Webinar Title: The Latest in Nursery Weed Control
Webinar Date: March 12, 2026
Speaker: Dr. Chris Marble, Associate Professor of Horticulture, University of Florida IFAS, Mid-Florida Research and Education Center, Apopka, FL
Moderator: Dr. Shimat Joseph
Duration: 45:13
Series: Green & Commercial
Review Prompts
Review Task 1
Watch: 1:00 – 3:30
Task: Identify the rationale Marble gives for non-chemical weed control options and the types of nursery situations where they are most practical.
Key Points to Identify:
- Herbicide-sensitive species (hydrangea, annuals, perennials) where chemicals cannot be used
- Non-chemical tools as supplements to herbicide programs, not all-or-nothing replacements
- Sanitation, prevention, and rice hull mulch as elements of an integrated approach
Review Task 2
Watch: 3:30 – 8:30
Task: Trace the hand weeding frequency study from its design through the cost savings data. Note the specific protocol that produced the 40–60% reduction.
Key Points to Identify:
- Study design: blocks treated with Tower and Gemini, weeded every two weeks vs. every eight weeks, time and biomass recorded over 24 weeks
- Workers pulled only large weeds likely to seed within two weeks — cotyledon-stage weeds were left
- Cost reduction of 40–60% across sites (65% at the Florida site); blocks weeded three to seven times faster per pass
Review Task 3
Watch: 8:30 – 10:00
Task: Describe how Marble applies the hand weeding frequency research to cleanup protocols at nurseries he consults with.
Key Points to Identify:
- Cleanup approach for heavily infested blocks: remove the largest weeds, apply pre-emergent, scout for breakthroughs, weed again soon
- Training crews to distinguish which weeds to pull (larger than a half dollar) and which to leave (cotyledon-stage)
- The Barker and Neal 2016 publication as the published source for this research
Review Task 4
Watch: 10:00 – 12:45
Task: List the pre-emergent herbicides Marble identifies as having early post-emergence activity and the specific weed species each one controls after emergence.
Key Points to Identify:
- Dimethenamid-P (Tower, FreeHand) on spurge; indaziflam (Marengo) on oxalis, spurge, and annual bluegrass
- Isoxaben (Gallery, Gemini) killing bittercress up to the flowering stage at labeled rates
- Oxadiazon (Ronstar G) on artillery weed; Dimension on oxalis and bittercress; oxyfluorfen products (OH2, Biathlon) on multiple broadleaf species
Review Task 5
Watch: 12:50 – 17:30
Task: Explain the fertilizer placement problem Marble identified with rice hull mulch and why it matters for growers using controlled-release fertilizer.
Key Points to Identify:
- Rice hull properties: lightweight, hydrophobic, small particle size allowing complete surface coverage at lower depths than wood mulch
- Coleus and Vitex growth reduction when fertilizer was top-dressed on two inches of rice hulls vs. incorporated
- Likely mechanism: rice hulls dry quickly, slowing moisture-dependent release from fertilizer coatings
Review Task 6
Watch: 17:30 – 20:00
Task: Summarize what happens when rice hulls are applied over pots that already have emerged weed seedlings, including the threshold depth for effective control.
Key Points to Identify:
- One inch of rice hulls reduced survivability of cotyledon-stage eclipta and Phyllanthus by 95% or more
- Bittercress and oxalis at one inch showed nearly 100% control
- Weed-free pots at application are ideal, but one inch of hulls will kill most small seedlings already present
Review Task 7
Watch: 20:00 – 24:00
Task: Compare what happened when weed seeds were placed above vs. below the rice hull layer, and note the outdoor degradation rate Marble reported.
Key Points to Identify:
- Seeds on top of rice hulls: 89% control over 12 weeks across five outdoor species (doveweed, crabgrass, spurge, eclipta, Phyllanthus)
- Seeds below the rice hulls: growth similar to non-mulched controls — hulls do not physically block emergence from below
- Degradation: about 40% of applied layer remaining at 12 months; hulls matched pre-emergent rotations for six months before losing effectiveness
Review Task 8
Watch: 24:00 – 27:20
Task: Explain the substrate stratification concept Marble adapted for weed control and the specific results he reported for liverwort and bittercress.
Key Points to Identify:
- Stratified containers: coarser bark on top (low moisture, no fertilizer), finer substrate with fertilizer below
- Liverwort eliminated for over 20 weeks — it requires both nitrogen and moisture at the surface, which stratification removes
- Bittercress reduced by 40–60% with stratified treatments; Jeb Fields (UF) credited with the original stratification concept
Review Task 9
Watch: 27:20 – 30:00
Task: Outline the step-by-step process Marble describes for building a herbicide rotation using the 2017 Southeast Pest Management Guide.
Key Points to Identify:
- Start with the guide to identify which herbicides are labeled for the grower’s ornamental species (gardenia example)
- Group labeled options by mode of action — avoid pairing herbicides from the same group as rotation partners
- Match herbicide choices to the worst weed species by season (e.g., spurge pressure in May–July drives the selection of FreeHand or Marengo for that window)
Review Task 10
Watch: 30:00 – 36:30
Task: Identify the two new bare-ground herbicides Marble discussed and then compare the LEAP project equipment efficiency data for granular vs. liquid applications.
Key Points to Identify:
- StrataCor (pethoxamid, SePRO) for broadleaf/grass/sedge; SureGuard Extra (flumioxazin + pyroxasulfone) for broadleaf/grass with longer residual than SureGuard alone
- Granular: 3 employees, 5 hours, 1.3 acres, $5,500 chemical cost; Liquid boom: 1 employee, 6 hours, 17 acres, roughly half the chemical cost
- Higher liquid application volumes (up to 200 gal/acre) increase canopy penetration but require more time and water
Review Task 11
Watch: 36:30 – 40:00
Task: Note the drone application data Marble presented and his call for collaborators on the LEAP project.
Key Points to Identify:
- Drone covered a half acre in three minutes at 200 lbs/acre (two passes, 100 lbs per hopper load)
- Marble still seeking growers to allow baseline equipment efficiency measurements during normally scheduled applications
- UF weed management training course: four weeks, eight lessons, offered in English and Spanish
Review Task 12
Watch: 40:00 – 45:00
Task: Compare the weed control mechanisms of rice hull mulch and wood/bark mulch as discussed in the Marble–Bartley Q&A exchange.
Key Points to Identify:
- Bartley’s master’s research found wood/bark mulch controlled weeds better when seeds were placed under the mulch; Marble’s data showed rice hulls worked better when seeds landed on top
- Wood and bark mulches suppress by physical weight — too heavy for seedlings to push through
- Rice hulls suppress by moisture deprivation — they dry rapidly and prevent seed germination on the surface, but are too lightweight to block emergence from below
Review prompts produced for UGA Center for Urban Agriculture / GTBOP Archives
Source: Corrected SRT (Stage 1) — GTBOP_Transcript_2026-03-12_NurseryWeedControl.srt (670 blocks)
Archive Package (Stage 2) — GTBOP_Archive_Summary_2026-03-12_NurseryWeedControl.md