International Survey of Herbicide-Resistant Weeds

Countries Weeds Herbicides Mutations Graphs References Researchers
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Status of Herbicide Resistance in Pennsylvania - William Curran : January, 2014

Horseweed is the most widespread problematic GR species in our state. It was mostly confined to the Southeastern region, but can now be found throughout the SE, Central, and parts of Western PA. Farmers are still managing it with herbicides (2,4-D, PPO, ALS, etc.) and not tillage. GR Palmer amaranth was first identified in Sept. 2013. It was discovered in double-crop soybeans or in noncrop environments. There are currently 7 to 9 farms that we know of that have the problem. They are mostly in Southeastern PA. Imported feed or hay likely introduced this weed to our region. We are exploring adding it to our noxious weed list and trying to alert the farming community about this potential problem. We have not yet done a greenhouse assay on the resistance, but almost all of the situations we encountered came from soybeans treated multiple times. We will try to do some tests this winter.

Herbicide Resistant Weeds in Pennsylvania, United States.
#YearSpeciesSite of ActionActivesContacts
1 263Common Lambsquarters1980Chenopodium album
Common Lambsquarters
United States
(Pennsylvania)
PennsylvaniaPA Photosystem II inhibitors (C1/5) Photosystem II inhibitors (C1/5) atrazine William Curran
2 264Smooth Pigweed1980Amaranthus hybridus (syn: quitensis)
Smooth Pigweed
United States
(Pennsylvania)
PennsylvaniaPA Photosystem II inhibitors (C1/5) Photosystem II inhibitors (C1/5) atrazine William Curran
3 5021Redroot Pigweed1998Amaranthus retroflexus
Redroot Pigweed
United States
(Pennsylvania)
Pennsylvania  ALS inhibitors (B/2), Photosystem II inhibitors (C1/5) Multiple Resistance: 2 Sites of Action
ALS inhibitors (B/2)
Photosystem II inhibitors (C1/5)
atrazine, chlorimuron-ethyl, cloransulam-methyl, imazamox, imazaquin, imazethapyr, primisulfuron-methyl, thifensulfuron-methyl William Curran, Dwight Lingenfelter
4 5121Shattercane2001Sorghum bicolor
Shattercane
United States
(Pennsylvania)
Pennsylvania  ALS inhibitors (B/2) ALS inhibitors (B/2) imazamox, imazethapyr, nicosulfuron, oxasulfuron, primisulfuron-methyl William Curran
5 5258Horseweed2003Conyza canadensis
Horseweed
United States
(Pennsylvania)
Pennsylvania  EPSP synthase inhibitors (G/9) EPSP synthase inhibitors (G/9) glyphosate William Curran
6 5259Giant Foxtail2004Setaria faberi
Giant Foxtail
United States
(Pennsylvania)
Pennsylvania  ALS inhibitors (B/2) ALS inhibitors (B/2) foramsulfuron, imazamox, nicosulfuron William Curran
7 7778Common Ragweed2008Ambrosia artemisiifolia
Common Ragweed
United States
(Pennsylvania)
Pennsylvania  EPSP synthase inhibitors (G/9) EPSP synthase inhibitors (G/9) glyphosate William Curran, Dwight Lingenfelter
8 7898Common Chickweed2010Stellaria media
Common Chickweed
United States
(Pennsylvania)
Pennsylvania  ALS inhibitors (B/2) ALS inhibitors (B/2) pyroxsulam, thifensulfuron-methyl, tribenuron-methyl William Curran
9 7779Palmer Amaranth2013Amaranthus palmeri
Palmer Amaranth
United States
(Pennsylvania)
Pennsylvania  EPSP synthase inhibitors (G/9) EPSP synthase inhibitors (G/9) glyphosate William Curran, Dwight Lingenfelter
Contributing Weed Scientists
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Cite this site as: Heap, I.  The International Survey of Herbicide Resistant Weeds.  Online.  Internet.  Wednesday, August 21, 2019 .  Available  www.weedscience.org
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