GTBOP Moodle Quiz¶
Weed Control in the Landscape & Nursery — Dr. Mark Czarnota (November 18, 2021)¶
Source: Corrected SRT (Stage 1) — GTBOP_Transcript_2021-11-18_WeedControl.srt (786 blocks) Structural Reference: Stage 2 Archive Package — GTBOP_Archive_Summary_2021-11-18_WeedControl.md Questions: 15 Difficulty Distribution: 6 Recall (40%) / 6 Application (40%) / 3 Analysis (20%)
Question 1¶
Timestamp Reference: 4:28 – 5:06 Difficulty: Recall
Which of the following did Dr. Czarnota identify as one of the six characteristics that predict whether a plant is likely to become a weed?
a) Tolerance to herbicide applications b) Presence of a vegetative reproductive structure c) Ability to grow in full shade d) Resistance to insect feeding
Correct Answer: b Explanation: Czarnota listed six predictive characteristics of weediness, the first being the presence of a vegetative reproductive structure, using yellow and purple nutsedge as examples. Source in transcript: ~4:28–5:06, blocks 98–114
Question 2¶
Timestamp Reference: 5:13 – 6:16 Difficulty: Recall
What weed did Dr. Czarnota describe as a problem in propagation houses growing azaleas, for which a promising fungicide-based control product ultimately failed to receive EPA registration?
a) Chamberbitter b) Purple nutsedge c) Marchantia d) Dogfennel
Correct Answer: c Explanation: Czarnota described Marchantia as a liverwort problem in greenhouse propagation of azaleas. A fungicide already labeled in Europe showed promise as a control but was rejected by EPA due to how the toxicology was written up. Source in transcript: ~5:13–6:40, blocks 118–137
Question 3¶
Timestamp Reference: 14:48 – 15:36 Difficulty: Application
A landscape manager notices bare soil exposed between newly planted shrubs after mulch has decomposed. Based on Dr. Czarnota's recommendations, what is the most appropriate first response?
a) Apply a post-emergent herbicide to the bare soil b) Restore the mulch layer to two to four inches c) Install landscape fabric over the bare soil d) Apply a pre-emergent herbicide at double the label rate
Correct Answer: b Explanation: Czarnota repeatedly emphasized that bare soil will always produce weed growth, and recommended maintaining a two-to-four-inch layer of composted organic mulch, refreshed once or twice per year. Source in transcript: ~15:01–15:36, blocks 251–256
Question 4¶
Timestamp Reference: 15:44 – 16:07 Difficulty: Recall
According to Dr. Czarnota, how many grass carp per surface acre are recommended for controlling submerged aquatic weeds in a small pond?
a) 2–4 b) 8–10 c) 15–20 d) 25–30
Correct Answer: b Explanation: Czarnota recommended stocking about 8 to 10 grass carp per surface acre for effective control of submerged aquatic weeds in small ponds. Source in transcript: ~16:00–16:07, blocks 260–261
Question 5¶
Timestamp Reference: 17:00 – 18:06 Difficulty: Application
A pasture manager has a large infestation of musk thistle and wants to reduce its spread over two to three years without relying heavily on herbicides. Based on Dr. Czarnota's presentation, which biological control approach would be most appropriate?
a) Release grass carp into nearby water features b) Introduce geese to graze the thistle c) Release thistle weevil eggs around the thistle plants d) Apply the bioherbicide DeVine to the thistle
Correct Answer: c Explanation: Czarnota described the thistle weevil as a successful biocontrol agent for musk thistle. The weevil larvae feed on developing seed heads, preventing reproduction and reducing populations over a two-to-three-year period. DeVine was developed for strangler vine in citrus, not thistle. Source in transcript: ~17:29–18:06, blocks 287–298
Question 6¶
Timestamp Reference: 21:07 – 22:00 Difficulty: Application
A landscaper applies a pre-emergent herbicide in late February in Georgia but receives no rain for the following two weeks. What is the most likely outcome?
