With another growing season upon us, most of the annual applications of crop protection products will happen over the next few months. Product re-evaluation decisions of this past year resulted in big changes to restricted-entry intervals (REI) and pre-harvest intervals (PHI) for some products. The crop protection column has taken a different format this month to address some common questions regarding REI and PHI.

Restricted Entry Intervals

A restricted-entry interval (REI) is the period of time that farm workers, or anyone else, must not perform tasks in treated areas after a crop protection product has been applied. This time allows residues and vapours to dissipate to safe levels for work to be performed. The product label may specify a number of different REIs depending on the crop or activity.

Where does the label REI come from?

The REI found on a product label is specified by the Pest Management Regulatory Agency (PMRA) during its review based on several factors. It is not supplied by a registrant during product registration.

What factors influence the length of an REI?

The calculation of an REI involves many factors such as product rate, number of applications, application interval, crop, and the specific activity. Certain activities involve higher contact with the treated crop which results in a longer REI being applied for these activities.

What happens if there is no REI on the product label?

Some product labels do not have an REI indicated for all or some of their registered uses. If no REI is specified on the product label, the minimum REI of 12 hours applies.

Can anyone enter a treated area before the REI is finished?

There are specific restrictions for early restricted-entry to a treated area. No one can enter a treated area for the first four hours after an application. After four hours, a certified applicator can enter a treated area using the same personal protection equipment (PPE) as the mixer/loader as required on the product label plus a respirator. No hand labour activity can be performed during this time, however, short term entry for operation, movement, or repair of field equipment such as irrigation and frost protection is permitted. This early restricted-entry is limited to one hour in any 24-hour period. 

If an REI is longer than 12 hours, anyone can enter a treated area after 12 hours without PPE unless otherwise required on the product label. However, activities involving contact with the treated crop or soil cannot be performed until the specified REI is complete.

Can the REI on the product label be reduced?

It can sometimes be possible to have a shorter REI approved on a product label. This will usually require a change in the product use pattern or the generation of new data supporting a lower REI. New data supporting a specific crop factor for high-density orchards is one example that has resulted in lower REIs on some product labels.

Pre-harvest intervals

The pre-harvest interval (PHI) is the minimum amount of time between the last application of a crop protection product and when the crop can be harvested. The PHI ensures that residues in the treated crop will not exceed the maximum residue limit (MRL) at harvest.

Why are the REI and PHI so different on some product labels?

As the REI is based on the protection of people performing tasks in the crop while a PHI exists to respect MRLs at harvest, the duration of these intervals can sometimes be quite different. 

What happens if the REI for harvesting and the PHI are not the same on the label?

When the REI for hand or machine harvesting and the PHI are different, the longer of two intervals must be followed to ensure that both protection of people working as well as residue limits are achieved.

What happens if there is no PHI on the product label?

Some product labels do not have a PHI indicated for all or some of their registered uses. If no PHI is specified on the product label, then a crop may be harvested at its maturity without delay. This can result when residues are not expected to be found on the crop following product application. Herbicide treatment prior to crop emergence is one example where this sometimes occurs. Even if no PHI is specified on the label, any REI restrictions for harvesting must still be followed. 

Can the PHI on the product label be reduced?

It can sometimes be possible to have a shorter PHI approved on a product label. This will often require new residue data indicating the new use pattern will still respect MRLs.