Weed Resistance Quiz Answers
Here are the answers to the weed resistance quiz. How many did you get correct?
1. Experts at the University of Illinois recently confirmed the first glyphosate-resistant weed in the state. What weed species did they identify?
A. Waterhemp
B. Horseweed
C. Common ragweed
Researchers recently confirmed a population of glyphosate-resistant waterhemp in Effingham, Ill. This particular waterhemp population is also ALS inhibitor-resistant, and it is believed that PPO inhibitor resistance is just around the corner.
2. One U.S. state holds the sole title of being the only state with four weeds confirmed resistant to glyphosate. What state is it?
A. Arkansas
B. Missouri
C. Kansas
Kansas has confirmed glyphosate resistance to horseweed, waterhemp, giant ragweed and common ragweed.
3. Stacked resistance, or resistance to multiple herbicide chemistries, can wreak havoc for growers and limit control options even further. There are a few cases of weeds with stacked resistance that include glyphosate herbicides. Name one.
A. Glyphosate- and ALS-resistant marestail (horseweed) in Ohio
B. Glyphosate- and ALS-resistant waterhemp in Illinois
C. Glyphosate-, ALS- and PPO-resistant waterhemp in Missouri
D. Options A and B
E. All of the above
4. Around the world, the number of unique cases of herbicide resistant weeds has dramatically increased over the last 20 years. What are the three most common modes of action for weeds to develop resistance to?
A. ALS inhibitors, ACCase inhibitors, glycines
B. ALS inhibitors, Photosystem II inhibitors, ACCase inhibitors
C. ACCase inhibitors, glycines, Photosystem II inhibitors
In order, the three most common modes of action for weeds to develop resistance to are ALS inhibitors, Photosystem II inhibitors and ACCase inhibitors.
5. What is the proper definition of herbicide resistance?
A. The incremental increase in tolerance of a weed population to a herbicide with
each generation, eventually leading to resistance
B. The inherited ability of a plant to survive and reproduce following exposure to
a dose of herbicide normally lethal to the wild type
C. The failure of a herbicide to kill a plant
According to the Weed Science Society of America, the definition of herbicide resistance is “the inherited ability of a plant to survive and reproduce following exposure to a dose of herbicide normally lethal to the wild type.”
6. How many unique herbicide-resistant weed biotypes are there in the United States today?
A. 70+
B. 15+
C. 50+
There are more than 50 unique herbicide-resistant weed biotypes confirmed in the United States.
7. There are very few new herbicides being developed by chemical companies. To bring a new herbicide to market generally takes 10 years and $200 million. What were the last new modes of action developed for cereals, soybeans and corn (respectively)?
A. ALS inhibitors, Glufosinate, Glufosinate
B. ACCase inhibitors, Glufosinate, HPPD inhibitors
C. ALS inhibitors, Glufosinate, HPPD inhibitors
*For cereals: ALS inhibitors, such as chlorsulfuron (Glean®), in 1982
*For soybeans: Glufosinate, or Liberty®, in 1994
*For corn: HPPD inhibitors, such as isoxaflutole (Balance®) in 1998 or mesotrione (Callisto®) in 2001
8. What country has the worst problem with grass weed resistance in the world?
A. Australia
B. United States
C. Brazil
Australia has the worst problem with grass weed resistance in the world. Populations of ryegrass have been confirmed resistant to as many as seven modes of action, including ACCase inhibitors, ALS inhibitors and Dinitroanilines. Glyphosate-resistant ryegrass species also pose a problem for Australian growers. Growers have taken to bailing and burning combine chaff to try to reduce survival of resistant weed seeds.
9. How long has glyphosate been on the market? When was it first used intensively over-the-top of crops?
A. 30+, 1996
B. 5+, 2000
C. 10+, 1991
While glyphosate has been available for over 30 years, it has only been used intensively over-the-top since 1996 when the introduction of glyphosate-tolerant crops entered the market. Just four years later in 2000, glyphosate resistance was first confirmed in row crops in horseweed (marestail) in the Delmarva Peninsula.
10. Since the first case of glyphosate resistance was confirmed in 2000, how many states across the country have confirmed glyphosate resistance?
A. 17
B. 19
C. 12
Since that time, glyphosate resistance has spread to 19 states in the U.S. and numerous countries around the world.
Glyphosate Resistance Timeline
1998: Rigid ryegrass-California
2000: Horseweed-Delaware
2001: Horseweed-Kentucky, Tennessee
2002: Horseweed-Indiana, Maryland, Missouri, New Jersey, Ohio
2003: Horseweed-Arkansas, Mississippi, North Carolina, Pennsylvania
2004: Common ragweed-Arkansas, Missouri
Italian ryegrass-Oregon
Giant ragweed-Ohio
2005: Horseweed-California
Palmer pigweed-Georgia
Common waterhemp-Missouri
Giant ragweed-Indiana
2006: Horseweed-Kansas, Nebraska
Palmer pigweed-Arkansas
Waterhemp-Kansas
Giant ragweed-Kansas
2007: Horeseweed-Michigan
Waterhemp-Illinois
Common ragweed-Kansas
Hairy fleabane-California
11. What can this picture tell us about possible resistance?
A. That there is possible resistance because the weed is not completely destroyed
B. That there is no possibility of resistance because the weed is dying
C. That there is possible resistance because there are dead weeds next to live ones
This picture indicates the possibility of weed resistance. The observation of dead weeds next to live weeds is a red flag to look for when scouting the fields. The following are additional recommendations:
*Look for stubborn weeds, unexpected flourishes and species that were not a serious problem before
*If resistance is indeed developing in a field, applying more glyphosate only accelerates the problem
*You can’t tell if a weed is glyphosate-resistant just by looking at it
*Testing results, either way, can help keep control costs (and frustration) in check
12. Once a grower identifies resistant weeds in his field, what percent of the population typically has already developed resistance?
A. 30%
B. 2%
C. 65%
According to Bryan Young, weed scientist at Southern Illinois University, many growers who identify herbicide-resistant weeds don’t identify the weed to be resistant until 30 percent of the population has developed resistance. In recent times, the Midwest has experienced increased problems with glyphosate-resistant giant ragweed and waterhemp, so it is especially important to identify any resistant weeds as soon as possible in order to begin managing the problem weeds.
13. Have you experienced weed resistance first-hand? What did you do to combat it?
If you are one of the many growers who have visited the Resistance Fighter Web site, you have already taken a step towards proactive weed resistance management, so give yourself an A on this quiz!