Southern Naiad Control Methods
Updated: Aug 9
Hello fellow Pondologists, and welcome to the fourth episode of “Pond Weed Problems”!
It starts as a great habitat for your fish, and ducks love it because it is a native plant that belongs there. But under the right conditions, this "good guy" can turn into a silent killer overnight. Managing Southern Naiad is like walking a tightrope: if you try to cut it, you trigger fragmentation and spread the infestation; if you spray it in muddy water, your chemicals might be instantly deactivated; and if you kill too much of it at once, you risk a massive oxygen crash that can wipe out your fish.
Today, we are disarming the ticking time bomb known as Southern Naiad by walking you through the entire playbook—from identification and water testing to the exact chemical cocktails you need to control it safely.
Note: Always check with your local laws and regulations before using any recommended treatment options.
1. The Ecology and Identification of Southern Naiad
Southern Naiad (Najas guadalupensis), also known as bushy pondweed, is a native submerged aquatic plant found throughout North and South America. In moderation, it is an excellent plant that provides habitat for invertebrates, cover for small fish, and a primary food source for waterfowl. It only becomes a weed when it grows so rapidly and densely that it chokes out other plants, interferes with recreation, and poses a risk to dissolved oxygen levels.
Identifying Southern Naiad vs. Look-Alikes
Proper identification is critical because Southern Naiad is frequently confused with other submerged plants.
Table 1: Identification Guide
Feature | Southern Naiad (Native) | Brittle Naiad (Invasive) | Coontail (Native) | Chara (Macroalgae) |
Plant Type | Submerged Plant | Submerged Plant | Submerged Plant | Macroalgae |
Roots | Rooted | Rooted | No roots | Rhizoids (root-like) |
Leaf Structure | Simple, strap-like leaves | Simple, strap-like leaves | Forked / Branched | Bristly, stem-like branches |
Leaf Margin | Microscopic teeth (need hand lens) | Visible teeth (no lens needed) | Smooth (but leaves are forked) | N/A |
Feel in Hand | Smooth, pliable | Stiff, brittle, spiny | Rough, spiny, stiff | Gritty, crusty |
Smell | No distinct smell | No distinct smell | No distinct smell | Musky odor when crushed |
The Drivers and Problems
● Nutrients & Clarity: Overabundant growth is a sign of excessive nutrients, shallow depths, and clear water. Ponds with high visibility and low average depths are particularly prone to dense, choking mats.
● The Clogging & Crashing Problem: Dense mats interfere with fishing, boating, and swimming. Furthermore, when this massive volume of plant matter dies off in the fall or winter, bacterial decomposition consumes dissolved oxygen, which can cause an oxygen crash and kill your fish.
● Reproduction: Southern Naiad dies back annually but sprouts from a heavy seed bank, and it spreads aggressively during the growing season through fragmentation (every cut piece can drift away and propagate new plants).
2. Pre-Treatment Assessment
Before applying any chemical, you must perform a thorough pre-treatment assessment to prevent user error and accidental fish kills.
● Step 1: Calculate Pond Volume: Because you are treating the entire water volume, you must measure in acre-feet. (Formula: Surface Acres X Average Depth = Acre-feet).
● Step 2: Water Chemistry Testing: Test your water to see which chemicals have a "right of way" to work:
○ The Diquat Test (Turbidity): Muddy or murky water will bind to and deactivate Diquat on contact.
○ The Flumioxazin Test (pH): If your pH is above 7.5, Flumioxazin will degrade too rapidly and result in poor control.
○ The Komeen Test (Alkalinity): Test your alkalinity before using this copper complex; levels below 50 ppm create high risks for copper-sensitive fish like koi and trout.
○ The Fluridone Test (Water Exchange): Fluridone requires 30 days of contact time and will fail in ponds with constant inflow and outflow.
3. A Comparative Analysis of Southern Naiad Control Methods and Herbicides
Treatment requires delivering the herbicide into the water column using either fast contact herbicides or slow systemic herbicides.
Table 2: Herbicide Breakdown
Herbicide (Active Ingredient) | Type | Speed of Action | Efficacy Rating (S. Naiad) | Key Limitation / Requirement |
Diquat | Contact | Very Fast (1-7 Days) | Excellent | Ineffective in muddy or turbid water. |
Endothall (Dipotassium Salt) | Contact | Fast | Excellent | Must use Dipotassium salt (Aquathol®); Amine salt is toxic to fish. |
Flumioxazin | Contact | Fast | Excellent | Ineffective in high-pH water (>8.5). |
Fluridone | Systemic | Very Slow (30-90 Days) | Excellent | Ineffective in ponds with water exchange/outflow. |
Penoxsulam | Systemic | Slow (2-4 Weeks) | Good | Requires sufficient contact time; rapid dilution reduces efficacy. |
4. Field Guide to Application and Safety
● Application Techniques: In water deeper than 3 feet, use subsurface injection (pumping diluted chemicals via weighted hoses directly into weed beds) or granular application (broadcasting pellets so they sink to the lower stems). Surfactants are generally not required since you want the herbicide to disperse into the water column.
Recommended Application Rates:
○ Komeen: Add 5 to 10 gallons per acre in a 50-gallon tank (or 1 to 2.5 gallons for a 4-gallon backpack sprayer depending on density).
○ Diquat: Use a standard rate of 2 gallons per acre in a 50-gallon tank (or 24 ounces in a backpack sprayer).
○ Komeen + Diquat Combination: A highly effective cocktail. Mix 5 gallons of Komeen and 2 gallons of Diquat per acre in a large tank (or 1 gallon of Komeen and 24 oz of Diquat for a backpack setup).
○ Fluridone: Apply as a whole-lake treatment to reach at least 45 ppb, ensuring no continuous flow-through.
Managing the Primary Risk: Oxygen Depletion
Fast-acting contact herbicides cause rapid plant decay, leading to bacterial oxygen consumption and potentially fatal fish kills.
● The Golden Rule: NEVER treat your entire pond at once with a fast-acting contact herbicide. Treat only 1/4 to 1/3 of the pond at a time, waiting 10-14 days between sections for oxygen levels to recover. (Fluridone is the sole exception due to its slow, gradual 30-to-90-day kill).
Water Use Restrictions
Always read the label, as restrictions vary widely. Swimming and fishing generally have 0-day restrictions with modern herbicides, but irrigation and livestock watering windows vary significantly (e.g., Fluridone requires a 7 to 30-day irrigation hold).
5. Alternative & Complementary Management Practices
● Nutrient Mitigation: Address the root cause of excessive nutrients by reducing fertilizer applications, maintaining septic systems, and creating unmowed vegetative "buffer strips" around the edge to filter runoff.
● Aquatic Dyes: Blue or black dyes shade the water column and block sunlight, acting as an excellent preventative tool when applied early in the spring.
● Physical Removal: Manual raking or cutting is intensely labor-intensive, and because Southern Naiad reproduces heavily from fragments, leaving cut pieces behind will actively spread the infestation. You must meticulously remove all fragments if you choose this route.
● Grass Carp: Results are mixed because grass carp are picky eaters that will target preferred plants like American Pondweed before touching Southern Naiad. If stocked, use only sterile, triploid carp with proper state permits at a rate of 6 per littoral acre (shallow areas 6 feet deep or less).
Remember, Southern Naiad is a native plant. The goal should never be eradication, but control. By addressing the root causes of nutrient pollution and using smart, preventative measures, you can keep this plant in balance.
If you're more of a visual learner (like myself) click on the link below to watch the video version of this!
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