a) The herbicide will still provide full-season weed control b) The herbicide will not be activated and weed control will be significantly reduced c) The herbicide will become toxic to nearby ornamentals d) The herbicide will leach below the root zone
Correct Answer: b Explanation: Czarnota explained that pre-emergent herbicides need a rain event of about a half inch to one inch to move the product into the top quarter inch of soil where seeds germinate. He later noted that if no rain occurs within 72 hours, weed control starts to diminish. Source in transcript: ~21:19–21:55 and ~38:55–39:07, blocks 352–356 and 607–609
Question 7¶
Timestamp Reference: 22:18 – 22:40 Difficulty: Recall
What happens to glyphosate when it contacts bare soil, according to Dr. Czarnota?
a) It remains active in the soil for up to 12 weeks b) It is absorbed by the soil particles and inactivated immediately c) It leaches into groundwater within 24 hours d) It continues to provide pre-emergent weed control
Correct Answer: b Explanation: Czarnota stated that when glyphosate is sprayed on the ground, it is inactivated immediately because it bonds to soil particles and eventually breaks down into carbon, hydrogen, and oxygen. Source in transcript: ~22:20–22:45, blocks 372–374
Question 8¶
Timestamp Reference: 26:36 – 27:04 Difficulty: Analysis
Dr. Czarnota explained that glyphosate inhibits the EPSP synthase pathway, which produces three amino acids: tryptophan, phenylalanine, and tyrosine. Why does this mode of action contribute to glyphosate's low mammalian toxicity?
a) These amino acids are not essential for human health b) Mammals have a backup pathway that produces these amino acids c) The EPSP synthase pathway does not exist in humans or any animals d) Glyphosate breaks down before it can reach mammalian cells
Correct Answer: c Explanation: Czarnota emphasized that no animals have the EPSP synthase pathway — humans must obtain tryptophan, phenylalanine, and tyrosine through their diet. Because glyphosate targets a pathway absent from animal biology, it is one of the reasons for its low toxicity to mammals. Source in transcript: ~26:36–27:04, blocks 444–451
Question 9¶
Timestamp Reference: 28:22 – 29:08 Difficulty: Recall
According to Dr. Czarnota, what is the mode of action of dinitroaniline herbicides such as Treflan, pendimethalin, and Barricade?
a) Inhibition of photosynthesis b) Disruption of cell membrane integrity c) Disruption of microtubule formation during cell division d) Inhibition of amino acid production
Correct Answer: c Explanation: Czarnota explained that dinitroaniline herbicides bind to microtubules, the structures that pull chromosomes apart during cell division. This prevents cells from dividing properly and laying down a new cell plate, resulting in club-rooted growth symptoms. Source in transcript: ~28:22–29:08, blocks 468–476
Question 10¶
Timestamp Reference: 29:42 – 30:50 Difficulty: Application
A landscape professional needs a pre-emergent herbicide that is safe for use on most turfgrasses, broad woody ornamentals, and some perennials and annuals. Which product did Dr. Czarnota describe as significantly underutilized for this purpose?
a) Marengo (indaziflam) b) Snapshot (isoxaben + trifluralin) c) Dimension (dithiopyr) d) BroadStar (flumioxazin)
Correct Answer: c Explanation: Czarnota specifically called Dimension (dithiopyr) one of the most underutilized pre-emergent herbicides and noted it can be safely sprayed in most turfgrasses and landscape situations including broad woody ornamentals and even some perennials and annuals. Source in transcript: ~29:54–30:28, blocks 491–497
Question 11¶
Timestamp Reference: 30:40 – 31:07 Difficulty: Recall
How many weeks of pre-emergent weed control did Dr. Czarnota say Marengo (indaziflam) can provide in established woody ornamentals?
