Tank Mix Calculations and a Second Application
A 200-gallon ground sprayer will treat 45 acres of potatoes. Product A is an 80% water-dispersible granule at 1.5 lb of product per acre, with a maximum of two applications per season, a 14-day minimum interval, and a 30-day preharvest interval. Product B is an emulsifiable concentrate at 12 fl oz/acre. The label recommends a nonionic surfactant at 0.25% v/v, or a crop oil concentrate at 1% v/v when the tank mix includes an EC. Target carrier volume is 15 GPA. Product A was applied 15 days ago. The water source tests 420 ppm hardness at pH 8.4, and the previous tank held a sulfonylurea herbicide.
1. Calculate acres per tank and the amount of each product per full tank.
Read the worked answer
Acres per tank 200 gal ÷ 15 gal/acre = 13.33 acres per full tank
Product A (80 WDG) 1.5 lb/acre × 13.33 acres = 20 lb of product
Product B (EC) 12 fl oz/acre × 13.33 acres = 160 fl oz = 1.25 gal
Adjuvant The EC is present, so use the crop oil concentrate at 1% v/v: 1% × 200 gal = 2 gal COC
Practical note: mix only enough for the acres actually sprayed. For 45 acres you need about 3.4 tanks (45 ÷ 13.33). Measure each partial load separately rather than scaling the last tank from a full-load figure.
2. Recommend the mixing/loading sequence and the compatibility steps you would take, given the water quality and the previous tank contents.
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Before loading
- Clean the tank thoroughly because a sulfonylurea residue can injure potatoes at very low concentrations. Use the labeled tank-cleaning procedure, including a rinse of the boom, screens, and sump.
- Run a jar test with the actual water source and the exact product ratios.
Mixing order
- Fill the tank about half full with water.
- Check pH. At pH 8.4, confirm that both labels permit that pH or require a buffer; add buffer first if the label allows.
- Add the WDG as a pre-slurry while agitating. Dry products go in before liquids.
- Add the EC.
- Add the COC last.
- Bring to final volume and maintain agitation.
Water hardness 420 ppm hardness can reduce performance of some products. If the label specifies a water conditioner or ammonium sulfate, add it before the products. Do not assume a conditioner is compatible with every product.
Jar test Watch for flocculation, oil separation, or heat. If incompatibility appears, do not load the tank.
3. Is the second application legal now? What constraints govern it?
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- Interval: 15 days have passed, so the 14-day minimum interval is met.
- Seasonal maximum: this would be application two of two, so no further Product A applications are allowed after it.
- Preharvest interval: harvest must be at least 30 days after the second application. Check the calendar against the intended harvest date before spraying.
- Crop stage and rate: the label may restrict application by growth stage and by total product per season; confirm both.
- Resistance management: two applications of the same site of action in one season increase selection pressure. Consider whether the second application is truly needed and whether it fits the resistance-management plan.
- Tank mix: confirm Product B's interval and PHI as well, since the two products may have different restrictions.
If any one of these conditions fails, the application must be postponed or redesigned.