Calibration, Tank Mix, and a Spill at the Loading Pad
The Mendez farm runs a 500-gallon pull-behind sprayer with 24 nozzles on 20-inch spacing (a 40-foot boom). The plan is 20 GPA at 4.5 mph, tank-mixing Product A at 1.5 pt/acre, Product B at 8 fl oz/acre, and a nonionic surfactant at 0.25% v/v. Product A's label warns not to tank mix with products containing a named active ingredient and recommends a jar test; Product B's label requires a 1/4-inch rainfall-free window and lists a 12-hour REI. During loading, a 2.5-gallon jug of Product B tips over and about 1 gallon of concentrate pours onto the gravel pad. The pad drains toward a drainage swale 30 feet away, and a domestic wellhead sits 60 feet upslope. The nozzle catch jar is in the shop, and the tank already holds 250 gallons of water.
1. Calculate the required per-nozzle flow and the amount of each product for a full tank, and explain how to verify the rate in the field.
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Use the standard nozzle-flow relationship: gallons per minute per nozzle = (GPA x mph x nozzle spacing in inches) / 5940.
- Per nozzle: (20 x 4.5 x 20) / 5940 = 1800 / 5940 = 0.303 gpm
- Total boom flow: 24 x 0.303 = 7.27 gpm
Tank capacity in acres: 500 gallons / 20 GPA = 25 acres per tank.
- Product A: 25 x 1.5 pt = 37.5 pt = 4.69 gal, i.e. about 4 gal + 2 qt + 24 fl oz
- Product B: 25 x 8 fl oz = 200 fl oz = 1.56 gal, i.e. 1 gal + 2 qt + 8 fl oz
- Surfactant at 0.25% of 500 gal = 1.25 gal (5 qt)
Verification: catch one nozzle for 60 seconds and compare to 0.303 gal (about 39 fl oz). More than roughly 5% high or low means worn or partially plugged tips - replace, do not compensate by changing pressure. Also confirm speed with a timed run over a measured course, and remember that if the actual speed is 5 mph rather than 4.5, the applied GPA drops by about 10% below the target even though all the arithmetic above was correct.
2. How do you handle Product A's tank-mix restriction and the jar test before anything goes in the tank?
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Label language controls, and the jar test is cheap insurance against a ruined 500-gallon load.
Restriction first: read Product A's prohibition against the named active ingredient and check Product B's label for that same active ingredient (and check Product B for its own mixing prohibitions). If Product B contains it, the two cannot go in the same tank - no jar test overrides a label prohibition. Options then are separate applications with a fully cleaned tank, or substituting a compatible partner product.
If there is no prohibition, run the jar test: use a clean quart jar with the same water source you will spray, add the products at the same ratio as the tank (scaled down: the surfactant rate is a fraction of a drop, so use a measured dilute stock), invert ten times, and observe for 15-30 minutes. Look for flocculation, clumping, oily separation, sediment, or heat. Any of those means incompatible - do not load.
Mixing order if compatible: fill to about half with water, add dry formulations (wettable powders, dry flowables) first, then liquid flowables, then emulsifiable concentrates, then solutions, and the surfactant last, with agitation throughout. With 250 gallons already in the tank, you are mid-fill; add products in that order while continuing to fill, rather than dumping everything into the last 10 gallons.
3. Walk through the spill response for the gallon of Product B concentrate, including the well and the swale.
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Treat a concentrated pesticide spill near a well and a drainage swale as a containment emergency.
Protect people first: stop and put on the label-required PPE - chemical-resistant gloves, goggles, apron, and boots. Keep other workers out of the area and do not allow anyone to kneel in the puddle.
Stop and contain: right the jug and close it. Build a berm of absorbent or dry soil between the puddle and the swale so nothing reaches surface water, and keep the material downslope of the wellhead rather than flushing it toward it. Do not hose the pad down - water spreads the product and turns a small spill into a water-quality event.
Clean up: absorb the liquid with absorbent or soil, sweep up the saturated material, and place it in a labeled, lined container for disposal per the label. Triple-rinse the jug and add the rinseate to the spray tank if the label allows, then puncture and dispose of the jug through a container-recycling program or landfill as the label directs.
Report and document: if the spill threatens groundwater or surface water, or exceeds a reportable quantity, notify the Oregon Emergency Response System and DEQ per the label's spill statement and the SDS. Photograph the pad, note the volume and time, restock the spill kit, and fix the underlying problem: a loading pad draining toward a swale 30 feet from a well needs an air gap or backflow preventer at the fill hose and a containment curb, so a tipped jug can never reach that swale again.