a) 6–8 weeks b) 8–10 weeks c) 10–12 weeks d) Up to 16 weeks
Correct Answer: d Explanation: Czarnota described Marengo (indaziflam) as one of the best products he had tested, providing upwards of 16 weeks of pre-emergent weed control, though mainly for established woody ornamentals. He noted it would not control nutsedge. Source in transcript: ~30:43–31:04, blocks 501–504
Question 12¶
Timestamp Reference: 36:15 – 36:39 Difficulty: Analysis
Dr. Czarnota compared the cost of hand weeding an acre of one-gallon container ornamentals ($1,200–$1,600) to the cost of chemical weed control (less than $200). Based on the application frequency he recommended for container production, what is the approximate annual cost range for chemical weed control per acre?
a) Less than $200 total b) $400–$600 c) $800–$1,200 d) $1,200–$1,600
Correct Answer: c Explanation: Czarnota stated chemical weed control costs less than $200 per application and recommended four to six applications per year for container production. At $200 per application times four to six applications, the annual cost would be approximately $800–$1,200 per acre. Source in transcript: ~36:19–36:39 and 38:40–38:45, blocks 572–575 and 602–604
Question 13¶
Timestamp Reference: 37:52 – 38:06 Difficulty: Application
A nursery grower is using a granular pre-emergent herbicide on container ornamentals. Why might the granular formulation be preferable to a sprayable formulation in this situation, according to Dr. Czarnota?
a) Granulars are always cheaper than sprayable formulations b) Granulars fall through the plant canopy to the ground, reducing contact with foliage c) Granulars provide longer residual control than sprays d) Granulars do not require activation by rainfall
Correct Answer: b Explanation: Czarnota explained that granular formulations fall through the plant canopy to hit the ground, then release herbicide when rain occurs. Sprays contact the plant foliage directly, increasing the risk of damage. However, he noted granulars are more expensive per unit of active ingredient and provide somewhat poorer weed control than sprays. Source in transcript: ~37:52–38:06, blocks 595–598
Question 14¶
Timestamp Reference: 45:12 – 45:55 Difficulty: Application
A grower asks about controlling torpedograss in an ornamental planting. Based on Dr. Czarnota's response, which product did he recommend, and what important limitation did he note?
a) Glyphosate — it is non-selective and will damage ornamentals b) Sandea (halosulfuron) — it only controls nutsedge species, not grasses c) Drive (quinclorac) — it is not yet labeled for over-top use on ornamentals d) Clethodim (Envoy) — it only suppresses bermudagrass, not torpedograss
Correct Answer: c Explanation: Czarnota recommended Drive (quinclorac) as very effective on torpedograss and noted his university research showed it to be fairly safe on most woody ornamentals. However, he cautioned that it is not yet labeled for over-top ornamental use, so it would not be a labeled application. Source in transcript: ~45:12–45:55, blocks 710–720
Question 15¶
Timestamp Reference: 27:18 – 27:43 Difficulty: Analysis
Dr. Czarnota described the NIH shift as one mechanism by which grasses detoxify 2,4-D. What does this tell us about why 2,4-D can be used as a selective herbicide in grass crops?
a) Grasses absorb 2,4-D more slowly than broadleaf plants b) Grasses have enzyme systems that chemically modify the 2,4-D molecule, inactivating it c) 2,4-D only penetrates broadleaf plant cuticles, not grass cuticles d) Grasses store 2,4-D in their roots where it cannot cause harm
Correct Answer: b Explanation: Czarnota explained that grasses have an enzyme system (the NIH shift) that can change the position of chlorine groups on the 2,4-D molecule, effectively inactivating it. This biochemical detoxification mechanism is one of the ways grasses tolerate 2,4-D, making it useful as a selective broadleaf herbicide in grass crops. Source in transcript: ~27:18–27:43, blocks 453–459
Generated for UGA Center for Urban Agriculture / GTBOP Moodle Course Activities Source: Corrected SRT (Stage 1) — GTBOP_Transcript_2021-11-18_WeedControl.srt (786 blocks) Structural Reference: Stage 2 Archive Package