PNW Poa Annua Eradication Guide

Comprehensive Multi-Season Strategy for 2,000 Sq. Ft. Lawn (JB Sun & Shade: 60% Perennial Ryegrass, 20% Hard Fescue) — 2-Gallon Mix

1. Active Ingredient & Chemical Definitions

Product / Chemical Primary Role & Mode of Action Key Target & Behavior
Ethofumesate 4SC Selective Knockdown & Root Barrier (Post/Pre-emergent)
Disrupts cell division and lipid synthesis in sensitive weed grasses.		 Targets mature Poa annua via foliar and root uptake. Safe on mature Perennial Ryegrass; requires controlled application rates to protect Hard Fescue.
Mesotrione (Tenacity) Foliar Synergist & Bleaching Agent (Post/Pre-emergent)
Inhibits HPPD enzyme, preventing plant carotenoid production.		 Causes chlorophyll destruction ("neon whitening") under sunlight, stopping Poa seedhead development and weakening cell structures.
Prodiamine The "Fall Wall" Barrier (Pre-emergent only)
Inhibits root elongation in germinating seeds.		 Prevents dormant Poa seeds from sprouting in autumn. Prevents any lawn overseeding for 4–6 months post-application.
Non-Ionic Surfactant (NIS) Foliar Adjuvant
Breaks water surface tension.		 Ensures herbicides flatten and adhere to waxy Poa leaves and seedheads rather than rolling off into the soil.
Spray Indicator Dye Visual Marking Agent (e.g., FarmWorks Dye) Provides visual tracking to prevent gaps or double-pass overlaps that could burn sensitive Fescues.

2. Standard 2,000 Sq. Ft. Tank Mix (2-Gallon Carrier)

Calibrated for a 2-gallon total spray volume (1.0 gal / 1,000 sq. ft.). To protect the 20% Hard Fescue component while maintaining lethal control over mature Poa, keep Ethofumesate at the targeted 1.0 fl. oz. / 1,000 sq. ft. rate.

Ingredient Total Container Amount Rate per 1,000 Sq. Ft. Purpose / Operational Note
Water Carrier 2.0 Gallons 1.0 Gallon Calibrated for constant-flow valve output at a steady pace.
Ethofumesate 4SC 2.0 fl. oz. 1.0 fl. oz. Conservative rate to protect Fine/Hard Fescue.
Mesotrione 0.22 fl. oz. (~2 tsp / 6.5 mL) 0.11 fl. oz. Foliar whitening and photosynthetic shutdown.
NIS Surfactant 0.64 fl. oz. (~4 tsp / 19 mL) 0.32 fl. oz. Drives leaf coverage and penetration.
FarmWorks Dye 2.0 fl. oz. 1.0 fl. oz. Hardscape and overlap prevention indicator (adjust higher if needed).

3. Execution & "Spray-Water-Mow" Protocol

[Day -1 to 0] DRY LEAF PHASE → [Hours 0 to 24] FOLIAR ABSORPTION → [Day +1 to +3] SOIL ACTIVATION → [Day +4] MOW & BAG

  1. New Sprayer Calibration Check: Fill with 1 gallon of clean water first to test nozzle spray fan, check for leaks, and verify pace before loading active mix. Ensure that at the 1,000 sq. ft. mark, exactly 1.0 gallon remains in the tank.
  2. Pre-Spray Safety: Wet down adjacent concrete/hardscapes with clean water before spraying. Saturated concrete cannot absorb blue dye. Keep a live garden hose ready for immediate rinsing.
  3. Application Technique: Maintain nozzle height at 18–20 inches off the turf to catch elevated seedheads. Shut off the spray trigger before initiating turns at lawn borders.
  4. Foliar Window (0–24 Hours): Keep the leaf canopy dry for a full 24 hours post-application so Mesotrione fully translocates.
  5. Soil Activation Window (24–48 Hours): Apply fertilizer and water the lawn with 0.25" to 0.5" of water. This moves Ethofumesate into the upper root zone and washes fertilizer into the soil.
  6. Mowing Protocol: Wait 72–96 hours post-spray to mow. Set height to 2.5"–3.0" and bag all clippings to eliminate viable seedheads from the site.

4. Master Seasonal Schedule

Season / Window Herbicide Action Nutrition & Soil Management Operational Objective
Spring Knockdown (April) Ethofumesate (2oz) + Mesotrione (2tsp) Apply balanced slow-release feed (16-4-8 or 20-0-5) at 1.0 lb N / 1,000 sq. ft. Knock down mature Poa, suppress seedheads, and force Perennial Ryegrass recovery.
Spring Cleanup (Mid-May) Ethofumesate (2oz single active) Regular mowing at 3.0"; continue bagging clippings if seedheads persist. Second pass to eliminate lingering Poa root systems before summer heat.
Summer Guard (June–August) Spot-treat escapes with Mesotrione only Foliar Chelated Iron applications for dark green color without surge top-growth. Prevent heat stress on desirable turf while keeping Poa suppressed.
The Fall Wall (Sept 1) Prodiamine (Follow label rate for 2,000 sq. ft.) Apply high-Nitrogen recovery fertilizer (29-0-4 or 32-0-4) at 1.0 lb N / 1,000 sq. ft. Establish total soil barrier against fall-germinating Poa seeds. No overseeding.
Winter Guard (October) Ethofumesate (2oz) Apply High-Potassium Winterizer (10-0-20 or 16-0-24) at 1.0 lb N / 1,000 sq. ft. Root zone protection against winter Poa emergence and cold-weather cell damage.

5. Fertilization Rates & Reseeding Strategy

Fertilizer Calculations (Targeting 1.0 lb N per 1,000 Sq. Ft.)

To calculate product needed for the entire 2,000 sq. ft. area, use:

Pounds of Product = 2.0 / Nitrogen Decimal Percentage

Reseeding & Renovation Window