Weed Identification and Control Flashcards
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Read the first 7 Weed Identification and Control flashcards as text
Which mechanism of herbicide resistance involves weeds metabolizing the herbicide more rapidly than susceptible biotypes?
Answer: Metabolic resistance
Metabolic resistance occurs when resistant plants possess enhanced enzyme systems (e.g., cytochrome P450s) that break down the herbicide before it can cause damage.
Common cocklebur (Xanthium strumarium) is best identified by which characteristic?
Answer: Spiny burr fruits and rough triangular leaves
Common cocklebur produces distinctive spiny burs (involucres with two seeds) and has large, rough, triangular to heart-shaped alternate leaves.
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:
Answer: Target-site resistance
Target-site resistance occurs when a mutation in the herbicide's target enzyme reduces binding affinity, preventing effective inhibition at labeled rates.
Which of the following best describes the 'critical weed-free period'?
Answer: The period during crop growth when weeds must be absent to prevent significant yield loss
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.
Horseweed (marestail, Conyza canadensis) has become a major management challenge primarily because it:
Answer: Has developed resistance to both glyphosate and ALS-inhibiting herbicides
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.
Which cultural practice has been shown to reduce weed pressure by depleting the weed seedbank over time?
Answer: Stale seedbed technique
The stale seedbed technique stimulates weed seed germination before crop planting, then destroys emerged seedlings with shallow tillage or contact herbicides, depleting the seedbank.
Palmer amaranth (Amaranthus palmeri) is distinguished from other pigweeds primarily by:
Answer: Extremely rapid growth rate and petioles longer than the leaf blade
Palmer amaranth can grow over 2 inches per day under ideal conditions and has characteristically long petioles that often exceed the length of the leaf blade.