4.4 Preharvest, Restricted-Entry, and Reentry Intervals

Two Intervals, Two Purposes

PHI and REI are both label-driven waiting periods, but they protect different things and apply to different people. Confusing them is a common Iowa exam error.

A field can be past its REI (workers may enter freely) but still inside its PHI (the crop cannot yet be harvested), or the reverse. Always check both numbers.

Preharvest Interval (PHI)

The Preharvest Interval (PHI) is the minimum number of days between the last pesticide application and harvest of the crop. It is set so residues fall below the tolerance (the maximum legal residue level, established by EPA under FIFRA Section 408). Harvesting before the PHI expires risks an illegal residue violation, crop condemnation, and a label-violation citation.

'Harvest' includes direct-combining, cutting (swathing), and — for forage crops — grazing. For animal feed crops, labels use separate terms:

• Pregrazing Interval (PGI): days between application and allowing livestock to graze.
• Feeding restrictions: days before cutting hay, silage, or straw, or before feeding treated forage.

Example: a label might say 'Do not graze or feed green forage for 14 days after application. Do not harvest for hay for 30 days.' Each is a separate restriction that must be met.

When Tank-Mixing, Use the Longest PHI

If you apply a tank mix of two products with different PHIs, you must wait the longest PHI among them before harvest. The same rule applies to REIs. A shorter PHI does not override a longer one.

Restricted-Entry Interval (REI)

The Restricted-Entry Interval (REI) is the time after a pesticide application during which entry into the treated area is restricted under EPA's Worker Protection Standard (WPS, 40 CFR Part 170). The REI appears on the label in the Agricultural Use Requirements box. During the REI:

• Workers may not enter the treated area for hand-labor tasks.
• Only exempt entries are allowed (see below).
• Posted warning signs or oral notification may be required.

Typical REIs are 12, 24, or 48 hours, but some products carry longer REIs (for example, 5 days for certain organophosphates with dermal toxicity concerns). The REI is set based on the product's acute dermal and inhalation toxicity.

REI vs. Signal Word

A common misconception is that the signal word sets the REI. It does not. The REI is determined by the product's acute dermal and inhalation toxicity and by EPA's WPS rules. A CAUTION product can carry a 48-hour REI; a WARNING product can carry a 12-hour REI. Read the label's Agricultural Use Requirements box for the actual REI.

Early-Entry Exceptions Under WPS

The WPS allows a few narrow exceptions for entering during an REI. Iowa agricultural employers must meet all conditions of any exception they use.

No-Contact Exception

A worker may enter if they will have no contact with anything treated (soil, water, air, plant surfaces) and any inhalation exposure level on the label has been reached. No special PPE is required.

Short-Term Activities Exception

• No hand labor.
• No more than 1 hour in any 24-hour period.
• No entry during the first 4 hours after application, and until any inhalation criterion is met.
• Early-entry PPE from the label must be provided and worn.

Limited-Contact / Irrigation Tasks Exception

• No hand labor.
• No more than 8 hours in any 24-hour period.
• No entry during the first 4 hours after application, and until any inhalation criterion is met.
• Contact is minimal (feet, lower legs, hands, forearms).
• The need for entry could not have been foreseen, and delay would cause significant economic loss.
• Does not apply to products whose labeling requires double notification (both posted signs and oral warning).
• Early-entry PPE must be provided and worn.

Agricultural Emergency Exception

A state, tribal, or federal agency must declare an agricultural emergency. Hand labor is permitted, and there is no time limit, but all PPE, training, and decontamination requirements of the short-term exception apply.

Double Notification

Some labels require double notification — both a posted warning sign at the entrance to the treated area and an oral warning to each worker — before and during the REI. A label that requires double notification does not allow the limited-contact/irrigation exception. The label's Agricultural Use Requirements box states whether notification is oral, posted, or both.

Plant-Back (Rotational Crop) Intervals

A plant-back interval (also called a rotational crop interval) is the minimum time that must pass after a pesticide application before a different crop can be planted in the same field. Planting too soon can injure the rotational crop or cause illegal residues in it.

Example: a label may say 'Do not plant rotational crops for 4 months after application. Corn, soybeans, and wheat may be planted 4 months after application; all other crops 18 months.' Plant-back intervals are distinct from PHI and REI — they govern what you can plant next, not when you can harvest or enter.

Putting It Together

Before any application, read the label for three waiting periods: the PHI (when you can harvest or graze), the REI (when workers can re-enter), and any plant-back interval (when you can rotate to the next crop). Note the longest interval when tank-mixing. For WPS-covered agricultural establishments, check the notification requirement and whether double notification removes the limited-contact exception. Meeting these intervals is part of using the product consistent with its labeling — and therefore part of complying with FIFRA and Iowa Code Chapter 206.