CCA Weed Identification and Control 3

Question 1

Which mechanism of herbicide resistance involves weeds metabolizing the herbicide more rapidly than susceptible biotypes?

Accepted Answer

Metabolic resistance

Answer

Metabolic resistance occurs when resistant plants possess enhanced enzyme systems (e.g., cytochrome P450s) that break down the herbicide before it can cause damage.

Question 2

Common cocklebur (Xanthium strumarium) is best identified by which characteristic?

Accepted Answer

Spiny burr fruits and rough triangular leaves

Answer

Common cocklebur produces distinctive spiny burs (involucres with two seeds) and has large, rough, triangular to heart-shaped alternate leaves.

Question 3

A grower applies an ALS-inhibiting herbicide and achieves poor control. Testing reveals the target enzyme has a single amino acid substitution. This is an example of:

Accepted Answer

Target-site resistance

Answer

Target-site resistance occurs when a mutation in the herbicide's target enzyme reduces binding affinity, preventing effective inhibition at labeled rates.

Question 4

Which of the following best describes the 'critical weed-free period'?

Accepted Answer

The period during crop growth when weeds must be absent to prevent significant yield loss

Answer

The critical weed-free period is the portion of the growing season during which the crop must be kept free of weeds to prevent economically significant yield reductions.

Question 5

Horseweed (marestail, Conyza canadensis) has become a major management challenge primarily because it:

Accepted Answer

Has developed resistance to both glyphosate and ALS-inhibiting herbicides

Answer

Horseweed biotypes resistant to both glyphosate and ALS inhibitors are widespread, necessitating use of alternative modes of action such as PPO inhibitors or synthetic auxins.

(CCA) Certified Crop Advisor Practice Test

(CCA) Certified Crop Advisor Practice Test

CCA Weed Identification and Control 3