International Survey of Herbicide-Resistant Weeds

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Status of Herbicide Resistance in Kentucky - James Martin : February, 2014

Glyphosate-resistant horseweed was first observed in no-till soybeans in a couple of fields in Kentucky in 2001 and is now widespread throughout the state. Isolated problems with Palmer amaranth and waterhemp in western Kentucky were reported between 2005 and 2010. It wasn’t until 2010 that these populations were confirmed to be resistant to glyphosate. Excessive flooding during the springs of 2010 and 2011 caused a rapid spread of both pigweed species. Recent methods for spreading these weeds are with equipment and with dairy operations importing Palmer-infested cotton seed from the South. Approximately half of the populations of Palmer amaranth and waterhemp are also resistant to ALS inhibitors. Problems with horseweed, Palmer amaranth, and waterhemp are not as prevalent in soybean or corn fields where winter wheat is included as a rotational crop compared with other rotations. However, recent developments indicate herbicide-resistant weeds such as ALS-resistant Italian ryegrass, and ALS- resistant common chickweed are present in wheat. Previously reported incidences of ACCase-resistant and ALS-resistant johnsongrass were only isolated problems in a few fields. Also, with current weed management practices triazine-resistant and ALS-resistant smooth pigweed is no longer a concern at this time in Kentucky.

Herbicide Resistant Weeds in Kentucky, United States.
#YearSpeciesSite of ActionActivesContacts
1 489Smooth Pigweed1987Amaranthus hybridus (syn: quitensis)
Smooth Pigweed
United States
(Kentucky)
Kentucky  Photosystem II inhibitors (C1/5) Photosystem II inhibitors (C1/5) atrazine, simazine Jonathan Green
2 488Johnsongrass1991Sorghum halepense
Johnsongrass
United States
(Kentucky)
KentuckyKY ACCase inhibitors (A/1) ACCase inhibitors (A/1) fluazifop-P-butyl William Witt, Jonathan Green
3 490Smooth Pigweed1992Amaranthus hybridus (syn: quitensis)
Smooth Pigweed
United States
(Kentucky)
KentuckyKY ALS inhibitors (B/2) ALS inhibitors (B/2) chlorimuron-ethyl, flumetsulam, imazaquin, imazethapyr, nicosulfuron, primisulfuron-methyl, thifensulfuron-methyl William Witt, Jonathan Green
4 5208Horseweed2001Conyza canadensis
Horseweed
United States
(Kentucky)
Kentucky  EPSP synthase inhibitors (G/9) EPSP synthase inhibitors (G/9) glyphosate C B Rogers, James Martin
5 7877Italian Ryegrass2004Lolium perenne ssp. multiflorum
Italian Ryegrass
United States
(Kentucky)
Kentucky  ACCase inhibitors (A/1) ACCase inhibitors (A/1) diclofop-methyl William Witt
6 7878Giant Ragweed2005Ambrosia trifida
Giant Ragweed
United States
(Kentucky)
Kentucky  EPSP synthase inhibitors (G/9) EPSP synthase inhibitors (G/9) glyphosate Jonathan Green
7 7879Common Ragweed2006Ambrosia artemisiifolia
Common Ragweed
United States
(Kentucky)
Kentucky  EPSP synthase inhibitors (G/9) EPSP synthase inhibitors (G/9) glyphosate James Martin
8 7880Johnsongrass2006Sorghum halepense
Johnsongrass
United States
(Kentucky)
Kentucky  ALS inhibitors (B/2) ALS inhibitors (B/2) foramsulfuron, nicosulfuron, primisulfuron-methyl Jonathan Green
9 7881Tall Waterhemp2010Amaranthus tuberculatus (=A. rudis)
Tall Waterhemp
United States
(Kentucky)
Kentucky  EPSP synthase inhibitors (G/9) EPSP synthase inhibitors (G/9) glyphosate James Martin
10 7882Palmer Amaranth2010Amaranthus palmeri
Palmer Amaranth
United States
(Kentucky)
Kentucky  EPSP synthase inhibitors (G/9) EPSP synthase inhibitors (G/9) glyphosate James Martin
11 7883Common Chickweed2013Stellaria media
Common Chickweed
United States
(Kentucky)
Kentucky  ALS inhibitors (B/2) ALS inhibitors (B/2) chlorsulfuron, flucarbazone-sodium, thifensulfuron-methyl, tribenuron-methyl James Martin
12 7891Italian Ryegrass2013Lolium perenne ssp. multiflorum
Italian Ryegrass
United States
(Kentucky)
Kentucky  ALS inhibitors (B/2) ALS inhibitors (B/2) mesosulfuron-methyl, pyroxsulam James Martin
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Cite this site as: Heap, I.  The International Survey of Herbicide Resistant Weeds.  Online.  Internet.  Friday, October 20, 2017 .  Available  www.weedscience.org
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