Pesticides formulations: Granules (G)
A pesticide formulation is a combination of active and inert ingredients that forms an end-use pesticide product. Pesticides are formulated to make them safer or easier to use. This is because many pesticide active ingredients, in “pure” (technical grade) form, are not suitable for application. In their concentrated form, some are extremely toxic, many do not mix well with water, some are unstable, and some are difficult (or unsafe) to handle, transport, or store. To address these problems, manufacturers add inert ingredients to end-use pesticide products. Inert ingredients have no pesticidal activity, and some simply serve as diluents or carriers.
Granular formulations are similar to dust formulations; however, granular particles are larger and heavier. Like dusts, they are not water-soluble. They are ready-to-use–not intended to be mixed with water and applied as a liquid suspension. The coarse particles that serve as carriers for granular formulations are adsorptive substances like clay or absorptive plant material such as ground corncobs or walnut shells. The active ingredient either coats the outside of the granules or is absorbed into them. The amount of active ingredient is relatively low, usually ranging from 1% to 15%.
Because many granular formulations use carriers that absorb moisture, humidity will affect particle size and mass. This, in turn, will affect flow rate. Also, different “batches” of the same formulation may differ slightly in size or shape and density. For these reasons, you must calibrate granular application devices often.
Once applied, granules slowly release the adsorbed or absorbed active ingredient. Some require soil moisture, rain, or watering to initiate the release of the active ingredient. Other granules do so as they decompose.
Granular pesticides are mostly used to apply chemicals to the soil, where they control weeds, nematodes, and insects or are absorbed by plant roots. Most granular formulations are used to deliver systemic pesticides. Granules are a common choice in many sites and situations.
Aerial applicators sometimes use granular formulations to reduce drift or penetrate dense vegetation. Granular formulations are also useful in aquatic situations to control mosquito larvae and aquatic weeds.
- Ready-to-use; no mixing.
- Drift hazard is low, and particles settle quickly.
- Low applicator hazard: no spray; little dust.
- Weight carries the formulation through foliage to soil or water target.
- Applied with simple application equipment, such as seeders or fertilizer spreaders.
- May break down more slowly than Wettable powders (WPs) or Emulsifiable
concentrate (ECs) because of a slow-release coating.
- Application equipment needs frequent calibration.
- Application equipment is not as convenient to calibrate as spray equipment. Released particles are measured by weight instead of by volume.
- Uniform application may be difficult with some devices (e.g., rotary spreaders).
- Granules do not stick to foliage or other uneven surfaces. For this reason, contact products are rarely formulated this way.
- May need to be incorporated into soil or planting medium.
- May need moisture to release the active ingredient; may not be effective in drought conditions. May be hazardous to non-target species, especially waterfowl and other birds. This is because birds may feed on grain- or seed-like granules or mistake them for “grit” they need to grind up their food.
- Bulky; low percentage of active ingredient per unit volume.