Skip to content

# GTBOP Moodle Review Activities

## Weed Control in Turf — A Review of the Basics and Recent Updates

Webinar Date: November 17, 2017 Speaker: Dr. Patrick McCullough, Weed Scientist, University of Georgia Series: Green & Commercial Course Context: Weed Science Certificate Course Source: Corrected SRT (Stage 1) + Archive Package (Stage 2)

### Review Task 1: Weed Identification Characteristics

Watch: 2:43 – 9:33 Task: As McCullough walks through the diagnostic characteristics used to identify weed species, list the six types of characteristics he covers and note one specific example species he uses to illustrate each. Key Points to Identify: - Seed heads (e.g., bahiagrass vs. dallisgrass, Poa annua panicle) - Ligules (e.g., barnyardgrass absent ligule vs. crabgrass fleshy ligule) - Flowers (e.g., two-petal vs. three-petal day flower species) - Leaf arrangement on stems (alternate vs. opposite) - Pubescence/hairs (e.g., smooth crabgrass vs. large crabgrass vs. southern crabgrass) - Leaf markings (e.g., white clover chevron vs. spotted burr clover purple dot)

### Review Task 2: Cultural Practices and Weed Competition

Watch: 17:08 – 21:26 Task: McCullough presents two research studies demonstrating how cultural practices influence weed populations. Summarize the key finding of each study, including the specific numbers he provides. Key Points to Identify: - Mowing height study: tall fescue at 1 inch vs. 4 inches — crabgrass reduced from 95% to 0% - Irrigation study: daily watering vs. as-needed — dollarweed cover increased 5–6 fold with daily irrigation - The connection between these findings and reducing the need for herbicide inputs

### Review Task 3: Pre-Emergent Herbicide Mechanism

Watch: 24:07 – 27:00 Task: McCullough explains a common misconception about how pre-emergent herbicides work. Identify what pre-emergent herbicides do NOT do and then describe the actual mechanism in three steps (where the product goes, how the weed encounters it, what happens to the seedling). Key Points to Identify: - Pre-emergents do NOT prevent germination - Product binds in the upper half-inch of the soil profile - Germinating seedling roots and shoots absorb the herbicide from soil water solution - Herbicide inhibits cell division; seedling fails to establish healthy roots and dies

### Review Task 4: Herbicide Resistance Selection Pressure

Watch: 37:31 – 43:33 Task: McCullough uses a year-by-year diagram to explain how herbicide resistance develops through selection pressure. Trace the progression from Year 1 through Year 5 and explain why simply increasing the herbicide rate does not solve the problem. Key Points to Identify: - Year 1: one naturally resistant biotype survives among susceptible population - Repeated applications kill susceptible plants, allowing resistant biotype to reproduce - By Year 5: resistant biotype dominates the population - Target-site resistance: altered binding site means the herbicide simply does not work regardless of rate (300x rate example with Monument)

### Review Task 5: Resistance Management Through Mode of Action Combinations

Watch: 46:05 – 50:48 Task: McCullough describes the results of resistance management trials at three golf courses. For each course, note which herbicides worked, which failed, and explain why the combination of a sulfonylurea with simazine succeeded at all three locations. Key Points to Identify: - Different resistance profiles at each golf course (Barricade-resistant at courses 1 and 2; simazine-resistant at courses 1 and 3; sulfonylurea-resistant at course 2) - Specticle controlled dinitroaniline-resistant Poa at all sites - Sulfonylurea + simazine combination provided complete control at all three courses - Cost-effectiveness: simazine adds a second mode of action for ~$5/acre

### Review Task 6: New Product Comparison — Halauxifen Formulations

Watch: 55:01 – 1:01:21 Task: McCullough introduces three new products from Dow that all contain halauxifen. Create a comparison noting the other active ingredients in each product, which turfgrass species each is labeled for, and which product would be appropriate for a centipedegrass lawn. Key Points to Identify: - RELZAR: halauxifen + florasulam — all major warm and cool-season species; one labeled rate - Game On: halauxifen + 2,4-D choline + fluroxypyr — primarily cool-season grasses plus bermudagrass and zoysiagrass; NOT centipedegrass or St. Augustinegrass (2,4-D sensitivity) - Switchblade: halauxifen + dicamba + fluroxypyr — warm and cool-season including centipedegrass and St. Augustinegrass - For a centipedegrass lawn: RELZAR or Switchblade, not Game On

## Review Activity Summary

Total Tasks: 6 Coverage Distribution: - Weed Identification (early): Task 1 - Cultural Practices (early-mid): Task 2 - Pre-Emergent Science (mid): Task 3 - Herbicide Resistance (mid-late): Tasks 4, 5 - New Products (late): Task 6

Design Notes: Tasks are structured to guide self-paced viewing by directing learners to specific segments. Each task asks for synthesis beyond simple recall — listing, comparing, tracing progressions, or correcting misconceptions — to promote active engagement with the video content.

Generated for UGA Center for Urban Agriculture / GTBOP Moodle Certificate Course — Weed Science Source: Corrected SRT (Stage 1) — GTBOP_Transcript_2017-11-17_WeedControlTurf.srt (649 blocks)