A herbicide label is a legal document, not just packaging — every abbreviation and warning on it exists to tell you something specific and actionable. Here's what the most commonly misunderstood terms actually mean.
Key Terms, Defined
- REI (Re-Entry Interval)
- The minimum time that must pass after application before people or pets can safely re-enter the treated area without protective equipment. This is a legal minimum based on toxicology data, not a suggestion.
- PHI (Pre-Harvest Interval)
- Relevant for edible crops — the minimum time that must pass between the last herbicide application and harvest. This ensures residue levels have dropped to a safe threshold before consumption.
- Signal Word
- A required label term indicating relative toxicity: "Caution" indicates the lowest toxicity category, "Warning" indicates moderate toxicity, and "Danger" indicates the highest toxicity category requiring the most careful handling.
- Active Ingredient
- The specific chemical compound responsible for the herbicide's effect, usually listed by percentage, distinct from inert ingredients that make up the rest of the formulation.
- Rainfastness
- The time needed after application before rain will no longer significantly reduce effectiveness, since sufficient absorption has occurred by that point.
- Non-Selective / Selective
- Whether the product kills all vegetation it contacts (non-selective) or specifically targets certain plant types while sparing others (selective).
Pro tip: The signal word alone tells you more at a glance than almost any other single label element. If you're comparing two products and only have a moment to check relative caution needed, the signal word ("Caution," "Warning," or "Danger") is the fastest legitimate indicator.
Signal Words at a Glance
| Signal Word | Relative Toxicity | What It Means for You |
|---|---|---|
| Caution | Lowest category | Standard precautions generally sufficient |
| Warning | Moderate | More careful handling and PPE recommended |
| Danger | Highest | Strict handling precautions required |
Where to Find the Full Picture
The Safety Data Sheet (SDS) that accompanies every properly sold herbicide expands on everything summarized on the front label — exact REI and PHI figures, storage requirements, and emergency response information. Every product on Herbi Solutions, including our Ammonium Glyphosate 15% and Glufosinate 10% SL, ships with a full SDS.
Watch out: REI and PHI are two different numbers measuring two different things — don't confuse a product's re-entry interval (safe for people/pets to walk on the area) with its pre-harvest interval (safe to harvest and eat a treated crop). Mixing these up on an edible planting is a genuine food safety concern, not just a technicality.
Frequently Asked Questions
What does REI mean on a herbicide label?
REI stands for Re-Entry Interval — the minimum time that must pass after application before people or pets can safely enter the treated area without protective equipment.
What's the difference between REI and PHI?
REI covers safe re-entry to the treated area in general; PHI specifically covers the minimum time before harvesting and consuming a treated edible crop — they're different intervals measuring different risks.
What does the signal word "Caution" mean on a herbicide label?
"Caution" indicates the lowest toxicity category among the three required signal words, though standard safe handling practices still apply.
Every product on Herbi Solutions ships with a complete label and Safety Data Sheet — browse our range to see the full details before you buy.