Calibration, Worn Nozzles, and a Tank Mix That Settles
An applicator is calibrating a 200-gallon boom sprayer before a postemergence herbicide application on 80 acres of soybeans. The sprayer has 11002 flat-fan nozzles spaced 20 inches apart on the boom and is operated at 40 psi and 4 mph. The applicator drives a 300-foot measured course and collects 26 fluid ounces from one nozzle. The nozzle catalog says a 11002 nozzle at 40 psi delivers 0.20 gallons per minute. The tank-mix label calls for a glyphosate product plus 2,4-D amine and a nonionic surfactant; the applicator also wants to add a clay-based flowable. In the tank, the clay settles to the bottom and forms a hard cake despite agitation. The applicator plans to increase pressure to 60 psi to 'push it through' and to add more surfactant.
1. Calculate the actual application rate in gallons per acre and determine whether the nozzles are within acceptable wear limits.
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First find the travel time for 300 feet at 4 mph: 4 mph is 352 feet per minute, so 300 divided by 352 equals about 0.852 minute. Convert the collected volume: 26 fluid ounces divided by 128 equals 0.203 gallon. The measured nozzle flow is 0.203 divided by 0.852, or about 0.238 gallon per minute. Use the boom formula: GPA equals gallons per minute times 5,940 divided by miles per hour times nozzle spacing. That is 0.238 times 5,940 divided by 4 times 20, or about 17.7 GPA. The catalog flow of 0.20 gpm would give 0.20 times 5,940 divided by 80, or about 14.9 GPA. The measured rate is about 19 percent higher than the new-nozzle rate, which exceeds the usual 10 percent wear limit. The applicator should replace the nozzles as a set and recalibrate before spraying.
2. What is wrong with the proposed tank-mix sequence and pressure increase, and how should the applicator correct it?
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Increasing pressure to 60 psi does not fix a settling clay; it increases drift, stresses the pump and plumbing, and may make the mixture less uniform. Adding more surfactant may cause foaming or make the incompatibility worse. The clay flowable should be handled as a dry-type formulation: make a slurry and add it to water under good agitation before the other products, following the label's mixing order. A jar test should be run with the actual products and water to see whether the combination is compatible. If the clay cakes or separates, the applicator should not spray the mixture; use a compatibility agent only if the label allows it, improve agitation, or apply the products separately. The tank and lines should be cleaned properly before switching products.
3. What records and calibration checks should be documented before spraying the 80 acres?
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The applicator should record the nozzle type and size, number and spacing, pressure, speed, measured flow, calculated GPA, and the calibration date. The record should also include the product names and EPA registration numbers, application rates, total tank mix, surfactant, water source, target weeds, crop and field location, applicator identity, and weather conditions. The jar-test result and any nozzle replacement should be noted. Before spraying, the applicator should verify that the tank is clean, agitation works, the boom height is correct, and the spray pattern is uniform. After the job, the actual acres treated and amount of product used should be reconciled with the planned rate. These records support label compliance and help diagnose streaking, overlap, or drift complaints.