Herbicide resistance is one of the largest problems in the field of weed science today. This problem is something that drives research and extension efforts in the program. This page includes confirmed and suspected cases of herbicide resistant weeds in Virginia.


The Big Three

In Virginia, there are three major herbicide resistant weeds that are a cause for concern for growers: Palmer amaranth, common ragweed, and horseweed/marestail. The maps below highlight in red where herbicide resistant weeds have been reported. It is likely that these weeds are resistant to glyphosate (WSSA group 9) and ALS-inhibiting (WSSA group 2) herbicides.

Italian Ryegrass

Italian ryegrass is another weed causing concern in Virginia. It is resistant to ALS-inhibiting herbicides and widespread across the eastern part of the state.

Common Waterhemp

Common waterhemp has been found in Virginia recently. Like the big three listed above, this weed is suspected to be resistant to glyphosate and ALS-inhibiting herbicides.



Common Lambsquarters

Resent research has shown evidence that common lambsquarters is resistant to glyphosate in the mid-Atlantic. Reduced control with glyphosate has been noted in field studies, as well. This research is ongoing and more results will be reported soon.

The list below is of confirmed cases of herbicide resistance found in Virginia. This list was taken from the International Survey of Herbicide Resistant Weeds and last updated on March 16, 2020.


Common Name

First Reported


Amaranthus hybridus

Smooth Pigweed


Photosystem II inhibitors (5)


ALS inhibitors (2)

Chenopodium album

Common Lambsquarters


Photosystem II inhibitors (5)

Lolium perenne ssp. multiflorum

Italian Ryegrass


ACCase inhibitors (1)

Amaranthus retroflexus

Redroot Pigweed


Photosystem II inhibitors (5)

Sorghum halepense



ACCase inhibitors (1)

Poa annua

Annual Bluegrass


Photosystem II inhibitors (5)

Sorghum bicolor



ALS inhibitors (2)

Conyza canadensis



EPSP synthase inhibitors (9)

Stellaria media

Common Chickweed


ALS inhibitors (2)

Amaranthus palmeri

Palmer Amaranth


EPSP synthase inhibitor (9)

Eleusine indica



PPO inhibitors (14)

What do growers in Virginia think of herbicide resistance?

 Surveys were conducted in 2015 to learn more about the spread of herbicide resistance and what growers are doing to mitigate resistance. From 97 responses, representing approximately 10% of Virginia’s corn, soybean, and small grains acreage, we see that many growers in the Commonwealth are combating herbicide resistance through changing herbicide practices such as rotating and introducing new modes of action and reintroducing tillage.