Weed Identification and Control Flashcards
7 cards from real CCA practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Weed Identification and Control flashcards as text
Which herbicide mode of action group includes atrazine, simazine, and metribuzin?
Answer: Group 5 — Photosystem II inhibitors (serine binding)
Triazines and related compounds (Group 5) inhibit photosystem II at the QB binding site of the D1 protein, blocking electron transport and ultimately causing oxidative damage.
Field bindweed (Convolvulus arvensis) is particularly difficult to control because it:
Answer: Has an extensive deep root system with vegetative reproductive structures
Field bindweed has a deep, extensive root and rhizome system that can extend 20+ feet deep, enabling regrowth from fragments following tillage or herbicide application.
A pre-emergence herbicide is most accurately described as one applied:
Answer: Before weed seeds germinate, regardless of crop emergence timing
Pre-emergence herbicides are applied before target weed seedlings emerge from the soil, and they may be applied before or after crop planting.
Which of the following is the best example of biological weed control in US crop production?
Answer: Releasing Rhinocyllus conicus weevils to suppress musk thistle
Rhinocyllus conicus is a seed head weevil introduced as a classical biocontrol agent for musk thistle (Carduus nutans), a noxious invasive weed.
Which weed produces seeds with a pappus (feathery plume) that enables long-distance wind dispersal, making it a major challenge in perennial crops and roadsides?
Answer: Canada thistle (Cirsium arvense)
Canada thistle seeds have a feathery pappus that allows them to travel miles on the wind, making containment difficult and spread into new areas common.
Herbicide carryover in soil most commonly causes problems when:
Answer: A sensitive rotational crop is planted the following season
Herbicide carryover injures susceptible rotational crops planted in subsequent seasons when soil residues persist beyond expected half-lives due to low rainfall, low temperatures, or high pH.
What does the term 'soil half-life' (DT50) mean in the context of herbicide persistence?
Answer: The time required for 50% of the applied herbicide to degrade in the soil
DT50 (dissipation time 50%) is the time required for 50% of the initial herbicide concentration to break down in soil via microbial, chemical, or photodegradation processes.