When the Dealer, the Label, and the SDS Disagree
A grower hands you two jugs and a 500-gallon tank for 80 acres of field corn. Product A's label states a rate of 1.5 to 2 pints per acre, then in the same directions section: 'Do not apply with sprayable fertilizer solutions,' 'Do not make more than two applications per season,' and 'Do not tank mix with any product containing active ingredient B.' Product B's label permits tank mixing with liquid nitrogen and does not mention A. The dealer's written recommendation says to load both products plus 28% UAN into the same tank and apply at 15 GPA. The SDS for Product A lists a diluted pH of 9.5 and warns in Section 10 about contact with oxidizing agents. The grower wants to start at 6 a.m. to beat the afternoon wind and asks you to hurry.
1. Which document controls here, and what do you do with the dealer's recommendation? Explain the reasoning and the consequences of each possible choice.
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The label controls. Under FIFRA it is unlawful to use a pesticide in a manner inconsistent with its labeling, and a dealer recommendation cannot authorize what a label prohibits. An SDS is a hazard-communication document - it explains pH, incompatibility, and first aid - but it is not a source of use directions and never overrides the label. Where A's label forbids sprayable fertilizer and forbids any product containing active B, both parts of the dealer's recipe are off-label.
Consequences of going ahead: the applicator, the grower, and arguably the dealer share exposure - misbranding and use-inconsistent-with-label findings, potential crop injury, and no registrant support if the tank plugging or crop damage is traced back. Records of an off-label mix are discoverable, and the dealer's written note becomes evidence.
What to do: do not mix. Hold the job, tell the grower plainly which sentence blocks the mix, and work out an alternative - apply A alone and place B separately, or substitute a formulation of B that A's label permits, if one exists. Confirm any substitution in writing with the registrant's technical representative, keep the label and the written recommendation in the job file, and record the decision. Also note the season cap of two applications: if A was already applied twice, no rate makes the job legal.
2. Assume the fertilizer is dropped and A plus B are still on the table. Describe how you would verify compatibility and physically load the tank, and work out the quantities for 80 acres.
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Quantities. 80 acres x 2 pt = 160 pt = 20 gallons of product total (10 gallons of each if rates are equal - confirm B's rate separately). At 15 GPA a 500-gallon tank covers 33.3 acres, so 80 acres needs three loads (two full, one partial of about 13.4 acres). A full load carries 33.3 x 2 pt = 66.6 pt = 8.3 gallons of A.
Compatibility. Even with a label-permitted pair, the high pH (9.5) and the Section 10 note make a jar test mandatory, not optional: same water source, same concentration ratios, same order, in a clear quart jar, capped and inverted ten times, then observed at 5, 30, and 60 minutes for cream, flakes, oily film, heat, or a layer that will not redisperse. Do the test at the water temperature you will actually use at 6 a.m.
Loading order. Half-fill with water and start agitation; add dry or water-dispersible formulations first, then liquid flowables, then emulsifiable concentrates, then adjuvants; top off and keep agitation running. Never put two concentrates in the tank together before dilution - that is where most incompatible mixes actually form.