Palmer amaranth continues reign as most troublesome weed, WSSA finds

Palmer amaranthIt should come as no surprise that Palmer amaranth ranks as the most troublesome and difficult-to-control weed in 12 categories of broadleaf crops, fruits and vegetables, according to a survey conducted by the Weed Science Society of America. The most common weed was common lambsquarter, according to the survey.

Nearly 200 U.S. and Canadian weed scientists participated in the 2016 survey, the second conducted by WSSA. A 2015 baseline survey looked at the most common and troublesome weeds in 26 different crops and non-crop areas.

Six weed species appeared on both the “most troublesome” and “most common” lists, according to the 2016 survey. They include Palmer amaranth, common lambsquarters, horseweed, morningglory, waterhemp and common ragweed.

“Weed scientists have confirmed multiple cases of herbicide resistance in all six of these weed species, except for the morningglories where there is suspected resistance to glyphosate,” Dr. Lee Van Wychen, WSSA science policy director, said in a news release. “While each of these species has evolved traits that make them widespread and tough competitors in broadleaf crops like soybeans and cotton, there is no question that their difficulty to control with herbicides has pushed them to the top of the list in this survey.”

Although listed as the most troublesome weed in cotton only, Palmer amaranth was ranked first in the overall survey based on the number of respondents who cited it as a problem. Common lambsquarters is widely distributed across the northern half of the United States and southern Canada, earning it the most common weed in the survey.

TOP 10 WEEDS IN BROADLEAF CROPS, FRUITS & VEGETABLES 

Most Troublesome Most Common
1 Palmer amaranth 1 common lambsquarters
2 common lambsquarters 2 foxtail (giant, green, yellow)
3 horseweed (marestail) 3 morningglory (ivyleaf, pitted, tall)
4 morningglory (ivyleaf, pitted, tall) 4 Palmer amaranth
5 waterhemp (tall, common) 5 redroot pigweed
6 nutsedge (yellow, purple) 6 waterhemp (tall, common)
7 kochia 7 horseweed (marestail)
8 common ragweed 8 common ragweed
9 giant ragweed 9 barnyardgrass
10 nightshade (eastern black, hairy) 10 velvetleaf

Broken down by crop, here are the most troublesome and most common weeds.

BROADLEAF CROP MOST TROUBLESOME WEED MOST COMMON WEED
alfalfa Canada thistle dandelion
canola kochia wild oat
cotton Palmer amaranth morningglory (ivyleaf, pitted, tall)
fruits & nuts field bindweed horseweed (marestail)
peanuts nutsedge (yellow, purple) Palmer amaranth
pulse crops common lambsquarters common lambsquarters
soybeans horseweed, waterhemp (tall, common) waterhemp (tall, common)
sugar beets common lambsquarters common lambsquarters
vegetables nutsedge (yellow, purple) common lambsquarters

WSSA plans to conduct habitat-specific weed surveys annually. The 2017 survey will focus on weeds in grass crops, pasture and turf, while the 2018 survey will focus on weeds in aquatic environments, natural areas and other noncrop settings.

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