1.6 Arkansas Herbicide Application Equipment Set-Up Rules
Key Takeaways
- Arkansas writes numeric equipment set-up standards for herbicide applications to field crops directly into 2 CAR Sec. 72-102, and Class C, E and F products all incorporate those standards by reference.
- Aerial herbicide limits: airspeed 145 mph, release height 15 feet above the crop canopy, nozzles pointed rearward and at least 10 inches below the trailing edge, boom-to-wingspan ratio 0.7 fixed-wing and 0.8 rotary, wind shear angle 30 degrees, and a minimum 2 gallons per acre.
- Ground herbicide limits: 10 mph with medium droplets, 15 mph with coarse, above 15 mph only with very coarse; boom height 30 inches above canopy with medium droplets or 60 inches with coarse or larger; minimum 2 gallons per acre.
- Spray classification must be medium or larger under ASABE S572, and drift reduction nozzles meeting that classification are mandatory for both aerial and ground herbicide work.
- Inversion control is a recording duty: applications may not be made where spray could be entrained in an inversion, and the applicator must record the ambient temperature for each application - measured at the airstrip for aerial work and at the field for ground work.
1.6 Arkansas Herbicide Application Equipment Set-Up Rules
Core Concept: Most states leave spray equipment configuration to the label. Arkansas does not. 2 CAR Sec. 72-102(a) and (b) write numeric aerial and ground standards for herbicide spray applications to field crops directly into the rules, and Classes C, E, and F then pull those standards in by reference. Forestry is excluded. Where the product label is more restrictive than the rule, the label takes precedence.
These are among the most quotable, most testable numbers in Arkansas pesticide law, and they exist for a specific reason: the Delta's crop mosaic means an off-target auxin herbicide can destroy a neighbour's cotton or tomato crop from a mile away.
Aerial Herbicide Applications to Field Crops
Arkansas Aerial Herbicide Set-Up
┌──────────────────────────────────────────────────────────────┐
│ Airspeed <= 145 mph (documented exceptions allowed) │
│ Release height <= 15 ft above the crop canopy │
│ Nozzle aim rearward, >= 10 in below trailing edge │
│ Boom / wingspan <= 0.7 fixed-wing, <= 0.8 rotary-wing │
│ Wind shear <= 30 degrees nozzle discharge angle │
│ Carrier volume > 2 gal/acre unless the label says otherwise│
│ Droplet class medium or larger (ASABE S572, Aug. 1999) │
└──────────────────────────────────────────────────────────────┘
- Airspeed - 145 mph. When applying a herbicide, an aircraft may not exceed 145 mph. Higher airspeeds are permitted only if the operator can document that the chosen set-up and airspeed still meet the spray classification requirement. That documentation must be verified by a person or entity independent of the applicator or firm, with specific education, training, and experience in herbicide application to field crops, whose curriculum vitae is acceptable to the Board, and it must be recorded on a Board-provided form and supplied before the set-up is used.
- Release height - 15 feet. Spray boom height at the time of product release may not exceed 15 feet above the crop canopy. A higher elevation is allowed only in the vicinity of obstructions in or adjacent to the field that make 15 feet unsafe, and never where the label imposes a lower elevation.
- Nozzle placement. All spray nozzle discharges must be pointed toward the rear of the aircraft and a minimum of 10 inches below the trailing edge of the wing.
- Boom length ratio. Boom length divided by wingspan may not exceed 0.7 for fixed-wing and 0.8 for rotary-wing aircraft. This keeps the boom tips out of the wingtip vortices, which is where the finest, most drift-prone droplets get lofted.
- Wind shear angle - 30 degrees. The wind shear angle of the nozzle discharge may not exceed 30 degrees, and the spray classification requirement must still be met.
- Nozzles. Drift reduction nozzles - Reglo Jet, CP drift reduction tips, narrow-angle flat fans of 65 degrees or less, straight stream, or any configuration meeting the classification requirement - must be used, with documentation available to the Board on request.
- Carrier volume. Application rate must be greater than 2 gallons per acre unless the label requires otherwise.
- Spray classification. Must be in the medium or larger category under the August 1999 ASABE S572 report, Spray Nozzle Classification by Droplet Spectra.
Ground Herbicide Applications to Field Crops
| Droplet classification | Maximum vehicle speed | Maximum boom height above canopy |
|---|---|---|
| Medium | 10 mph or less | 30 inches |
| Coarse | 15 mph or less | 60 inches |
| Very coarse | may exceed 15 mph | 60 inches (coarse or larger) |
- Nozzle type. Applications are restricted to hydraulic-style nozzles that initiate droplet movement in the direction of the plant canopy. Rotary or controlled-droplet equipment that emits droplets horizontally may be used only if the spray classification meets medium or greater, verified by an independent qualified party in the same way as the aerial airspeed exception.
- Carrier volume. Minimum 2 gallons per acre unless the label requires otherwise.
- Drift reduction nozzles producing medium or greater classifications must be used.
- Label precedence. Where the label is more restrictive, the label controls.
The Inversion Test Is a Recording Duty
Both the aerial and the ground rule say the same thing, and it is worded as an affirmative record obligation rather than a prohibition you can eyeball:
Herbicide applications may not be made under conditions where the spray may possibly be entrained in an inversion layer. As an indicator that an inversion is unlikely to exist, the applicator shall record the ambient temperature for each application.
- Aerial: temperature measured at the airstrip from which the pilot is working.
- Ground: temperature measured at the field of application.
- The indicator: an inversion is much less likely if the temperature has increased 3 degrees Fahrenheit from the morning low at the time of application for applications made before noon, or has not decreased more than 3 degrees Fahrenheit from the afternoon high for applications made after noon.
- The applicator should also use other legal means available to verify an inversion does not exist.
[!IMPORTANT] Exam Trap: Two Different Afternoon Numbers The general herbicide set-up rule uses 3 degrees F in both directions. The Class F rule (2 CAR Sec. 70-111(i)) uses 3 degrees F above the morning low before noon but not more than a 5 degree F decrease from the afternoon high after noon, and it makes the temperature records mandatory for both the grower and the applicator. If the question involves 2,4-D or MCPA, use the Class F numbers.
How the Set-Up Rules Reach Other Classes
- Class C: all commercial equipment used to apply Class C products must comply with the herbicide set-up requirements before the initial application; the Department verifies the authorized set-up, must re-authorize any modification, and inspects the equipment annually at $25 per inspection.
- Class E / Class F: Class F products must be applied in accordance with the set-up rules, and those conditions extend beyond field crops to pastures, rights-of-way, drainage ditches, and brush and forest land.
- Private applicators using aircraft to apply herbicides must comply with the same aerial criteria as commercial applicators.
A fixed-wing operator with a 50-foot wingspan is configuring an aircraft for a herbicide application to soybeans. He plans a 40-foot boom, a release height of 12 feet above the canopy, an airspeed of 150 mph, and nozzles angled 20 degrees and mounted 12 inches below the trailing edge. Which element of this set-up violates 2 CAR Sec. 72-102(a) as described?
A ground applicator is spraying a herbicide on corn at 14 mph with a boom set 48 inches above the canopy, using nozzles producing a coarse droplet spectrum at 3 gallons per acre. Is this set-up compliant with the Arkansas ground herbicide rules?
An aerial applicator working a Class F 2,4-D application begins at 2:30 in the afternoon. The afternoon high measured at his airstrip was 88 degrees Fahrenheit; the temperature at the time of application is 82 degrees. What does the rule require?