9.1 Choosing an Application Method
Key Takeaways
- Application methods divide by where the product is placed - foliar, soil surface, soil incorporated, in-furrow, banded, directed, broadcast, spot, seed treatment, baiting, chemigation and fumigation.
- Placement drives both efficacy and exposure: soil incorporation reduces volatilization and photodegradation, in-furrow and seed treatment place product only where the crop needs it, and broadcast foliar work carries the greatest drift exposure.
- Aerial application covers acreage fast and avoids compaction and wet-field access problems, but it carries the highest drift risk and in Arkansas it triggers the numeric set-up rules in 2 CAR Sec. 72-102(a).
- Low-volume applications concentrate the spray solution and demand smaller droplets for coverage, which directly increases drift risk - the coverage-versus-drift trade-off is the central tension in method selection.
- The method must be one the label does not prohibit; FIFRA Section 2(ee) permits using a method not prohibited by the labelling, but never a site or a rate the label does not allow.
9.1 Choosing an Application Method
Core Concept: 40 C.F.R. Sec. 171.103(c)(7) makes application methods a competency area in its own right - selecting a method, preventing drift, and understanding fumigation and aerial application. The method is not a detail after product selection; it determines whether the product reaches the target, whether the crop is safe, how much the handler is exposed, and how much leaves the field.
Where the Product Goes
| Method | Placement | Best for | Main trade-off |
|---|---|---|---|
| Broadcast foliar | Uniformly over the whole surface | Post-emergence herbicides, foliar insecticides and fungicides | Highest drift exposure; treats the whole area whether it needs it or not |
| Band | A strip over or beside the row | Residual herbicides in row crops | Untreated middles need cultivation or a second pass |
| Directed / shielded | Aimed at the base of the crop or between rows, away from foliage | Products the crop would not tolerate overhead | Slower; requires accurate guidance and crop staging |
| Spot treatment | Individual plants or patches | Scattered escapes, perennial patches, hand-gun work | Operator-dependent output; calibrate per operator |
| Soil surface (preemergence) | On the soil, unincorporated | Residual herbicides activated by rain or irrigation | Needs moisture; volatile or photodegradable products lose activity |
| Soil incorporated (PPI) | Mixed mechanically into the soil | Volatile or photodegradable products | Requires tillage; incorporation depth and uniformity affect performance |
| In-furrow | In the seed furrow at planting | Insecticides, fungicides, nematicides, inoculants | Placement precision; potential seedling phytotoxicity |
| Seed treatment | On the seed itself | Early-season insect and disease protection | Handled at the seed level; a distinct Arkansas licence category |
| Baiting | Attractant plus toxicant in a station or granule | Rodents, ants, slugs, some insects | Bait placement and station security; non-target risk if not enclosed |
| Granular | Dry particles broadcast, banded or in-furrow | Soil-applied products; low drift | Requires moisture for activation; calibrate by catch-and-weigh |
| Chemigation | Through the irrigation system | Large acreages already under irrigation | Requires backflow prevention and interlocks - Section 9.3 |
| Fumigation | As a gas into soil or an enclosed space | Soilborne pests, stored commodities, structures | Highest acute hazard class - Section 9.4 |
| Aerial | Fixed-wing or rotary aircraft | Large acreage, wet fields, tall crops, time-critical work | Highest drift risk; triggers the Arkansas aerial set-up rules |
How Placement Changes Fate and Exposure
Section 5.5 established that fate depends on solubility, adsorption, persistence and volatility. Placement is the variable you control:
- Incorporating a volatile product converts a vapor drift problem into a soil-activity problem, which is why highly volatile soil herbicides carry PPI directions.
- Incorporating also protects photodegradable products from ultraviolet breakdown on the surface.
- In-furrow and seed treatment place a small quantity exactly where the crop needs it, which minimizes both total load and off-target movement - the reason these methods have grown at the expense of broadcast soil insecticides.
- Banding cuts total product per field acre in half or better while holding the in-band rate at the label rate.
- Directed and shielded application lets an applicator use a chemistry the crop cannot tolerate overhead, and simultaneously reduces drift because the spray is released low and aimed downward.
Aerial Application
Aerial work solves problems ground equipment cannot: hundreds of acres in a morning, saturated Delta fields with no ground access, tall or closed-canopy crops, and time-critical insect or disease events.
It also carries the highest drift risk of any method, which is why Arkansas writes numeric aerial rules directly into 2 CAR Sec. 72-102(a) - airspeed 145 mph, release height 15 feet above the crop canopy, nozzles rearward and at least 10 inches below the trailing edge, boom-to-wingspan 0.7 fixed-wing and 0.8 rotary, wind shear angle 30 degrees, minimum 2 gallons per acre, drift reduction nozzles, and a medium or larger droplet classification under ASABE S572. Section 1.6 covers these in full, and a private applicator using aircraft to apply herbicides must meet the same criteria.
Aerial applicators also work under buffer distances that are larger than ground buffers - Class F requires a 4-mile aerial buffer against susceptible crops where the general provisions apply, versus 1 mile for ground.
The Coverage-Versus-Drift Trade-Off
This is the tension underneath every method decision.
- Contact products need thorough coverage. Coverage improves with higher carrier volume and smaller droplets, because more, smaller droplets cover more surface per gallon.
- Smaller droplets drift. Droplets below about 150 microns are highly driftable, and driftable fines are conventionally counted below 105 microns.
- Systemic products tolerate coarser sprays, because the product redistributes inside the plant.
The resolution is not to pick one side but to change the variables that improve coverage without shrinking droplets:
- Raise carrier volume rather than reducing droplet size.
- Lower the boom and slow down - both reduce the time droplets spend airborne.
- Use air-induction nozzles, which produce large droplets containing air bubbles that collapse and spread on impact, giving coarse-spray drift behaviour with better-than-coarse coverage.
- Add a drift-reduction adjuvant where the label permits, understanding that it shifts the droplet spectrum rather than eliminating fines.
- Spray when conditions are right - the Arkansas inversion indicator, wind within limits, and wind direction away from sensitive receptors.
[!IMPORTANT] Exam Trap: Section 2(ee) and Application Method FIFRA Section 2(ee) permits employing any method of application not prohibited by the labelling. That is genuinely broad - if the label does not forbid aerial application, aerial application is not automatically off-label. What 2(ee) never permits is applying to a site not listed, above the labelled rate, or contrary to an express label prohibition. Read the Directions for Use for method language before assuming either way.
An applicator must treat 900 acres of soybeans for a rapidly developing insect infestation. Recent heavy rain has left the fields too wet for ground equipment, and the canopy has closed. Which consideration is most important in choosing aerial application?
A contact fungicide requires thorough coverage on a dense canopy, but the field borders a certified organic vegetable operation. Which adjustment improves coverage without increasing drift risk?
Why do highly volatile soil-applied herbicides carry preplant incorporated directions?