Herbicide Resistant Weeds

Thursday, September 09, 2010

What's on this page

Lambsquarters

1.	Resistant Weeds of Maryland
2.	Resistance in Neighboring States
3.	Fact Sheets & Literature
4.	Resistance Experts in Maryland
5.	Contributing Weed Scientists
6.	Acknowledgements
7.	Where to now?

If we do not have a picture for this weed, or you can provide a better picture (scan, digital camera etc) please please e-mail it to us.

Lambsquarters (Chenopodium album) is the most widespread resistant weed of Maryland

Introduction

About this page

There are currently 11 different types (known as 'biotypes') of herbicide resistant weeds in Maryland. The first herbicide resistant weed reported from Maryland is Smooth Pigweed (Amaranthus hybridus) with resistance to atrazine, reported in 1972. Local weed scientists estimate that there are 1,520 sites and more than 12,800 acres infested with herbicide resistant weeds in Maryland and they infest corn, cropland, soybean, Unspecified, and wheat. The most widespread resistant weed of Maryland is Lambsquarters (Chenopodium album), which infests an estimated 1001-10000 acres and is found primarily in corn, and cropland. Common Chickweed (Stellaria media), with resistance to chlorsulfuron, mesosulfuron-methyl, thifensulfuron-methyl, and tribenuron-methyl is the most recently discovered (2009) new type of resistant weed in Maryland.

This is a resource page to assist you in managing herbicide-resistant weeds in Maryland . If you have any questions regarding herbicide-resistant weeds in Maryland please contact an expert in your area. If you have encountered a computer related error on the site then contact support@weedscience.org. If you are a weed scientist wanting to add or correct information on this page then please contact research@weedscience.org or add the information directly.

Scroll down this page to view tables on herbicide resistant weeds in Maryland and its adjacent states as well as a list of articles about herbicide resistant weeds in your region. Click on the links within the table to view a case of resistance in more detail.

HERBICIDE RESISTANT WEEDS IN MARYLAND
Weed	Situation	Herbicide Mode of Action	Year
Smooth Pigweed (Amaranthus hybridus)	corn, cropland	C1/5 - Photosystem II inhibitors (atrazine)	1972
Barnyardgrass (Echinochloa crus-galli)	corn, cropland	C1/5 - Photosystem II inhibitors (atrazine, cyanazine, simazine)	1978
Lambsquarters (Chenopodium album)	corn, cropland	C1/5 - Photosystem II inhibitors (atrazine)	1982
Velvetleaf (Abutilon theophrasti)	corn, cropland	C1/5 - Photosystem II inhibitors (atrazine)	1984
Giant Foxtail (Setaria faberi)	corn, cropland	C1/5 - Photosystem II inhibitors (atrazine)	1984
Yellow Foxtail (glauca) (Setaria glauca)	corn, cropland	C1/5 - Photosystem II inhibitors (atrazine, cyanazine, simazine)	1984
Redroot Pigweed (Amaranthus retroflexus)	Unspecified	B/2 - ALS inhibitors (imazaquin, imazethapyr)	1998
Italian Ryegrass (Lolium multiflorum)	wheat	A/1 - ACCase inhibitors (diclofop-methyl)	1998
Common cocklebur (Xanthium strumarium)	Unspecified	B/2 - ALS inhibitors (chlorimuron-ethyl, imazaquin, imazethapyr)	1998
Horseweed (Conyza canadensis)	soybean	G/9 - Glycines (glyphosate)	2002
Common Chickweed (Stellaria media)	wheat	B/2 - ALS inhibitors (chlorsulfuron, mesosulfuron-methyl, thifensulfuron-methyl, tribenuron-methyl)	2009

HERBICIDE RESISTANT WEEDS IN ADJACENT STATES

DELAWARE
Species	MOA	Year
Smooth Pigweed	C1/5	1977
Lambsquarters	C1/5	1988
Smooth Pigweed	B/2	2000
Horseweed	G/9	2000
Horseweed	D/22	2003
Common Ragweed	B/2	2005
Common Ragweed	E/14	2005

PENNSYLVANIA
Species	MOA	Year
Smooth Pigweed	C1/5	1980
Lambsquarters	C1/5	1980
Redroot Pigweed	B/2	1998
Redroot Pigweed	C1/5	1998
Shattercane	B/2	2001
Horseweed	G/9	2003
Giant Foxtail	B/2	2004

VIRGINIA
Species	MOA	Year
Smooth Pigweed	C1/5	1976
Lambsquarters	C1/5	1979
Redroot Pigweed	C1/5	1993
Italian Ryegrass	A/1	1993
Smooth Pigweed	B/2	1994
Johnsongrass	A/1	1995
Annual Bluegrass	C1/5	2001
Shattercane	B/2	2003
Common Chickweed	B/2	2008

HERBICIDE RESISTANT WEED CONTACTS IN MARYLAND

Your local state university extension agent or local department of agriculture representative may be able to provide you with more information on herbicide-resistant weeds in your region. Much of the information about herbicide-resistant weeds in Maryland has been provided by the following experts.

STATE CONTACTS

RONALD RITTER

University of Maryland
12901 North Point Lane
Laurel, 20708, Maryland
United States of America
Phone : (301) 405-1329
Fax : (301) 314-9041
Email Ronald Ritter

Acknowledgements

Where to now?

The North American Herbicide Resistance Action Committee and weed scientists in Maryland have been instrumental in providing you this information. Particular thanks is given to Ronald Ritter for providing detailed information.

1.	Resistant Weeds Globally
2.	Resistant Weeds in the USA
3.	Herbicides
4.	Weed Researchers
5.	Comment on this site
6.	Search this site