Rice: Sedge spp. (yellow nutsedge and rice flatsedge) and barnyardgrass
Spring cereal grains: Common lambsquarters and foxtail spp. (green, yellow and giant foxtail)
Sorghum: Palmer amaranth
Turf: Crabgrass spp. (large, smooth and southern crabgrass)
Winter cereal grains: Lamium (henbit and purple deadnettle)

From the survey, the weed with the most notoriety is the Palmer amaranth, which was:
Ranked as the most troublesome weed in corn
Ranked as both the most troublesome and the most common weed in sorghum

"Palmer amaranth grows rapidly, has an extensive root structure and produces massive amounts of seeds that are easily transported and spread," Stanley Culpepper, professor and extension weed scientist at the University of Georgia said in the WSSA survey report. "Even more impressive are its genetic capabilities. Palmer amaranth can quickly evolve resistance to many important herbicides and has the potential to transfer that resistance to new plants through pollen movement."

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