If I mix two products in one tank, is that one spray record or two?

Two. Each product going through the boom is its own active ingredient, with its own rate, its own lot number, and its own pair of intervals, and each needs its own line in the record even though they left the nozzle together in the same pass, on the same date, at the same field. One tank, one pass, one date — but as many product entries as products in the tank.

Which re-entry or pre-harvest interval applies when two products are in the same tank?

Whichever product's interval is longer. The block or field is not clear for re-entry, and the crop is not clear for harvest, until every product in that tank's own interval has passed for that application. The more restrictive number governs the whole tank, not an average and not the shorter one, and that has to be a comparison someone actually makes and writes down — not an assumption that a legal tank mix means a single, simpler interval.

Can I legally mix any two labelled products together?

Not automatically. Whether two products may be tank-mixed at all, and under what conditions, is itself governed by the labels of both products and, in many jurisdictions, by the regulator — mixing compatibility and the resulting interaction between active ingredients is a separate question from whether each product is individually labelled for the crop. That determination belongs to the label and the regulator, not to a rule of thumb about products that have been mixed before without incident.

Do I need to record the order the products were added to the tank?

It is good practice to, because mixing order affects both physical compatibility in the tank and, occasionally, how a label's own instructions describe combination use. It costs nothing to write down and can matter if a tank mix behaves unexpectedly — settling, clumping, or reduced efficacy — and someone later needs to reconstruct exactly what went into the sprayer and in what sequence.

Tank Mix Spray Recordkeeping

Tank-mixing is ordinary practice: two products, sometimes three, go into the same tank so one pass across the field does the work of two. It saves fuel, time, and soil compaction, and most operations do it routinely. What it does not do is save a record. A pass with two products in the tank produces two obligations, not one, and the shortcut that makes the spraying efficient is exactly the place a record most often gets flattened into something less than it needs to be.

The instinct is to write the pass down the way it felt — one trip across the field, one line in the log. But the tank does not decide what the record has to contain. The label does, for each product in it, separately. This page is about why a single pass with a mixed tank still needs a record for every product it carried, and about the one part of a tank mix that is genuinely different from spraying one product at a time: figuring out which constraint governs.

The label is the authority. Nothing here states a re-entry interval, a pre-harvest interval, or a mixing compatibility rule for any product or combination, and you should distrust anything that does. Those are set by each product's label, and by the regulator and certifier who govern your operation; they vary by product, by combination, by rate, and by jurisdiction. What follows describes the process of recording a tank mix correctly. For the intervals and the mixing rules themselves, read both labels and ask your regulator.

One tank, one pass, and more than one record

Say a fungicide and an insecticide go into the same tank for a single pass across a block. Physically, that is one event: one fill, one trip down the rows, one nozzle setting. On paper, it is two products, each with its own active ingredient, its own rate, its own lot number, and its own pair of intervals — and each of those needs its own entry in the record, even though the date, the field, and the equipment are identical across both.

This is not bureaucratic doubling for its own sake. A residue investigation, a drift complaint, or a certifier's audit reaches for one product at a time — "what was the rate of the fungicide," not "what was in the tank." A record that merges two products into one line loses exactly the information that question needs, and there is no way to reconstruct which portion of a blended rate belonged to which active ingredient after the fact.

The more restrictive interval governs the whole tank

Here is the part that is genuinely different about a mixed tank. Each product carries its own re-entry interval and its own pre-harvest interval from its own label, and those two numbers, for two different products, are very often not the same length. The block or the field is not clear for re-entry, and the crop is not clear for harvest, until the longer of the two intervals has fully elapsed — not the shorter one, and not some average between them.

Say, hypothetically, one product in the tank carries a re-entry window measured in a small number of hours and the other carries one measured in a full day. A worker who checks only the shorter number and walks the block after it clears is still inside the second product's window, and the label they didn't read is no defense. The record has to make this comparison explicit — both intervals, both end dates, and a note of which one is later and therefore controls — rather than leaving it as arithmetic to be done under pressure by whoever is standing at the edge of the field deciding whether to send a crew in.

