Sandy Ground and a Shallow Water Table
A grower plans a preemergence herbicide application on 20 acres of sweet corn in sandy loam. The water table is about eight feet below the surface, and a lake is 300 feet from the field edge. The label carries a groundwater-advisory statement and requires incorporation within 24 hours unless rain occurs. The forecast is for 0.2 inch of rain, then dry weather. After the pass, about 50 gallons of mix remain. The grower wants to add a liquid fertilizer and a nonionic surfactant to the tank because a neighbor did. The label lists a maximum rate and does not mention fertilizer or surfactant. Available formulations are a 4L emulsifiable concentrate and a 75DF dry flowable. The well is 50 feet from the mixing pad.
1. How should the groundwater advisory and incorporation requirement shape the application decision?
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The advisory does not by itself prohibit the application, but it is a warning that the product can leach. On sandy loam with an eight-foot water table and a lake 300 feet away, the applicator should use the lowest labeled rate that will work, incorporate within 24 hours as the label requires, and avoid applying before a heavy rain. A 0.2-inch rain will not incorporate the product, so mechanical incorporation is needed. The applicator should also check the label for setbacks near wells, lakes, and drains and follow them. If the label has a prohibition rather than an advisory, the application cannot be made. The applicator should explain the difference to the grower and document the decision.
2. Evaluate the plan to add liquid fertilizer and a nonionic surfactant, and explain how formulation choice affects the decision.
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The fertilizer and surfactant cannot be added just because a neighbor did. Every tank-mix partner and adjuvant must be allowed by the label, and the applicator should jar-test the combination first. Liquid fertilizer can increase salt injury to corn and can change compatibility; a nonionic surfactant may increase uptake and injury or may be unnecessary. The applicator should also check the formulation: an EC may be more compatible with a fertilizer than a dry flowable, but it may also increase drift or crop injury. Mix in the correct order, keep agitation, and use a small test batch. If the label does not allow the additive, do not use it; choose a labeled alternative instead.
3. What should be done with the 50 gallons of leftover mix and the rinse water to protect the lake and well?
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The leftover mix and rinse water should not go down a drain, onto the mixing pad, or near the well or lake. The best option is to apply the leftover mix to the same labeled field at the labeled rate, as long as the total rate stays within the label. If that is not possible, use an approved disposal method from the label or state program. Triple-rinse containers and add the rinse water to the tank, then apply. Mix at least 50 feet from the well, use a spill kit, and contain rinse water. Record the amount and disposal method. The applicator should not store leftover mix indefinitely or dump it on a fence line.