8.6 Equipment Cleanout, Maintenance & Preventing Carryover Injury

8.6 Equipment Cleanout, Maintenance & Preventing Carryover Injury

A named competency: Colorado Part 4.39 lists "equipment including: calibration, selection of correct equipment for the job, maintenance and care, clean up, new equipment," and 40 CFR § 171.103(c)(6) requires competency in "the use, maintenance and calibration procedures" for application equipment. Calibration tells you whether the machine is delivering the right amount; cleanout and maintenance decide whether it will still do so tomorrow — and whether the next load injures a crop.

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1. Why Carryover Injury Happens

A sprayer is not a clean container. Active ingredient adheres to tank walls, hoses, the inside of the boom, filter housings, and the dead ends beyond the last nozzle. Some chemistries then release slowly into a subsequent load.

• Sulfonylurea and other ALS-inhibiting herbicides are applied at fractions of an ounce per acre, so a residue far too dilute to see can still injure a sensitive crop.
• Growth-regulator herbicides such as 2,4-D, dicamba, and clopyralid injure grapes, tomatoes, sunflowers, and many ornamentals at very low concentrations.
• Oil-based emulsifiable concentrates leave a film that traps residue and can later release it as a slug.

Injury usually shows up as cupping, twisting, or strapping of new growth several days after the second application — by which time the tank has been refilled again and the diagnosis is guesswork. This is why the label's cleaning procedure is a legal instruction, not a housekeeping tip.

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2. The Cleanout Sequence

┌─────────────────────────────────────────────────────────────────────────────┐
│                    SPRAYER CLEANOUT — STANDARD SEQUENCE                     │
├─────────────────────────────────────────────────────────────────────────────┤
│  0. PPE FIRST. Cleanout exposes you to concentrate, not dilute spray.       │
│  1. SPRAY OUT the remaining tank mix on a LABELED SITE at or below the      │
│     label rate. Do not let mix sit overnight in the tank.                   │
│  2. RINSE 1 — fill 10 percent of tank capacity with clean water, agitate,   │
│     circulate through the boom and out every nozzle, then spray out.        │
│  3. CLEANING AGENT — add the agent the LABEL specifies (household ammonia,  │
│     a commercial tank cleaner, or a detergent), fill, and CIRCULATE for the │
│     time the label states, often 15 minutes or more. Leave it in the boom.  │
│  4. RINSE 2 and RINSE 3 — clean water, circulate, spray out each time.      │
│  5. REMOVE AND CLEAN all screens, strainers, filters, nozzle tips and       │
│     nozzle bodies BY HAND. Open the BOOM END CAPS and flush the ends.       │
│  6. DRY and store with tips off; leave the tank open to air where safe.     │
└─────────────────────────────────────────────────────────────────────────────┘

Three rules govern the whole sequence:

1. Read the cleaning procedure on the label that was just applied, not on the one you are about to apply. The residue you are removing dictates the agent.
2. Volume beats time. Three small rinses remove far more residue than one large one, for exactly the same reason triple rinsing a container works better than a single fill.
3. Rinsate is a pesticide. Apply it to a site listed on the label at or below the labeled rate. It is not wash water, and it may not go to a storm drain, ditch, sanitary sewer, or bare ground near a wellhead.

[!WARNING] Boom end caps are the most commonly skipped step. Sediment and concentrated residue collect in the last few inches of each boom section where flow is slowest. A cleanout that never opens the end caps leaves the worst contamination in place.

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3. Filters, Screens, and Mesh

Screens protect the pump and the nozzle orifices, and they run coarse to fine in the direction of flow:

Two operating rules: a higher mesh number means finer openings, and nozzle screen mesh must never be finer than the nozzle manufacturer specifies for that orifice — an over-fine screen plugs constantly and starves the tip. Wettable powders and dry flowables demand coarser screens than solutions because the suspended solids are the product.

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4. Nozzle Wear and the 10 Percent Rule

Nozzle orifices erode. Abrasive suspensions (wettable powders, dry flowables), high pressure, and soft tip materials all accelerate it, and the failure is invisible — a worn tip sprays a wider, heavier stream that still looks correct.

The rule: replace any nozzle whose output exceeds 10 percent above the output of a new tip of the same size at the same pressure. Check tips by catching output from every nozzle for a fixed time and comparing.

Never clean a tip with a knife, wire, or nail. Use a soft brush, compressed air, or water — enlarging the orifice by even a little permanently changes the output and the pattern.

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5. Pumps, Seals, Hoses, and Tanks

Winterizing

Colorado sprayers freeze. Before storage: clean the system completely, drain all water, then circulate RV-type antifreeze through the pump, lines, and boom to protect seals and prevent freeze damage; remove and store nozzle tips and screens; grease fittings; store the tank open where possible and out of direct sunlight, which degrades polyethylene.

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6. Where the Wash Water Goes

Equipment washing is the classic point source contamination event: a single location, repeated daily, with concentrated residue.

• Wash on a designed mixing and loading pad with containment, or on a vegetated area well away from wells, ditches, and surface water, where the rinsate is applied at a rate no site receives repeatedly.
• Colorado's mixing and loading guidance keeps these operations well back from wells, streams, and irrigation ditches unless performed over engineered containment.
• Never wash equipment where the runoff can reach a storm drain, sanitary sewer, ditch, or well casing.
• Recycle rinsate into the next compatible load whenever the label allows it. That converts a waste stream into product and eliminates the disposal question entirely.