Compatibility is a separate question from either label alone

Being able to combine two products in a tank is not implied just because each is separately labelled for the crop being sprayed. Physical compatibility — whether the two formulations mix cleanly without settling, clumping, or degrading — and legal compatibility — whether either label restricts or prohibits combination with other active ingredients — are both determined by the labels themselves and, in many jurisdictions, by additional guidance from the regulator. A combination that has "always worked before" on a particular farm is not the same thing as a combination the labels actually permit.

This is a decision to make and record before the tank is filled, not something to reconstruct afterward if a problem shows up. Note which products were combined, in what order they were added, and on what basis the combination was judged permissible — the label language, a manufacturer's compatibility chart, or guidance from your regulator. If a tank mix behaves badly — reduced efficacy, visible incompatibility, crop injury — that note is what lets anyone reconstruct what actually happened in the tank.

What a tank-mix record has to contain, product by product

Each product and its active ingredient, with its own rate and its own lot number — never a combined or averaged figure.
The shared facts — field or block, date and time, applicator, equipment — recorded once, since they are genuinely common to the pass.
Each product's re-entry and pre-harvest interval, with the calendar date each resolves to.
The governing dates, flagged explicitly as the later of each pair — the actual date the block clears and the actual date the crop may be harvested.

This is the same field-level detail described in what belongs in a spray record, applied twice in the same breath. A tank mix does not lower the bar for either product — it raises the bar for the record, because now two of everything has to be captured from one pass.

Where this fits with the rest of the input record

A mixed tank is not the only place multiple constraints stack — a biological input added alongside a conventional product runs into the same governing-interval logic, and the broader spray and input records cluster covers the single-product case this page builds on.

Farm40 lets you log more than one product against a single application event, with the active ingredient, rate, lot number, and both intervals as separate fields per product, and it computes the end date for each product from what you enter. Its limit is the same one that applies everywhere on this site: it will compute a correct end date from an incorrect interval just as faithfully as from a correct one, and it does not itself decide which product's interval governs — that comparison is still a judgment a person has to make and confirm. What it removes is the need to reconstruct, weeks later, which of two numbers was actually the later one.

The discipline that makes a tank mix's paperwork trustworthy is simple to state and easy to skip under time pressure: write down every product that went in the tank, not just the one that comes to mind first, and write down which interval, of the several now running, is the one that actually has to clear before anyone acts.

Frequently asked questions

If I mix two products in one tank, is that one spray record or two?: Two. Each product going through the boom is its own active ingredient, with its own rate, its own lot number, and its own pair of intervals, and each needs its own line in the record even though they left the nozzle together in the same pass, on the same date, at the same field. One tank, one pass, one date — but as many product entries as products in the tank.
Which re-entry or pre-harvest interval applies when two products are in the same tank?: Whichever product's interval is longer. The block or field is not clear for re-entry, and the crop is not clear for harvest, until every product in that tank's own interval has passed for that application. The more restrictive number governs the whole tank, not an average and not the shorter one, and that has to be a comparison someone actually makes and writes down — not an assumption that a legal tank mix means a single, simpler interval.
Can I legally mix any two labelled products together?: Not automatically. Whether two products may be tank-mixed at all, and under what conditions, is itself governed by the labels of both products and, in many jurisdictions, by the regulator — mixing compatibility and the resulting interaction between active ingredients is a separate question from whether each product is individually labelled for the crop. That determination belongs to the label and the regulator, not to a rule of thumb about products that have been mixed before without incident.
Do I need to record the order the products were added to the tank?: It is good practice to, because mixing order affects both physical compatibility in the tank and, occasionally, how a label's own instructions describe combination use. It costs nothing to write down and can matter if a tank mix behaves unexpectedly — settling, clumping, or reduced efficacy — and someone later needs to reconstruct exactly what went into the sprayer and in what sequence.