Glyphosate vs. 2,4-D vs. fluridone: aquatic herbicide comparison
Three of the most-used aquatic herbicides in US lake management. They are not interchangeable — each is matched to a specific problem and using the wrong one wastes the money and worsens the lake.
| Attribute | |||
|---|---|---|---|
| Type | Non-selective systemic | Selective systemic broadleaf | Systemic submerged |
| Mode of action | Inhibits EPSP synthase (amino acid synthesis) | Auxin mimic (causes uncontrolled growth) | Inhibits carotenoid synthesis (photo-bleaching) |
| Best for | Emergent and floating broadleaf plants (hyacinth, lettuce, cattails, torpedograss) | Water hyacinth, water lettuce, Eurasian milfoil | Hydrilla, Eurasian milfoil, other submerged invasives |
| Speed of result | 10–21 days for visible die-off | 7–14 days for visible die-off | 30–60 days for full effect |
| Application method | Foliar spray (must contact above-water foliage) | Foliar spray or granular | Whole-water-body application; pellet or liquid |
| Selectivity | None — kills any plant the spray contacts | Spares grasses and most monocots; kills broadleaves | Damages most submerged natives at typical rates |
| Resistance reported | Yes, in some torpedograss populations | Limited | Yes, in repeated-treatment Florida hydrilla populations |
| Common brand names | Rodeo, AquaMaster, AquaPro | DMA 4 IVM, Navigate, Sculpin G | Sonar, Avast!, Whitecap |
Frequently asked questions
Will glyphosate kill hydrilla?
No. Glyphosate is a foliar contact herbicide and hydrilla foliage is below the waterline. Use fluridone or endothall for submerged invasives.
Is 2,4-D safe for fish?
At labeled aquatic application rates, yes — 2,4-D has very low fish toxicity. The fish-kill risk comes from the oxygen crash after the treated vegetation decays, not the herbicide itself.
Why does fluridone take so long?
Fluridone is a systemic that works by inhibiting carotenoid synthesis — the plant photobleaches, depletes its energy reserves, and dies over weeks. The slow timeline is the mechanism, not a problem.